2016.10.31

UG-SLDVRTL

Altera Virtual JTAG (altera_virtual_jtag) IP Core User
Guide
Subscribe

Send Feedback

The Altera Virtual JTAG (altera_virtual_jtag) megafunction IP core provides access to the PLD source
through the JTAG interface. This IP core is optimized for Altera device architectures. Using IP cores inplace of coding your own logic saves valuable design time, and offers more efficient logic synthesis anddevice implementation. You can scale the IP core's size by setting parameters.
Related Information

Introduction to Altera IP Cores

Introduction
The Virtual JTAG IP core allows you to create your own software solution for monitoring, updating, anddebugging designs through the JTAG port without using I/O pins on the device, and is one feature in the
On-Chip Debugging Tool Suite. The Quartus® II software or JTAG control host identifies each instance of
this IP core by a unique index. Each IP core instance functions in a flow that resembles the JTAG
operation of a device. The logic that uses this interface must maintain the continuity of the JTAG chain on
behalf the PLD device when this instance becomes active.
With the Virtual JTAG IP core you can build your design for efficient, fast, and productive debugging
solutions. Debugging solutions can be part of an evaluation test where you use other logic analyzers to
debug your design, or as part of a production test where you do not have a host running an embedded
logic analyzer. In addition to debugging features, you can use the Virtual JTAG IP core to provide a single
channel or multiple serial channels through the JTAG port of the device. You can use serial channels inapplications to capture data or to force data to various parts of your logic.
Each feature in the On-Chip Debugging Tool Suite leverages on-chip resources to achieve real time
visibility to the logic under test. During runtime, each tool shares the JTAG connection to transmit
collected test data to the Quartus II software for analysis. The tool set consists of a set of GUIs, IP core
intellectual property (IP) cores, and Tcl application programming interfaces (APIs). The GUIs provide theconfiguration of test signals and the visualization of data captured during debugging. The Tcl scriptinginterface provides automation during runtime.
The Virtual JTAG IP core provides you direct access to the JTAG control signals routed to the FPGA core
logic, which gives you a fine granularity of control over the JTAG resource and opens up the JTAG
resource as a general-purpose serial communication interface. A complete Tcl API is available for sending
and receiving transactions into your device during runtime. Because the JTAG pins are readily accessible© 2016 Intel Corporation. All rights reserved. Intel, the Intel logo, Altera, Arria, Cyclone, Enpirion, MAX, Megacore, NIOS, Quartus and Stratix words and logos
are trademarks of Intel Corporation in the US and/or other countries. Other marks and brands may be claimed as the property of others. Intel warrants
performance of its FPGA and semiconductor products to current specifications in accordance with Intel's standard warranty, but reserves the right to makechanges to any products and services at any time without notice. Intel assumes no responsibility or liability arising out of the application or use of any
information, product, or service described herein except as expressly agreed to in writing by Intel. Intel customers are advised to obtain the latest version ofdevice specifications before relying on any published information and before placing orders for products or services.

www.altera.com
101 Innovation Drive, San Jose, CA 95134

ISO
9001:2008
Registered

2

UG-SLDVRTL
2016.10.31

Installing and Licensing IP Cores

during runtime, this IP core enables an easy way to customize a JTAG scan chain internal to the device,
which you can then use to create debugging applications.
Examples of debugging applications include induced trigger conditions evaluated by a SignalTap® II Logic
Analyzer by exercising test signals connected to the analyzer instance, a replacement for a front panel
interface during the prototyping phase of the design, or inserted test vectors for exercising the design
under test.
The infrastructure is an extension of the JTAG protocol for use with Altera-specific applications and user
applications, such as the SignalTap II Logic Analyzer.

Installing and Licensing IP Cores
The software installation includes the FPGA IP library. This library provides useful IP core functions foryour production use without the need for an additional license. Some IP functions in the library requirethat you purchase a separate license for production use. The OpenCore® feature allows evaluation of any
FPGA IP core in simulation and compilation in the software. Upon satisfaction with functionality andperformance, visit the Self Service Licensing Center to obtain a license number for any FPGA product.
The software installs IP cores in the following locations by default:
Figure 1: IP Core Installation PathintelFPGA(_pro*)
quartus - Contains the Quartus Prime software
ip - Contains the IP library and third-party IP coresaltera - Contains the IP library source code
<IP core name> - Contains the IP core source files

Table 1: IP Core Installation Locations
Location

SoftwarePlatform<drive>:\intelFPGA_pro\quartus\ip\
alteraWindows<drive>:\intelFPGA\quartus\ip\altera

Windows<home directory>:/intelFPGA_pro/
quartus/ip/altera

Linux<home directory>:/intelFPGA/quartus/
ip/altera

Linux

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

On-Chip Debugging Tool Suite

3

On-Chip Debugging Tool Suite
The On-Chip Debugging Tool Suite enables real time verification of a design and includes the following
tools:
Table 2: On-Chip Debugging Tool Suite
Tool

Description

Typical Circumstances for Use

SignalTap II Logic Analyzer

Uses FPGA resources to sample tests You have spare on-chip memory
nodes and outputs the information and want functional verification
to the Quartus II software forof your design running in
display and analysis.
hardware.

SignalProbe

Incrementally routes internal signals
to I/O pins while preserving theresults from your last place-androute.

You have spare I/O pins andwant to check the operation of asmall set of control pins using
either an external logic analyzer
or an oscilloscope.

Logic Analyzer Interface (LAI)

Multiplexes a larger set of signals toa smaller number of spare I/O pins.
LAI allows you to select which
signals are switched onto the I/O
pins over a JTAG connection.

You have limited on-chip
memory and have a large set ofinternal data buses that you wantto verify using an external logic
analyzer. Logic analyzer vendors,such as Tektronics and Agilent,
provide integration with the tool
to improve usability.

In-System Memory Content
Editor

Displays and allows you to edit
on-chip memory.

You want to view and edit thecontents of either the instruction
cache or data cache of a Nios® IIprocessor application.

In-System Sources and Probes

Provides a way to drive and sample
logic values to and from internal
nodes using the JTAG interface.

You want to prototype a front
panel with virtual buttons foryour FPGA design.

Virtual JTAG Interface

Opens the JTAG interface so thatyou can develop your own custom
applications.

You want to generate a large setof test vectors and send them toyour device over the JTAG port
to functionally verify your design
running in hardware.

Related Information

System Debugging Tools Overview

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

4

UG-SLDVRTL
2016.10.31

Applications of the Virtual JTAG IP Core

Applications of the Virtual JTAG IP Core
You can instantiate single or multiple instances of the Virtual JTAG IP core in your HDL code. During
synthesis, the Quartus II software assigns unique IDs to each instance, so that each instance is accessedindividually. You can instantiate up to 128 instances of the Virtual JTAG IP core. The figure below shows atypical application in a design with multiple instances of the IP core.
Figure 2: Application Example

Logic

sld_virtual_jtag
Logic
tck
tms
trst

J TAG

sld_virtual_jtag

tdi
tdo

The hub automatically arbitrates between multiple applications that share a single JTAG resource.
Therefore, you can use the IP core in tandem with other on-chip debugging applications, such as the
SignalTap II Logic Analyzer, to increase debugging visibility. You can also use the IP core to provide simple
stimulus patterns to solicit a response from the design under test during run-time, including the following
applications:• To diagnose, sample, and update the values of internal parts of your logic. With this IP core, you caneasily sample and update the values of the internal counters and state machines in your hardware
device.
• To build your own custom software debugging IP using the Tcl commands to debug your hardware.
This IP communicates with the instances of the Virtual JTAG IP core inside your design.
• To construct your design to achieve virtual inputs and outputs.
• If you are building a debugging solution for a system in which a microprocessor controls the JTAG
chain, you cannot use the SignalTap II Logic Analyzer because the JTAG control must be with themicroprocessor. You can use low-level controls for the JTAG port from the Tcl commands to direct
microprocessors to communicate with the Virtual JTAG IP core inside the device core.

JTAG Protocol
The original intent of the JTAG protocol (standardized as IEEE 1149.1) was to simplify PCBinterconnectivity testing during the manufacturing stage. As access to integrated circuit (IC) pins became
more limited due to tighter lead spacing and FPGA packages, testing through traditional probing
Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

JTAG Circuitry Architecture

5

techniques, such as “bed-of-nails” test fixtures, became infeasible. The JTAG protocol alleviates the needfor physical access to IC pins via a shift register chain placed near the I/O ring. This set of registers near
the I/O ring, also known as boundary scan cells (BSCs), samples and forces values out onto the I/O pins.
The BSCs from JTAG-compliant ICs are daisy-chained into a serial-shift chain and driven via a serialinterface.
During boundary scan testing, software shifts out test data over the serial interface to the BSCs of selectICs. This test data forces a known pattern to the pins connected to the affected BSCs. If the adjacent IC at
the other end of the PCB trace is JTAG-compliant, the BSC of the adjacent IC samples the test pattern andfeeds the BSCs back to the software for analysis. The figure below illustrates the boundary-scan testing
concept.
Figure 3: IEEE Std. 1149.1 Boundary-Scan Testing
SerialData In

Boundary-Scan Cell
IC Pin Signal

SerialData Out

Core
Logic

Core
Logic

J TAG Device 1

Interconnection
to be Tested

J TAG Device 2

Because the JTAG interface shifts in any information to the device, leaves a low footprint, and is available
on all Altera devices, it is considered a general purpose communication interface. In addition to boundary
scan applications, Altera devices use the JTAG port for other applications, such as device configurationand on-chip debugging features available in the Quartus II software.
Related Information

IEEE 1149.1 JTAG Boundary-Scan Testing

JTAG Circuitry Architecture
The basic architecture of the JTAG circuitry consists of the following components:••••

A set of Data Registers (DRs)
An Instruction Register (IR)A state machine to arbitrate data (known as the Test Access Port (TAP) controller)
A four- or five-pin serial interface, consisting of the following pins:
•
•
•
•
•

Test data in (TDI), used to shift data into the IR and DR shift register chains
Test data out (TDO), used to shift data out of the IR and DR shift register chains
Test mode select (TMS), used as an input into the TAP controller
TCK, used as the clock source for the JTAG circuitry
TRST resets the TAP controller. This is an optional input pin defined by the 1149.1 standard.

Note: The TRST pin is not present in the Cyclone device family.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

6

JTAG Circuitry Architecture

UG-SLDVRTL
2016.10.31

The bank of DRs is the primary data path of the JTAG circuitry. It carries the payload data for all JTAG
transactions. Each DR chain is dedicated to serving a specific function. Boundary scan cells form theprimary DR chain. The other DR chains are used for identification, bypassing the IC during boundary
scan tests, or a custom set of register chains with functions defined by the IC vendor. Altera uses two of the
DR chains with user-defined IP that requires the JTAG chain as a communication resource, such as the
on-chip debugging applications. The Virtual JTAG IP core, in particular, allows you to extend the two DR
chains to a user-defined custom application.
You use the instruction register to select the bank of Data Registers to which the TDI and TDO must
connect. It functions as an address register for the bank of Data Registers. Each IR instruction maps to a
specific DR chain.
All shift registers that are a part of the JTAG circuitry (IR and DR register chains) are composed of two
kinds of registers: shift registers, which capture new serial shift input from the TDI pin, and parallel holdregisters, which connect to each shift register to hold the current input in place when shifting. The parallel
hold registers ensure stability in the output when new data is shifted.
The figure below shows a functional model of the JTAG circuitry. The TRST pin is an optional pin in the1149.1 standard and not available in Cyclone devices. The TAP controller is a hard controller; it is notcreated using programmable resources. The major function of the TAP controller is to route test data
between the IR and DR register chains.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

System-Level Debugging Infrastructure

7

Figure 4: Functional Model of the JTAG Circuitry
TDI
Tap
Controller
Output (3)IR Shift Registers

TDO

IR Update Registers

Tap
Controller
Output (3)DR Shift Register 1
DR Update Register 1
DR Shift Register 2
DR Update Register 2

DR Shift Register n
DR Update Register n

TMS
TCK
TRS T (1)J TAG TA P
Controller(2)

System-Level Debugging Infrastructure
On-chip debugging tools that require the JTAG resources share two Data Register chain paths; USER1 and
USER0 instructions select the Data Register chain paths. The datapaths are an extension of the JTAG
circuitry for use with the programmable logic elements in Altera devices.
Because the JTAG resource is shared among multiple on-chip applications, an arbitration scheme must
define how the USER0 and USER1 scan chains are allocated between the different applications. The systemlevel debugging (SLD) infrastructure defines the signaling convention and the arbitration logic for all
programmable logic applications using a JTAG resource. The figure below shows the SLD infrastructurearchitecture.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

8

UG-SLDVRTL
2016.10.31

Transaction Model of the SLD Infrastructure

Figure 5: System Level Debugging Infrastructure Functional Model
FPG A

Use r’s Design(Core Logic)

SLD Node
SLD Node
SLD Hub
SLD NodeTC
TMTD

SLD Node
J TAG Tap
Controller

TD

Transaction Model of the SLD Infrastructure
In the presence of an application that requires the JTAG resource, the Quartus II software automatically
implements the SLD infrastructure to handle the arbitration of the JTAG resource. The communicationinterface between JTAG and any IP cores is transparent to the designer. All components of the SLD
infrastructure, except for the JTAG TAP controller, are built using programmable logic resources.
The SLD infrastructure mimics the IR/DR paradigm defined by the JTAG protocol. Each application
implements an Instruction Register, and a set of Data Registers that operate similarly to the Instruction
Register and Data Registers in the JTAG standard. Note that the Instruction Register and the Data Registerbanks implemented by each application are a subset of the USER1 and USER0 Data Register chains. The
SLD infrastructure consists of three subsystems: the JTAG TAP controller, the SLD hub, and the SLD
nodes.
The SLD hub acts as the arbiter that routes the TDI pin connection between each SLD node, and is a statemachine that mirrors the JTAG TAP controller state machine.
The SLD nodes represent the communication channels for the end applications. Each instance of IP
requiring a JTAG communication resource, such as the SignalTap II Logic Analyzer, would have its own
communication channel in the form of a SLD node interface to the SLD hub. Each SLD node instance has
its own Instruction Register and bank of DR chains. Up to 255 SLD nodes can be instantiated, depending
on resources available in your device.
Together, the sld_hub and the SLD nodes form a virtual JTAG scan chain within the JTAG protocol. It isvirtual in the sense that both the Instruction Register and DR transactions for each SLD node instance areencapsulated within a standard DR scan shift of the JTAG protocol.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

SLD Hub Finite State Machine

9

The Instruction Register and Data Registers for the SLD nodes are a subset of the USER1 and USER0 Data
Registers. Because the SLD Node IR/DR register set is not directly part of the IR/DR register set of the
JTAG protocol, the SLD node Instruction Register and Data Register chains are known as Virtual IR (VIR)
and Virtual DR (VDR) chains. The figure below shows the transaction model of the SLD infrastructure.
Figure 6: Extension of the JTAG Protocol for PLD Applications
TDI
TA P
Controller
OutputIR Shift Registers

TDO

IR Update Registers

TA P
Controller
OutputDR Shift Register 1
DR Update Register 1

Altera PLD J TAG Extension
USER 0 Data Registers

USER 1 Data Registers

USER0 / USER1 and
SLD_HUB Control Signals

Altera PLD J TAG Extension

Node 1
VIR
VDR 1
VDR N
TDI

TDO
Node N
VIR
VIR 1
VIR N

SLD Hub Finite State Machine
The SLD hub decodes TMS independently from the hard JTAG TAP controller state machine andimplements an equivalent state machine (called the “SLD hub finite state machine”) for the internal JTAG
path. The SLD hub performs a similar function for the VIR and VDR chains that the TAP controller
Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

10

UG-SLDVRTL
2016.10.31

Virtual JTAG Interface Description

performs for the JTAG IR and DR chains. It enables an SLD node as the active path for the TDI pin, selects
the TDI data between the VIR and VDR registers, controls the start and stop of any shift transactions, andcontrols the data flow between the parallel hold registers and the parallel shift registers of the VIR and
VDR.
Because all shifts to VIR and VDR are encapsulated within a DR shift transaction, an additional control
signal is necessary to select between the VIR and VDR data paths. The SLD hub uses the USER1 command
to select the VIR data path and the USER0 command to select the VDR data path.
This state information, including a bank of enable signals, is forwarded to each of the SLD nodes. The SLD
nodes perform the updates to the VIR and VDR according to the control states provided by the sld_hub.
The SLD nodes are responsible for maintaining continuity between the TDI and TDO pins.
The figure below shows the SLD hub finite state machine. There is no direct state signal available to use forapplication design.
Figure 7: sld_hub Finite State Machine
JTAG_Test_Logic_Reset
JTAG_Run_Test_Idle

USR0

USR1

Virtual_Select_DR_Scan (1)Virtual_Select_IR_Scan (1)Virtual_Capture_DR

Virtual_Capture_IR

Virtual_Shift_DR

Virtual_Shift_IR (1)Virtual_Exit1_DR

Virtual_Exit1_IR (1)Virtual_Pause_DR

Virtual_Pause_IR (1)Virtual_Exit2_DR

Virtual_Exit2_IR (1)Virtual_Update_DR

Virtual_Update_IR

Virtual JTAG Interface Description
The Virtual JTAG Interface implements an SLD node interface, which provides a communication interface
to the JTAG port. The IP core exposes control signals that are part of the SLD hub; namely, JTAG port
signals, all finite state machine controller states of the TAP controller, and the SLD hub finite statemachine. Additionally, each instance of the Virtual JTAG IP cores contain the virtual Instruction Registerfor the SLD node. Instantiation of this IP core automatically infers the SLD infrastructure, and one SLD
node is added for each instantiation.
Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Virtual JTAG Interface Description

11

The Virtual JTAG IP core provides a port interface that mirrors the actual JTAG ports. The interface
contains the JTAG port pins, a one-hot decoded output of all JTAG states, and a one-hot decoded output
of all the virtual JTAG states. Virtual JTAG states are the states decoded from the SLD hub finite statemachine. The ir_in and ir_out ports are the parallel input and output to and from the VIR. The VIR
ports are used to select the active VDR datapath. The JTAG states and TMS output ports are provided fordebugging purposes only. Only the virtual JTAG, TDI, TDO, and the IR signals are functional elements of
the IP core. When configuring this IP core using the parameter editor, you can hide TMS and the decoded
JTAG states.
The figure below shows the input and output ports of the virtual JTAG IP core. The JTAG TAP controller
outputs and TMS signals are used for informational purposes only. These signals can be exposed using theCreate primitive JTAG state signal ports option in the parameter editor.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

12

UG-SLDVRTL
2016.10.31

Input Ports

Figure 8: Input and Output Ports of the Virtual JTAG IP Core

Inputs

One-Hot Decoded Outputs
from the SLD Hub FSM

One-Hot Decoded Outputs
from theTAP Controller

Input Ports
Table 3: Input Ports for the Virtual JTAG IP CorePort nametdo

Altera Corporation

RequiredYes

Description

Comments

Writes to the TDO pin on thedevice.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Output Ports

Port nameir_out[]RequiredNo

Description

Virtual JTAG instruction register
output. The value is captured
whenever virtual_state_cir is
high.

13

Comments

Input port [SLD_IR_WIDTH1..0] wide. Specify the widthof this bus with the SLD_IR_
WIDTH parameter.

Output Ports
Table 4: Output Ports for the Virtual JTAG IP CorePort Name

Required

Description

Comments

tck

Yes

JTAG test clock.

Connected directly to the TCK
device pin. Shared among all
virtual JTAG instances.

tdi

Yes

TDI input data on the device.
Shared among all virtual
Used when virtual_state_sdr JTAG instances.
is high.

ir_in[]

No

Virtual JTAG instruction registerdata. The value is available andlatched when virtual_state_
uir is high.

Output port [SLD_IR_
WIDTH-1..0] wide. Specify
the width of this bus with the
SLD_IR_WIDTH parameter.

Table 5: High-Level Virtual JTAG State Signals
Port Name

Required

Description

Comments

virtual_state_cdr

No

Indicates that virtual JTAG isin Capture_DR state.

virtual_state_sdr

Yes

Indicates that virtual JTAG isin Shift_​DR state.

virtual_state_e1dr

No

Indicates that virtual JTAG isin Exit1_DR state.

virtual_state pdr

No

Indicates that virtual JTAG isin Pause_DR state.

The Quartus II software
does not cycle through thisstate using the Tcl
command.

virtual_state_e2dr

No

Indicates that virtual JTAG isin Exit2_DR state.

The Quartus II software
does not cycle through thisstate using the Tcl
command.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

In this state, this instance isrequired to establish the
JTAG chain for this device.

Altera Corporation

14

UG-SLDVRTL
2016.10.31

Output Ports

Port Name

Required

Description

virtual_state_udr

No

Indicates that virtual JTAG is
in Update_DR state.

virtual_state_cir

NoIndicates that virtual JTAG isin Capture_IR state.

virtual_state_uir

NoIndicates that virtual JTAG is
in Update_IR state.

Comments

Table 6: Low-Level Virtual JTAG State Signals
Port Name

Required

Description

Comments

jtag_state_tlr

No

Indicates that the device JTAG Shared among all virtual
controller is in the Test_Logic_ JTAG instances.
Reset state.

jtag_state_rti

NoIndicates that the device JTAG Shared among all virtual
controller is in the Run_Test/ JTAG instances.
Idle state.

jtag_state_sdrs

No

Indicates that the device JTAG Shared among all virtual
controller is in the Select_DR_ JTAG instances.
Scan state.

jtag_state_cdr

No

Indicates that the device JTAG Shared among all virtual
controller is in the Capture_
JTAG instances.
DR state.

jtag_state_sdr

No

Indicates that the device JTAG Shared among all virtual
controller is in the Shift_​DR
JTAG instances.
state.

jtag_state_e1dr

No

Indicates that the device JTAG Shared among all virtual
controller is in the Exit1_DR
JTAG instances.
state.

jtag_state_pdr

No

Indicates that the device JTAG Shared among all virtual
controller is in the Pause_DR JTAG instances.
state.

jtag_state_e2dr

No

Indicates that the device JTAG Shared among all virtual
controller is in the Exit2_DR
JTAG instances.
state.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Output Ports

Port Name

Required

Description

Comments

jtag_state_udr

No

Indicates that the device JTAG Shared among all virtual
controller is in the Update_DR JTAG instances.
state.

jtag_state_sirs

No

Indicates that the device JTAG Shared among all virtual
controller is in the Select_IR_ JTAG instances.
Scan state.

jtag_state_cir

NoIndicates that the device JTAG Shared among all virtual
controller is in the Capture_IR JTAG instances.
state.

jtag_state_sir

NoIndicates that the device JTAG Shared among all virtual
controller is in the Shift_​IR
JTAG instances.
state.

jtag_state_e1ir

No

Indicates that the device JTAG Shared among all virtual
controller is in the Exit1_IR
JTAG instances.
state.

jtag_state_pir

NoIndicates that the device JTAG Shared among all virtual
controller is in the Pause_IR
JTAG instances.
state.

jtag_state_e2ir

No

Indicates that the device JTAG Shared among all virtual
controller is in the Exit2_IR
JTAG instances.
state.

jtag_state_uir

Indicates that the device JTAG Shared among all virtual
controller is in the Update_IR JTAG instances.
state.

tms

TMS input pin on the device.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

15

Shared among all virtual
JTAG instances.

Altera Corporation

16

UG-SLDVRTL
2016.10.31

Parameters

Parameters
Table 7: Virtual JTAG Parameters
Parameter

Type

Required

Description

SLD_AUTO_INSTANCE_INDEX

StringYesSpecifies whether the Compiler automaticallyassigns an index to the Virtual JTAG
instance. Values are YES or NO. When you
specify NO, you can find the auto assigned
value of INSTANCE_ID in the quartus_map
file. When you specify NO, you must define
INSTANCE_INDEX. If the index specified is notunique in a design, the Compiler automati‐
cally reassigns an index to the instance. The
default value is YES.

SLD_INSTANCE_INDEX

IntegerNo

Specifies a unique identifier for every instanceof alt_virtual_jtag when AUTO_INSTANCE_ID is specified to YES. Otherwise, this value isignored.

SLD_IR_WIDTH

IntegerYesSpecifies the width of the instruction register

ir_in[] of this virtual JTAG between 1 and24. If omitted, the default is 1.

Design Flow of the Virtual JTAG IP Core
Designing with the Virtual JTAG IP core includes the following processes:• Configuring the Virtual JTAG IP core with the desired Instruction Register length and instantiating the
IP core.
• Building the glue logic for interfacing with your application.
• Communicating with the Virtual JTAG instance during runtime.
In addition to the JTAG datapath and control signals, the Virtual JTAG IP core encompasses the VIR. The
Instruction Register size is configured in the parameter editor. The Instruction Register port on the Virtual
JTAG IP core is the parallel output of the VIR. Any updated VIR information can be read from this port
after the virtual_state_uir signal is asserted.
After instantiating the IP core, you must create the VDR chains that interface with your application. To dothis, you use the virtual instruction output to determine which VDR chain is the active datapath, and thencreate the following:• Decode logic for the VIR• VDR chains to which each VIR maps
• Interface logic between your VDR chains and your application logic

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Design Flow of the Virtual JTAG IP Core

17

Your glue logic uses the decoded one-hot outputs from the IP core to determine when to shift and when to
update the VDR. Your application logic interfaces with the VDR chains during any one of the non-shift
virtual JTAG states.
For example, your application logic can parallel read an updated value that was shifted in from the JTAG
port after the virtual_state_uir signal is asserted. If you load a value to be shifted out of the JTAG port,
you would do so when the virtual_state_cdr signal is asserted. Finally, if you enable the shift register toclock out information to TDO, you would do so during the assertion of virtual_state_sdr.
Maintaining TDI-to-TDO connectivity is important. Ensure that all possible instruction codes map to an
active register chain to maintain connectivity in the TDI-to-TDO datapath. Altera recommends including a
bypass register as the active register for all unmapped IR values.
Note that TCK (a maximum 10-MHz clock, if using an Altera programming cable) provides the clock forthe entire SLD infrastructure. Be sure to follow best practices for proper clock domain crossing between
the JTAG clock domain and the rest of your application logic to avoid metastability issues. The decoded
virtual JTAG state signals can help determine a stable output in the VIR and VDR chains.
After compiling and downloading your design into the device, you can perform shift operations directly to
the VIR and VDR chains using the Tcl commands from the quartus_stp executable and an Altera
programming cable (for example, a USB-Blaster™, a MasterBlaster™, or a ByteBlaster™ II cable). The
quartus_stp executable is a command-line executable that contains Tcl commands for all on-chip debug
features available in the Quartus II software.
The figure below shows the components of a design containing one instance of the Virtual JTAG IP core.
The TDI-to-TDO datapath for the virtual JTAG chain, shown in red, consists of a bank of DR registers.
Input to the application logic is the parallel output of the VDR chains. Decoded state signals are used tosignal start and stop of shift transactions and signals when the VDR output is ready.
The IR_out port, not shown, is an optional input port you can use to parallel load the VIR from the FPGA
core logic.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

18

UG-SLDVRTL
2016.10.31

Simulation Model

Figure 9: Block Diagram of a Design with a Single Virtual JTAG Instantiation
Inferred by Instantiationof Megafunction

Glue Logic between VJI and User Design(Created by Designer)
VJI Megafunction
Instance

TDI
TDO

SLD
Hub

TMS
TCK

IR

Original Design

TMS & Decoded
State Signals
IR_in

InputVector 1
TDI

InputVector 2

TDO

VDR Chain n

Application
Logic
VDR Chain 2

JTAGTAP
Controller

VDR Chain 1

TRS T

InputVector n

Simulation Model
The virtual JTAG IP core contains a functional simulation model that provides stimuli that mimic VIR and
VDR shifts. You can configure the stimuli using the parameter editor. You can use this simulation model
for functional verification only, and the operation of the SLD hub and the SLD node-to-hub interface is
not provided in this simulation model.

Run-Time Communication
The Tcl API for the Virtual JTAG IP core consists of a set of commands for accessing the VIR and VDR ofeach virtual JTAG instance.
These commands contain the underlying drivers for accessing an Altera programming cable and for
issuing shift transactions to each VIR and VDR. The table below provides the Tcl commands in thequartus_stp executable that you can use with the Virtual JTAG IP core, and are intended for designs thatuse a custom controller to drive the JTAG chain.
Each instantiation of the Virtual JTAG IP core includes an instance index. All instances are sequentiallynumbered and are automatically provided by the Quartus II software. The instance index starts at instanceindex 0. The VIR and VDR shift commands described in the table decode the instance index and provide
an address to the SLD hub for each IP core instance. You can override the default index provided by the
Quartus II software during configuration of the IP core.
The table below provides the Tcl commands in the quartus_stp executable that you can use with the
Virtual JTAG IP core, and are intended for designs that use a custom controller to drive the JTAG chain.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Run-Time Communication

19

Table 8: Virtual JTAG IP Core Tcl Commands
CommandDevice virtual ir shift

Arguments-instance_index <instance_index>-ir_value <numeric_ir_value>-no_captured_ir_value(1)-show_equivalent_device_ir_dr_
shift(1)

Device virtual dr shift-instance_index <instance_index>-dr_value <dr_value>

Description

Perform an IR shift operation to
the virtual JTAG instance specified
by the instance_index. Note that
ir_value takes a numericalargument.

Perform a DR shift operation to
the virtual JTAG instance.

-length <data_register_length>-no_captured_dr_value(1)-show_equivalent_device_ir_dr_shift-value_in_hex(1)Get hardware names

NONE

Queries for all available program‐ming cables.

Open device-device_name <device_name>

Selects the active device on the
JTAG chain.

-hardware_name <hardware_name>

Close device

NONE

Ends communication with theactive JTAG device.

Device lock

-timeout <timeout>

Obtains exclusive communication
to the JTAG chain.

Device unlock

NONE

Releases device_lock.

Device ir shift-ir_value <ir_value>

Performs a IR shift operation.

-no_captured_ir_value

Device dr shift-dr_value <dr_value>

Performs a DR shift operation.

-length <data register length>-no_captured_dr_value-value_in_hex(1)This argument is optional.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

20

UG-SLDVRTL
2016.10.31

Running a DR Shift Operation Through a Virtual JTAG Chain

Central to Virtual JTAG IP core are the device_virtual_ir_shift and device_virtual_dr_shiftcommands. These commands perform the shift operation to each VIR/VDR and provide the address to
the SLD hub for the active JTAG datapath.
Each device_virtual_ir_shift command issues a USER1 instruction to the JTAG Instruction Register
followed by a DR shift containing the VIR value provided by the ir_value argument prepended byaddress bits to target the correct SLD node instance.
Note: Use the -no_captured_ir_value argument if you do not care about shifting out the contents of thecurrent VIR value. Enabling this argument increases the speed of the VIR shift transaction byeliminating a command cycle within the underlying transaction.
Similarly, each device_virtual_dr_shift command issues a USER0 instruction to the JTAG Instruction
Register followed by a DR shift containing the VDR value provided by the dr_value argument. These
commands return the underlying JTAG transactions with the show_equivalent_device_ir_dr_shiftoption set.
Note: The device_virtual_ir_shift takes the ir_value argument as a numeric value. The
device_virtual_dr_shift takes the dr_value argument by either a binary string or a hexadec‐
imal string. Do not use numeric values for the device_virtual_dr_shift.

Running a DR Shift Operation Through a Virtual JTAG Chain
A simple DR shift operation through a virtual JTAG chain using an Altera download cable consists of thefollowing steps:
1. Query for the Altera programming cable and select the active cable.
2. Target the desired device in the JTAG chain.
3. Obtain a device lock for exclusive communication to the device.
4. Perform a VIR shift.
5. Perform a VDR shift.
6. Release exclusive link with the device with the device_unlock command.
7. Close communication with the device with the close_device command.

Run-Time Communication
The Virtual JTAG IP core Tcl API requires an Altera programming cable. Designs that use a custom
controller to drive the JTAG chain directly must issue the correct JTAG IR/DR transactions to target theVirtual JTAG IP core instances. The address values and register length information for each Virtual JTAG
IP core instance are provided in the compilation reports.
The following figure shows the compilation report for a Virtual JTAG IP core Instance. The following table
describes each column in the Virtual JTAG Settings compilation report.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Run-Time Communication

21

Figure 10: Compilation Report

Table 9: Virtual JTAG Settings Description
Setting

Description

Instance Index

Instance index of the virtual JTAG IP core. Assigned atcompile time.

Auto Index

Details whether the index was auto-assigned.

Index Re-Assigned

Details whether the index was user-assigned.

IR Width

Length of the Virtual IR register for this IP core instance;
defined in theparameter editor.

Address

The address value assigned to the IP core by the compiler.

USER1 DR Length

The length of the USER1 DR register. The USER1 DR
register encapsulates the VIR for all SLD nodes.

VIR Capture Instruction

Instruction value to capture the VIR of this IP core instance.

The Tcl API provides a way to return the JTAG IR/DR transactions by using theshow_equivalent_device_ir_dr_shift argument with the device_virtual_ir_shift anddevice_virtual_dr_shift commands. The following examples use returned values of a virtual IR/DR

shift to illustrate the format of the underlying transactions.
Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

22

UG-SLDVRTL
2016.10.31

Virtual IR/DR Shift Transaction without Returning Captured IR/DR Values

To use the Tcl API to query for the bit pattern in your design, use theshow_equivalent_device_ir_dr_shift argument with the device_virtual_ir_shift anddevice_virtual_dr_shift commands.
Both examples are from the same design, with a single Virtual JTAG instance. The VIR length for thereference Virtual JTAG instance is configured to 3 bits in length.

Virtual IR/DR Shift Transaction without Returning Captured IR/DR Values
VIR shifts consist of a USER1 (0x0E) IR shift followed by a DR shift to the virtual Instruction Register. The
DR Scan shift consists of the value passed by the - dr_value argument. The length and value of the DR
shift is dependent on the number of SLD nodes in your design. This value consists of address bits to the
SLD node instance concatenated with the desired value of the virtual Instruction Register. The addressing
scheme is determined by the Quartus II software during design compilation.
The Tcl command examples below show a VIR/VDR transaction with the no_captured_value option set.
The commands return the underlying JTAG shift transactions that occur.
Virtual IR Shift with the no_captured_value Option
device_virtual_ir_shift -instance_index 0 -ir_value 1 \-no_captured_ir_value -show_equivalent_device_ir_dr_shift ↵Returns:
Info: Equivalent device ir and dr shift commands
Info: device_​ir_​shift -ir_value 14
Info: device_​dr_​shift -length 5 -dr_value 11 -value_in_hex

Virtual DR Shift with the no_captured_value Option
device_virtual_dr_shift -instance_index 0 -length 8 -dr_value \04 -value_in_hex -no_captured_dr_value \-show_equivalent_device_ir_dr_shift ↵Returns:
Info: Equivalent device ir and dr shift commands
Info: device_​ir_​shift -ir_value 12
Info: device_​dr_​shift -length 8 -dr_value 04 -value_in_hex
The VIR value field in the figure below is four bits long, even though the VIR length is configured to be
three bits long, and shows the bit values and fields associated with the VIR/VDR scans. The Instruction
Register length for all Altera FPGAs and CPLDs is 10-bits long. The USER1 value is 0x0E and USER0 value
is 0x0C for all Altera FPGAs and CPLDs. The Address bits contained in the DR scan shift of a VIR scan aredetermined by the Quartus II software.
Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Virtual IR/DR Shift Transaction that Captures Current VIR/VDR Values

23

All USER1 DR chains must be of uniform length. The length of the VIR value field length is determined bylength of the longest VIR register for all SLD nodes instantiated in the design. Because the SLD hub VIR isfour bits long, the minimum length for the VIR value field for all SLD nodes in the design is at least four
bits in length. The Quartus II Tcl API automatically sizes the shift transaction to the correct length. The
length of the VIR register is provided in the Virtual JTAG settings compilation report. If you are driving
the JTAG interface with a custom controller, you must pay attention to size of the USER1 DR chain.
Figure 11: Equivalent Bit Pattern Shifted into Device by VIR/VDR Shift Commands
V irtual IR Scan
IR Scan Shift00

DR Scan ShiftAddr
VIR Value

USER1
0

0

0

0

1

1

1

0

1

0

0

0

1

V irtual DR Scan
IR Scan Shift00

DR Scan Shift

USER0
0

0

0

0

1

1

0

0

0

0

VDR Value
0

0

0

1

0

0

Virtual IR/DR Shift Transaction that Captures Current VIR/VDR Values
The Tcl command examples below show that the no_captured_value option is not set in the Virtual
IR/DR shift commands and the underlying JTAG shift commands associated with each. In the VIR shiftcommand, the command returns two device_dr_shift commands.
Virtual IR Shiftdevice_virtual_ir_shift -instance_index 0 -ir_value 1 \-no_captured_ir_value -show_equivalent_device_ir_dr_shift

Returns:
Info: Equivalent device ir and dr shift commands
Info: device_​ir_​shift -ir_value 14
Info: device_​dr_​shift –length 5 –dr_value 0B –value_in_hex
Info: device_​dr_​shift -length 5 -dr_value 11 -value_in_hex

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

24

UG-SLDVRTL
2016.10.31

Reset Considerations when Using a Custom JTAG Controller

Virtual DR Shiftdevice_virtual_dr_shift -instance_index 0 -length 8 -dr_value \04 -value_in_hex -show_equivalent_device_ir_dr_shift

Returns:
Info: Equivalent device ir and dr shift commands
Info: device_​ir_​shift -ir_value 12
Info: device_​dr_​shift -length 8 -dr_value 04 -value_in_hex
The figure below shows an example of VIR/VDR Shift Commands with captured IR values. DR Scan Shift
1 is the VIR_CAPTURE command, as shown in the figure below. It targets the VIR of the sld_hub. This
command is an address cycle to select the active VIR chain to shift after jtag_state_cir is asserted. The
HUB_FORCE_IR capture must be issued whenever you capture the VIR from a target SLD node that isdifferent than the current active node. DR Scan Shift 1 targets the SLD hub VIR to force a captured value
from Virtual JTAG instance 1 and is shown as the VIR_CAPTURE command. DR Scan Shift 2 targets the
VIR of Virtual JTAG instance.
Figure 12: Equivalent Bit Pattern Shifted into Device by VIR/VDR Shift Commands with Captured IR Values
V irtual IR Scan
IR Scan Shift00

DR Scan Shift 1
Addr
VIR Value

USER1
0

0

0

0

1

1

1

0

0

1

0

1

DR Scan Shift 2
Addr
VIR Value
1

0

1

0

0

1

V irtual DR Scan
IR Scan Shift00

DR Scan Shift

USER0
0

0

0

0

1

1

0

0

0

0

VDR Value
0

0

0

1

0

0

Note: If you use an embedded processor as a controller for the JTAG chain and your Virtual JTAG IP core
instances, consider using the JAM Standard Test and Programming Language (STAPL). JAM
STAPL is an industry-standard flow-control-based language that supports JTAG communicationtransactions. JAM STAPL is open source, with software downloads and source code available fromthe Altera website.
Related Information• ISP & the Jam STAPL• Embedded Programming With Jam STAPL

Reset Considerations when Using a Custom JTAG Controller
The SLD hub decodes TMS independently to determine the JTAG controller state. Under normal operation,
the SLD hub mirrors all of the JTAG TAP controller states accurately. The JTAG pins (TCK, TMS, TDI, andAltera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Instantiating the Virtual JTAG IP Core

25

TDO) are accessible to the core programmable logic; however, the JTAG TAP controller outputs are notvisible to the core programmable logic. In addition, the hard JTAG TAP controller does not use any reset
signals as inputs from the core programmable logic.
This can cause the following two situations in which control states of the SLD hub and the JTAG TAP
controller are not in lock-step:• An assertion of the device wide global reset signal (DEV_CLRn)• An assertion of the TRST signal, if available on the device
DEV_CLRn resets the SLD hub but does not reset the hard TAP controller block. The TAP controller ismeant to be decoupled from USER mode device operation to run boundary scan operations. Asserting the
global reset signal does not disrupt boundary-scan test (BST) operation.

Conversely, the TRST signal, if available, resets the JTAG TAP controller but does not reset the SLD hub.
The TRST signal does not route into the core programmable logic of the PLD.
To guarantee that the states of the JTAG TAP controller and the SLD hub state machine are properly
synchronized, TMS should be held high for at least five clock cycles after any intentional reset of either the
TAP controller or the system logic. Both the JTAG TAP controller and the sld_hub controller are
guaranteed to be in the Test Logic Reset state after five clock cycles of TMS held high.

Instantiating the Virtual JTAG IP CoreTo create the Virtual JTAG IP core in a Quartus II design requires the following system and software
requirements:• The Quartus II software• An Altera download cable, such as a USB-Blaster cable
The download cable is required to communicate with the Virtual JTAG IP core from a host running thequartus_stp executable.

IP Catalog and Parameter Editor
The IP Catalog displays the IP cores available for your project. Use the following features of the IP Catalog
to locate and customize an IP core:• Filter IP Catalog to Show IP for active device family or Show IP for all device families. If you have no
project open, select the Device Family in IP Catalog.
• Type in the Search field to locate any full or partial IP core name in IP Catalog.
• Right-click an IP core name in IP Catalog to display details about supported devices, to open the IP
core's installation folder, and for links to IP documentation.
• Click Search for Partner IP to access partner IP information on the web.
The parameter editor prompts you to specify an IP variation name, optional ports, and output file
generation options. The parameter editor generates a top-level IP file (.ip) for an IP variation in projects.
The parameter editor generates a top-level Quartus IP file (.qip) for an IP variation in projects. Thesefiles represent the IP variation in the project, and store parameterization information.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

26

UG-SLDVRTL
2016.10.31

The Parameter Editor

Figure 13: IP Parameter Editor ()View IP Portand Parameter
Details

Specify IP Variation
Name and Target Device

For Qsys Pro Systems Only

Apply Preset Parameters forSpecific Applications

The Parameter Editor

The parameter editor helps you to configure IP core ports, parameters, and output file generation options.
The basic parameter editor controls include the following:

Use the Presets window to apply preset parameter values for specific applications (for select cores).
Use the Details window to view port and parameter descriptions, and click links to documentation.
Click Generate > Generate Testbench System to generate a testbench system (for select cores).
Click Generate > Generate Example Design to generate an example design (for select cores).
Click Validate System Integrity to validate a system's generic components against companion files.
(Qsys Pro systems only)• Click Sync All System Infos to validate a system's generic components against companion files. (Qsys
Pro systems only)
•
•
•
•
•

The IP Catalog is also available in Qsys and Qsys Pro (View > IP Catalog). The Qsys IP Catalog includes
exclusive system interconnect, video and image processing, and other system-level IP that are not available
in the IP Catalog. Refer to Creating a System with Qsys Pro or Creating a System with Qsys for information
on use of IP in Qsys and Qsys Pro, respectively.
Related Information• Creating a System with Qsys Pro

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Specifying IP Core Parameters and Options

27• Creating a System with Qsys

Specifying IP Core Parameters and Options
Follow these steps to specify IP core parameters and options.
1. In the Qsys IP Catalog (Tools > IP Catalog), locate and double-click the name of the IP core tocustomize. The parameter editor appears.
2. Specify a top-level name for your custom IP variation. This name identifies the IP core variation files inyour project. If prompted, also specify the target FPGA device family and output file HDL preference.
Click OK.
3. Specify parameters and options for your IP variation:• Optionally select preset parameter values. Presets specify all initial parameter values for specificapplications (where provided).
• Specify parameters defining the IP core functionality, port configurations, and device-specificfeatures.
• Specify options for generation of a timing netlist, simulation model, testbench, or example design(where applicable).
• Specify options for processing the IP core files in other EDA tools.
4. Click Finish to generate synthesis and other optional files matching your IP variation specifications.
The parameter editor generates the top-level .qsys IP variation file and HDL files for synthesis andsimulation. Some IP cores also simultaneously generate a testbench or example design for hardware
testing.
5. To generate a simulation testbench, click Generate > Generate Testbench System. Generate
Testbench System is not available for some IP cores that do not provide a simulation testbench.
6. To generate a top-level HDL example for hardware verification, click Generate > HDL Example.
Generate > HDL Example is not available for some IP cores.
The top-level IP variation is added to the current project. Click Project > Add/Remove Files in Project tomanually add a .qsys file to a project. Make appropriate pin assignments to connect ports.

Files Generated for Altera IP Cores (Legacy Parameter Editor)

The Quartus II software version generates the following output for your IP core that uses the legacy
parameter editor.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

28

UG-SLDVRTL
2016.10.31

Files Generated for Altera IP Cores (Legacy Parameter Editor)

Figure 14: IP Core Generated Files<Project Directory><your_ip>.qip or .qsys - System or IP integration file
<your_ip>.sopcinfo - Software tool-chain integration file
<your_ip> - IP core variation files<your_ip>_bb.v - Verilog HDL black box EDA synthesis file
<your_ip>_inst.v or .vhd - Sample instantiation template<your_ip>_generation.rpt - IP generation report<your_ip>.bsf - Block symbol schematic file
<your_ip>.ppf - XML I/O pin information file

<your_ip>.spd - Combines individual simulation startup scripts 1<your_ip>_syn.v or .vhd - Timing & resource estimation netlist 1<your_ip>.html - Contains memory map
simulation - IP simulation files<your_ip>.sip - NativeLink simulation integration file
<your_ip>.v, .vhd, .vo, .vho - HDL or IPFS models2<simulator vendor> - Simulator setup scripts<simulator_setup_scripts>
synthesis - IP synthesis files<your_ip>.qip - Lists files for synthesis<your_ip>.debuginfo - Lists files for synthesis<your_ip>.v or .vhd - Top-level IP variation synthesis file
testbench - Simulation testbench files 1<testbench_hdl_files><simulator_vendor> - Testbench for supported simulators<simulation_testbench_files><your_ip>_tb - Testbench for supported simulators<your_ip>_tb.v or .vhd - Top-level HDL testbench file

Notes:
1. If supported and enabled for your IP variation
2. If functional simulation models are generated

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Instantiating Directly in HDL

29

Instantiating Directly in HDL
To properly connect the Virtual JTAG IP core in your design, follow these basic connection rules:• The tck output from the Virtual JTAG IP core is the clock used for shifting the data in and out on the
TDI and TDO pins.
• The TMS output of the Virtual JTAG IP core reflects the TMS input to the main JTAG circuit.
• The ir_in output port of the Virtual JTAG IP core is the parallel output of the contents that get shifted
into the virtual IR of the Virtual JTAG instance. This port is used for decoding logic to select the active
virtual DR chain.
The purpose of instantiating a Virtual JTAG instance in this example is to load my_counter through the
JTAG port using a software application built with Tcl commands and the quartus_stp executable. In thisdesign, the Virtual JTAG instance is called my_vji. Whenever a Virtual JTAG IP core is instantiated in adesign, three logic blocks are usually needed: a decode logic block, a TDO logic block, and a Data Register
block. The example below combines the Virtual JTAG instance, the decode logic, the TDO logic and theData Register blocks.
You can use the following Verilog HDL template as a guide for instantiating and connecting various
signals of the IP cores in your design.
modulecounter (clock, my_counter);
input
clock;
output [3:0] my_counter;reg [3:0]
my_counter;always @ (posedge clock)
if (load && e1dr) // decode logic: used to load the counter my_countermy_counter <= tmp_reg;
else
my_counter <= my_counter + 1;// Signals and registers declared for VJI instancewire tck, tdi;
reg tdo;wire cdr, eldr, e2dr, pdr, sdr, udr, uir, cir;wire [1:0] ir_in;// Instantiation of VJI
my_vji VJI_INST(.tdo (tdo),.tck (tck),.tdi (tdi),.tms(),.ir_in(ir_in),.ir_out(),.virtual_state_cdr (cdr),.virtual_state_e1dr(e1dr),.virtual_state_e2dr(e2dr),.virtual_state_pdr (pdr),.virtual_state_sdr (sdr),.virtual_state_udr (udr),.virtual_state_uir (uir),.virtual_state_cir (cir));// Declaration of data registerreg [3:0] tmp_reg;// Deocde Logic Block// Making some decode logic from ir_in output port of VJI
wire load = ir_in[1] && ~ir_in[0];// Bypass used to maintain the scan chain continuity for// tdi and tdo ports
bypass_reg <= tdi;
Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

30

Simulation Support

UG-SLDVRTL
2016.10.31// Data Register Blockalways @ (posedge tck)
if ( load && sdr )tmp_reg <= {tdi, tmp_reg[3:1]};// tdo Logic Blockalways @ (tmp_reg[0] or bypass_reg)
if(load)tdo <= tmp_reg[0]elsetdo <= bypass_reg;
endmodule

The decode logic is produced by defining a wire load to be active high whenever the IR of the Virtual
JTAG IP core is 01. The IR scan shift is used to load the data into the IR of the Virtual JTAG IP core. The
ir_in output port reflects the IR contents.
The Data Register logic contains a 4-bit shift register named tmp_reg. The always blocks shown for the
Data Register logic also contain the decode logic consisting of the load and sdr signals. The sdr signal is
the output of the Virtual JTAG IP core that is asserted high during a DR scan shift operation. The time
during which the sdr output is asserted high is the time in which the data on tdi is valid. During thattime period, the data is shifted into the tmp_reg shift register. Therefore, tmp_reg gets the data from the
Virtual JTAG IP core on the tdi output port during a DR scan operation.
There is a 1-bit register named bypass_reg whose output is connected with tdo logic to maintain thecontinuity of the scan chain during idle or IR scan shift operation of the Virtual JTAG IP core. The tdo
logic consists of outputs coming from tmp_reg and bypass_reg and connecting to the tdo input of the
Virtual JTAG IP core. The tdo logic passes the data from tmp_reg to the Virtual JTAG IP core during DR
scan shift operations.
The always block of a 4-bit counter also consists of some decode logic. This decode logic uses the load
signal and e1dr output signal of the Virtual JTAG IP core to load the counter with the contents of
tmp_reg. The Virtual JTAG output signal e1dr is asserted high during a DR scan shift operation when all
the data is completely shifted into the tmp_reg and sdr has been de-asserted. In addition to sdr and e1dr,
there are other outputs from the Virtual JTAG IP core that are asserted high to show various states of the
TAP controller and internal states of the Virtual JTAG IP core. All of these signals can be used to performdifferent logic operations as needed in your design.

Simulation Support
Virtual JTAG interface operations can be simulated using all Altera-supported simulators. The simulation
support is for DR and IR scan shift operations. For simulation purposes, a behavioral simulation model ofthe IP core is provided in both VHDL and Verilog HDL in the altera_mf libraries. The I/O structure of themodel is the same as the IP core.
In its implementation, the Virtual JTAG IP core connects to your design on one side and to the JTAG port
through the JTAG hub on the other side. However, a simulation model connects only to your design. Thereis no simulation model for the JTAG circuit. Therefore, no stimuli can be provided from the JTAG ports ofthe device to imitate the scan shift operations of the Virtual JTAG IP core in simulation.
The scan operations in simulation are realized using the simulation model. The simulation model consistsof a signal generator, a model of the SLD hub, and the Virtual JTAG model. The stimuli defined in the
wizard are passed as parameters to this simulation model from the variation file. The simulation
parameters are listed in the table below. The signal generator then produces the necessary signals for
Virtual JTAG IP core outputs such as tck, tdi, tms, and so forth.
Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Simulation Support

31

The model is parameterized to allow the simulation of an unlimited number of Virtual JTAG instances.
The parameter sld_sim_action defines the strings used for IR and DR scan shifts. Each Virtual JTAG’svariation file passes these parameters to the Virtual JTAG component. The Virtual JTAG’s variation file canalways be edited for generating different stimuli, though the preferred way to specify stimuli for DR and IR
scan shifts is to use the parameter editor.
Note: To perform functional and timing simulations, you must use the altera_mf.v library located in the<Quartus II installation directory>\eda\sim_lib directory. For VHDL, you must use thealtera_mf.vhd library located in the <Quartus II installation directory>\eda\sim_lib directory.
The VHDL component declaration file is located in the altera_mf_components.vhd library in the<Quartus II installation directory>\eda\sim_lib directory.
Table 10: Description of Simulation Parameters
Parameter

Comments

SLD_SIM_N_SCAN

Specifies the number of shifts in the simulation model.

SLD_SIM_TOTAL_LENGTH

The total number of bits to be shifted in either an IR shift or a DR
shift. This value should be equal to the sum of all the length
values specified in the SLD_SIM_ACTION string.

SLD_SIM_ACTION

Specifies the strings used for instruction register (IR) and dataregister (DR) scan shifts. The string has the following format:((time,type,value,length),(time,type,value,length),...
(time,type,value,length))where:• time—A 32-bit value in milliseconds that represents the start
time of the shift relative to the completion of the previous shift.
• type—A 4-bit value that determines whether the shift is a DR
shift or an IR shift.
• value—The data associated with the shift. For IR shifts, it is a
32-bit value. For DR shifts, the length is determined by length.
• length—A 32-bit value that specifies the length of the data
being shifted. This value should be equal to SLD_NODE_IR_
WIDTH; otherwise, the value field may be padded or truncated. 0
is invalid.
Entries are in hexadecimal format.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

32

Simulation Support

UG-SLDVRTL
2016.10.31

Simulation has the following limitations:• Scan shifts (IR or DR) must be at least 1 ms apart in simulation time.
• Only behavioral or functional level simulation support is present for this IP core. There is no gate levelor timing level simulation support.
• For behavioral simulation, the stimuli tell the signal generator model in the Virtual JTAG model togenerate the sequence of signals needed to produce the necessary outputs for tck, tms, tdi, and soforth. You cannot provide the stimulus at the JTAG pins of the device.
• The tck clock period used in simulation is 10 MHz with a 50% duty cycle. In hardware, the period of
the tck clock cycle may vary.
• In a real system, each instance of the Virtual JTAG IP core works independently. In simulation,
multiple instances can work at the same time. For example, if you define a scan shift for Virtual JTAG
instance number 1 to happen at 3 ms and a scan shift for Virtual JTAG instance number 2 to happen at
the same time, the simulation works correctly.
If you are using the ModelSim-Altera simulator, the altera_mf.v and altera_mf.vhd libraries are provided
in precompiled form with the simulator.
The inputs and outputs of the Virtual JTAG IP core during a typical IR scan shift operation are shown in
the figure below.
Figure 15: IR Shift Waveform

The figure below shows the inputs and outputs of the Virtual JTAG IP core during a typical DR scan shiftoperation.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Compiling the Design

33

Figure 16: DR Shift Waveform

Compiling the Design
You can instantiate a maximum of 128 instances of the Virtual JTAG IP core in a design. Aftercompilation, each instance has a unique ID, as shown on the Virtual JTAG Settings page of the Analysis &Synthesis section of the Compilation Report, as shown in the figure below.
Figure 17: IDs of Virtual JTAG Instances

ID of sid_virtual_jtag
instances

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

34

Third-Party Synthesis Support

UG-SLDVRTL
2016.10.31

These unique IDs are necessary for Quartus II Tcl API to properly address each instance of the IP core.
The addition of Virtual JTAG IP cores uses logic resources in your design. The Fitter Resource Section in
the Compilation Report shows the logic resource utilization, as shown in the figure below.
Figure 18: Logic Resources Utilized

sld_virtual_jtag
instances

Related Information• Design Implementation and Optimization• Verification

Third-Party Synthesis Support
In addition to the variation file, the parameter editor creates a black box file for the Virtual JTAG IP core
you created.
For example, if you create a my_vji.v file, a my_vji_bb.v file is also created. In third-party synthesis, you
include this black box file with your design files to synthesize your project. A VQM file is usually producedby third-party synthesis tools. This VQM netlist and the Virtual JTAG IP core’s variation files are input tothe Quartus II software for further compilation.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

SLD_NODE Discovery and Enumeration

35

SLD_NODE Discovery and Enumeration
You can use a custom JTAG controller to discover transactions necessary to enumerate all Virtual JTAG IP
core instances from your design at runtime. All SLD nodes and the virtual JTAG registers that they
contain are targeted by two Instruction Register values, USER0 and USER1, which are shown in the tablebelow.
Table 11: USER1 and USER2 Instruction Values
Instruction

Binary Pattern

USER0

00 0000 1100

USER100 0000 1110

The USER1 instruction targets the virtual IR of either the sld_hub or a SLD node. That is, when the USER1
instruction is issued to the device, the subsequent DR scans target a specific virtual IR chain based on an
address field contained within the DR scan. The table below shows how the virtual IR, the DR target of the
USER1 instruction is interpreted.
The VIR_VALUE in the table below is the virtual IR value for the target SLD node. The width of this field ism bits in length, where m is the length of the largest VIR for all of the SLD nodes in the design. All SLD
nodes with VIR lengths of fewer than m bits must pad VIR_VALUE with zeros up to a length of m.
Table 12: USER1 DR
m+n–1

m

ADDR [(n – 1)..0]m–1

0

VIR_VALUE [(m – 1)..0]

The ADDR bits act as address values to signal the active SLD node that the virtual IR shift targets. ADDR is n
bits in length, where n bits must be long enough to encode all SLD nodes within the design, as shown
below.
n = CEIL(log2(Number of SLD_nodes +1))

The SLD hub is always 0 in the address map, as shown below.
ADDR[(n -1)..0] = 0

Discovery and enumeration of the SLD instances within a design requires interrogation of the sld_hub todetermine the dimensions of the USER1 DR (m and n) and associating each SLD instance, specifically the
Virtual JTAG IP core instances, with an address value contained within the ADDR bits of the USER1 DR.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

36

UG-SLDVRTL
2016.10.31

Issuing the HUB_INFO Instruction

The discovery and enumeration process consists of the following steps:
1. Interrogate the SLD hub with the HUB_INFO instruction.
2. Shift out the 32-bit HUB IP Configuration Register to determine the number of SLD nodes in thedesign and the dimensions of the USER1 DR.
3. Associate the Virtual JTAG instance index to an ADDR value by shifting out the 32-bit SLD node info
register for each SLD node in the design.

Issuing the HUB_INFO Instruction
The SLD hub contains the HUB IP Configuration Register and SLD_NODE_INFO register for each SLD nodein the design. The HUB IP configuration register provides information needed to determine thedimensions of the USER1 DR chain.
The SLD_NODE_INFO register is used to determine the address mapping for Virtual JTAG instance in yourdesign. This register set is shifted out by issuing the HUB_INFO instruction. Both the ADDR bits for the SLD
hub and the HUB_INFO instruction is 0 × 0.
Because m and n are unknown at this point, the DR register (ADDR bits + VIR_VALUE) must be filledwith zeros. Shifting a sequence of 64 zeroes into the USER1 DR is sufficient to cover the most conservative
case for m and n.

HUB IP Configuration Register
When the USER1 and HUB_INFO instruction sequence is issued, the USER0 instruction must be applied toenable the target register of the HUB_INFO instruction.
The HUB IP configuration register is shifted out using eight four-bit nibble scans of the DR register. Eachfour-bit scan must pass through the UPDATE_DR state before the next four-bit scan. The 8 scans areassembled into a 32-bit value with the definitions shown in the table below.
Table 13: Hub IP Configuration Register
Nibble731

Nibble627

Nibble526

HUB IP version

Nibble4

19
N

18

Nibble3

Nibble2

8

ALTERA_MFG_ID (0 × 06E)

Nibble1Nibble070m

The dimensions of the USER1 DR chain can be determined from the SUM (m, n) and N (number of nodes
in the design). The equations below shows the values of m and n.
n = CEIL(log2(N+1))
m = SUM(m,n) – n

SLD_NODE Info Register
When the number of SLD nodes is known, the nodes on the hub can be enumerated by repeating the 8four-bit nibble scans, once for each Node, to yield the SLD_NODE_INFO register of each node.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

37

Capturing the Virtual IR Instruction Register

The DR nibble shifts are a continuation of the HUB_INFO DR shift used to shift out the Hub IP Configura‐tion register.
The order of the Nodes as they are shifted out determines the ADDR values for the Nodes, beginning with,for the first Node SLD_NODE_INFO shifted out, up to and including, for the last node on the hub. The tables
below show the SLD_NODE_INFO register and their functional descriptions.
Table 14: SLD_NODE_INFO Register31

27

Node Version

26

19

NODE ID

18

8

NODE MFG_ID

70

NODE_INST_ID

Table 15: SLD_NODE_INFO Register Descriptions
Field

Function

Node Version

Identifies the version of the SLD node

NODE ID

Identifies the type of NODE IP (0x8 for the Virtual JTAG IP core)

NODE MFG_ID

SLD Node Manufacturer ID (0x6E for Virtual JTAG IP core)

NODE_INST_ID

Used to distinguish multiple instances of the same IP. Corresponds tothe instance index assigned in the parameter editor.

You can identify each Virtual JTAG instance within the design by decoding NODE ID and NODE_INST_ID.
The Virtual JTAG IP core uses a NODE ID of 8. The NODE_INST_ID corresponds to the instance index thatyou configured within the parameter editor. The ADDR bits for each Virtual JTAG node is then determinedby matching each Virtual JTAG instance to the sequence number in which the SLD_NODE_INFO register isshifted out.

Capturing the Virtual IR Instruction Register
In applications that contain multiple nodes, capturing the value of the VIR may require issuing an
instruction to the SLD hub to target a SLD node. You can query for a VIR using the VIR_CAPTURE
instruction.
Each NODE VIR register acts as a parallel hold rank register to the USER1 DR chain. The sld_hub uses thebits prepended to the VIR shift value to target the correct SLD NODE VIR register. After the
SLD_state_machine asserts virtual_update_IR, the active SLD node latches VIR_VALUE of the USER1DR register.
The figure below shows a functional model of the interaction of the USER1 DR register and the SLD node
VIR. The ADDR bits target the selection muxes in the figure after the sld_hub FSM has exited thevirtual_update_IR state. Upon the next USER1 DR transaction, the USER1 DR chain will latch the VIRof the last active SLD_NODE to shift out of TDO. Thus, if you need to capture the VIR of an SLD node that
Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

38

UG-SLDVRTL
2016.10.31

AHDL Function Prototype

is different than the one addressed in the previous shift cycle, you must issue the VIR_CAPTURE instruction.
The VIR_CAPTURE instruction to the sld_hub acts as an address cycle to force an update to the muxes.
Figure 19: Functional Model Interaction between USER1 DR CHAIN and SLD Node VIRs
USER1 DRTDIADDR[n - 1..0]

VIR_value

msb

TDO
lsb

N

SLD NODEVIR2SLD NODEVIR

1

ADDR[n - 1..0]

SLD NODEVIR

SLD Nodes

ADDR[n - 1..0]

To form the VIR_CAPTURE instruction, use the following instruction format:
VIR_CAPTURE = ZERO [ (m – 4)..0] ## ADDR [(n – 1)..0] ## 011

In this format, ZERO[] is an array of zeros, ## is the concatenation operator, m is the width of VIR_VALUE,
and n is the width of the ADDR bit.

AHDL Function Prototype
The following AHDL function prototype is located in the sld_virtual_jtag.inc file in the <Quartus II
installation directory> \libraries\megafunctions directory.
Note: Port name and order also apply to Verilog HDL.
FUNCTION sld_virtual_jtag(
ir_out[sld_ir_width-1..0],
tdo
)
WITH(
lpm_hint,
lpm_type,
sld_auto_instance_index,
sld_instance_index,

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

VHDL Component Declaration

39

sld_ir_width,sld_sim_action,
sld_sim_n_scan,
sld_sim_total_length)
RETURNS(
ir_in[sld_ir_width-1..0],
jtag_state_cdr,
jtag_state_cir,
jtag_state_e1dr,
jtag_state_e1ir,
jtag_state_e2dr,
jtag_state_e2ir,
jtag_state_pdr,
jtag_state_pir,
jtag_state_rti,
jtag_state_sdr,
jtag_state_sdrs,
jtag_state_sir,
jtag_state_sirs,
jtag_state_tlr,
jtag_state_udr,
jtag_state_uir,
tck,
tdi,
tms,
virtual_state_cdr,
virtual_state_cir,
virtual_state_e1dr,
virtual_state_e2dr,
virtual_state_pdr,
virtual_state_sdr,
virtual_state_udr,
virtual_state_uir);

VHDL Component Declaration
The following VHDL component declaration is located in the ALTERA_MF_COMPONENTS.vhd filelocated in the <Quartus II installation directory>\libraries\vhdl\altera_mf directory.
component sld_virtual_jtag
generic (lpm_hint:
string := "UNUSED";
lpm_type:
string := "sld_virtual_jtag";
sld_auto_instance_index :string := "NO";
sld_instance_index:
natural := 0;
sld_ir_width:
natural := 1;
sld_sim_action :string := "UNUSED";
sld_sim_n_scan :natural := 0;
sld_sim_total_length:
natural := 0 );port(
ir_in : out std_logic_vector(sld_ir_width-1 downto 0);
ir_out: in std_logic_vector(sld_ir_width-1 downto 0);
jtag_state_cdr :out std_logic;
jtag_state_cir :out std_logic;
jtag_state_e1dr :out std_logic;
jtag_state_e1ir :out std_logic;
jtag_state_e2dr :out std_logic;
jtag_state_e2ir :out std_logic;
jtag_state_pdr :out std_logic;
jtag_state_pir :out std_logic;
jtag_state_rti :out std_logic;
Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

40

UG-SLDVRTL
2016.10.31

VHDL LIBRARY-USE Declaration
jtag_state_sdr :out std_logic;
jtag_state_sdrs :out std_logic;
jtag_state_sir :out std_logic;
jtag_state_sirs :out std_logic;
jtag_state_tlr :out std_logic;
jtag_state_udr :out std_logic;
jtag_state_uir :out std_logic;tck:
out std_logic;
tdi:
out std_logic;
tdo:
in std_logic;
tms:
out std_logic;
virtual_state_cdr:
out std_logic;
virtual_state_cir:
out std_logic;
virtual_state_e1dr:
out std_logic;
virtual_state_e2dr:
out std_logic;
virtual_state_pdr:
out std_logic;
virtual_state_sdr:
out std_logic;
virtual_state_udr:
out std_logic;
virtual_state_uir:
out std_logic);
end component;

VHDL LIBRARY-USE Declaration
The VHDL LIBRARY-USE declaration is not required if you use the VHDL Component Declaration.
LIBRARY altera_mf;
USE altera_mf.altera_mf_components.all;

Design Example: TAP Controller State Machine
The TAP controller is a state machine with a set of control signals that routes TDI data between theInstruction Register and the bank of DR chains. It controls the start and stop of any shift transactions, andcontrols the data flow between the parallel hold registers and the shift registers of the Instruction Registerand the Data Register. The TAP controller is controlled by the TMS pin.
The figure below shows the TAP controller state machine. The table that follows provides a description ofeach of the states.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Design Example: TAP Controller State Machine

41

Figure 20: JTAG TAP Controller State Machine

TMS = 1

TEST_LOGIC/RESETTMS = 0

TMS = 0

RUN_TEST/IDLE

TMS = 1TMS = 1

SELECT_
DR_SCANTMS = 1

SELECT_
IR_SCANTMS = 0
TMS = 1TMS = 0
TMS = 1CAPTURE_DR

CAPTURE_IR

TMS = 0

TMS = 0SHIFT_DR

SHIFT_IR
TMS = 0

TMS = 0
TMS = 1TMS = 1
EXIT1_DR

TMS = 1

EXIT1_IR

TMS = 0

TMS = 0
PAUSE_DR

PAUSE_IR
TMS = 0

EXIT2_DR

TMS = 0

EXIT2_IR

TMS = 1TMS = 1TMS = 1TMS = 0
TMS = 1TMS = 1TMS = 0

TMS = 1UPDATE_DR
TMS = 0

TMS = 1UPDATE_IR
TMS = 0

Table 16: Functional Description for the TAP Controller States
TAP Controller State

Functional Description

Test-Logic-Reset

The test logic of the JTAG scan chain is disabled.

Run-Test/Idle

This is a hold state. Once entered, the controller remains inthis state as long as TMS is held low.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

42

UG-SLDVRTL
2016.10.31

Design Example: Modifying the DCFIFO Contents at Runtime

TAP Controller State

Functional Description

Select DR-Scan/Select IR Scan

These are temporary controller states. A decision is madehere whether to enter the DR states or the IR states.

Capture DR/Capture IR

These states enable a parallel load of the shift registers fromthe hold registers on the rising edge of TCK.

Shift DR/​Shift IR

These states enable shifting of the DR and IR chains.

Exit1 DR/Exit1 IR

Temporary hold states. A decision is made in these states toeither advance to the Update states or the Pause states.

Pause DR/Pause IRThis controller state allows shifting of the Instruction
Register and Data Register to be temporarily halted.

Exit2 DR/Exit2 IR

Temporary hold states. A decision is made in these states toadvance to the Update states.

Update DR/Update IR

These states enable a parallel load of the hold registers fromthe shift registers. Update happens on the falling edge of
TCK.

Design Example: Modifying the DCFIFO Contents at Runtime
This design example demonstrates the use of the Virtual JTAG IP core and a command-line script todynamically modify the contents of a DCFIFO at runtime.
The Tcl API that ships with the Virtual JTAG IP core makes it an ideal solution for developing
command-line scripts that can be used to either update data values or toggle control bits at run time. Thisvisibility into the FPGA can help expedite debug closure during the prototyping phase of the design,especially when external equipment is not available to provide a stimulus.
This design example consists of a Quartus II project file that implements a DCFIFO and a command-line
script that is used to modify the contents of the FIFO at runtime.
The RTL consists of a single instantiation of the Virtual JTAG IP core to communicate with the JTAG
circuitry. Both read and write ports of the DCFIFO are clocked at 50 MHz. A SignalTap II Logic Analyzer
instance taps the data output bus of the DCFIFO to read burst transactions from the DCFIFO. The
following sections discuss the RTL implementation and the runtime control of the DCFIFO using the Tcl
API.

Write Logic
The RTL uses a single instance of the Virtual JTAG IP core to decode both the instructions for the write
side and read side logic. The IR register is three bits wide, with the three instructions decoded in the RTL,
as shown in the table below.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Read Logic

43

Table 17: Instruction Register Values
Instruction Register Value

Function

PUSH

Instruction to write a single value to the write side logic of the
DCFIFO.

POP

Instruction to read a single value from the read side logic of the
DCFIFO

FLUSH

Instruction to perform a burst read transaction from the FIFO until
empty.

The IR decode logic shifts the Push_in virtual DR chain when the PUSH instruction is on the IR port andvirtual_state_sdr is asserted. A write enable pulse, synchronized to the write_clock, asserts after thevirtual_state_udr signal goes high. The virtual_state_udr signal guarantees stability from the virtual
DR chain. The figure below shows the write side logic for the DCFIFO.
Figure 21: Write Side Logic for DCFIFO
VJI InstanceIR_register

TDO

State
Information

IR Decode/State
Decode Logic

DCFIFOW rite_req

V irtual_DR(Push_in)

TDI

Data[7:0]
W rite_clock
Read_req
Q[7:0]

Data_out

Rd_empty
Read_clock

Read Logic
Two runtime instructions read the contents out of the FIFO. The IR decode logic selects the Push_out
virtual DR chain and generates a single read pulse to the read logic when the POP instruction is active.
The Push_out DR chain is parallel loaded upon the assertion of virtual_state_cdr and shifted out to
TDO upon the assertion of virtual_state_sdr.
When the FLUSH instruction is shifted into the Virtual JTAG instance, the IR decode logic asserts theread_req line until the FIFO is empty. The bypass register is selected when the FLUSH instruction is active
to maintain TDI-to-TDO connectivity. The figure below shows the read side logic for the DCFIFO.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

44

UG-SLDVRTL
2016.10.31

Runtime Communication

Figure 22: Read Side Logic for DCFIFO Design Example
W rite_req

VJI Instance

Data[7:0]
IR_register
State
Information

TDO

W rite_clock

IR Decode/State
Decode Logic

Read_req

Data_out

Q[7:0]
Rd_empty

TDO

Read_clock

V irtual DR(Push_out)

Signal Tap II
Embedded Logic
Analyzer

Runtime Communication
The Tcl script, dc_fifo_vji.tcl, contains three procedures, each corresponding to one of the virtual
JTAG instructions. The table below describes each of the procedures.
Table 18: Run-Time Communication Tcl Procedures
Procedure

Description

push [value]

IR shift the PUSH instruction, followed by a DR shift of the value
argument. Value must be an integer less than 256.

pop

IR shift the POP instruction, followed by a DR shift of 8 bits.

flushfifo

IR shift the FLUSH instruction.

The figure below shows runtime execution of eight values pushed into the DCFIFO and a flushfifocommand, and a SignalTap II Logic Analyzer capture triggering on a flush operation.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Runtime Communication

45

Figure 23: Runtime Execution

Figure 24: SignalTap II Logic Analyzer Capture Triggering on a Flush Operation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation

46

UG-SLDVRTL
2016.10.31

Design Example: Offloading Hardwired Revision Information

Design Example: Offloading Hardwired Revision Information
This example demonstrates how you can use a GUI to offload revision information that is hardwired into adesign. The GUI offloads the time that the design was compiled, the USERCODE from the device, andcompile number that tracks the number of compile iterations that have been performed.
Because the Quartus II software ships with an installation of Tcl/Tk, you can use the Tk package to build acustom GUI to interact with your design. In many cases, the JTAG port is a convenient interface to use,since it is present in most designs for debug purposes. By leveraging Tk and the virtual JTAG interface,
you perform rapid prototyping such as creating virtual front panels or creating simple software applica‐
tions. The figure below shows the organization of the design.
Figure 25: Design Organization Example

Top-Level Design

USERCODE

J TAG

VJI

VersionControl
Information

A Tcl script creates and updates the verilog file containing the hardcoded version control information
every time the project goes through a full compile. The Tcl script is executed automatically by adding thefollowing assignment to the project’s .qsf file.
The USERCODE value shifted out by this design example is a user-configurable 32-bit JTAG register. Thisvalue is configured in the Quartus II software using the Device and Pin Options dialog box.

Configuring the JTAG User Code Setting
The following steps describe how to configure the JTAG User Code setting. A separate script generates the
GUI and is executed with the quartus_stp command line executable. During runtime, the GUI queries
the device for the version information and formats it for display within the message box.
1. On the Assignment menu, click Settings.
2. On the Settings page, in the Category list, click Device.
3. The Device dialog box appears. Click Device and Pin Options.
4. In the Device and Pin Options dialog box, on the General tab, the JTAG user code appears. Type theuser code in 32-bit hexadecimal format.
5. Click OK.

Altera Corporation

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

UG-SLDVRTL
2016.10.31

Document Revision History

47

Related Information

Tcl Example Scripts: Automatic Version Number

Document Revision History
Table 19: Document Revision History
Date

VersionChanges

October 20162016.10.31

Removed Upgrading IP Cores section.

November 2015

2015.11.20

Corrected the flow for EXIT2_DR to SHIFT_DR in the JTAGTAP Controller State Machine figure.

July 20142014.07.08• Replaced MegaWizard Plug-In Manager information withIP Catalog.
• Added standard information about upgrading IP cores.
• Added standard installation and licensing information.
• Removed outdated device support level information. IP coredevice support is now available in IP Catalog and parameter
editor.

March 20142014.03.19

Updated the description of the SLD_IR_WIDTH parameter inthe "Parameters for the Virtual JTAG Megafunction" table.

February 20142014.02.25• Added Document Revision History table.
• Updated "Hub IP Configuration Register" figure.

Altera Virtual JTAG (altera_virtual_jtag) IP Core User Guide
Send Feedback

Altera Corporation