# Patent

## Title
Apparatus and method for trace stream identification of multiple target processor events

## Abstract

When a plurality of simultaneous, preselected target processor events are detected, a multiple-event sync marker is generated that identifies the preselected events and relates the occurrence of these events to timing trace stream. The sync marker for the plurality of preselected events differs from a single event sync marker by including at least one additional packet. The additional packet includes logic signals stored at locations related to each identified event.

## Background
This application claims priority under 35 USC §119 (e) (1) of Provisional Application No. 60/434,174 (TI-34671P) filed Dec. 17, 2002.
RELATED APPLICATIONS 
U.S. patent application Ser. No. 10/728,627, entitled APPARATUS AND METHOD FOR SYNCHRONIZATION OF TRACE STREAMS FROM MULTIPLE PROCESSING UNITS, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,212 entitled APPARATUS AND METHOD FOR SEPARATING DETECTION AND ASSERTION OF A TRIGGER EVENT, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,239, entitled APPARATUS AND METHOD FOR STATE SELECTABLE TRACE STREAM GENERATION, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,650, entitled APPARATUS AND METHOD FOR SELECTING PROGRAM HALTS IN AN UNPROTECTED PIPELINE AT NON-INTERRUPTIBLE POINTS IN CODE EXECUTION, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,591, entitled APPARATUS AND METHOD FOR REPORTING PROGRAM HALTS IN AN UNPROTECTED PIPELINE AT NON-INTERRUPTIBLE POINTS IN CODE EXECUTION, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,407, entitled APPARATUS AND METHOD FOR A FLUSH PROCEDURE IN AN INTERRUPTED TRACE STREAM, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,564, entitled APPARATUS AND METHOD FOR CAPTURING AN EVENT OR COMBINATION OF EVENTS RESULTING IN A TRIGGER SIGNAL IN A TARGET PROCESSOR, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,400, entitled APPARATUS AND METHOD FOR CAPTURING THE PROGRAM COUNTER ADDRESS ASSOCIATED WITH A TRIGGER SIGNAL IN A TARGET PROCESSOR, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,592, entitled APPARATUS AND METHOD DETECTING ADDRESS CHARACTERISTICS FOR USE WITH A TRIGGER GENERATION UNIT IN A TARGET PROCESSOR, invented by Gary L. Swoboda and Jason L. Peck, filed on even date herewith, and assigned to the assignee of the present application U.S. patent application Ser. No. 10/729,639, entitled APPARATUS AND METHOD FOR TRACE STREAM IDENTIFICATION OF A PROCESSOR RESET, invented by Gary L. Swoboda and Bryan Thome, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,214, entitled APPARATUS AND METHOD FOR TRACE STREAM IDENTIFICATION OF A PROCESSOR DEBUG HALT, invented by Gary L. Swoboda, Bryan Thorne, Lewis Nardini, and Manisha Agarwala, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,327, entitled APPARATUS AND METHOD FOR TRACE STREAM IDENTIFICATION OF A PIPELINE FLATTENER PRIMARY CODE FLUSH FOLLOWING INITIATION OF AN INTERRUPT SERVICE ROUTINE; invented by Gary L. Swoboda and Bryan Thome, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,647, entitled APPARATUS AND METHOD FOR TRACE STREAM IDENTIFICATION OF A PIPELINE FLATTENER SECONDARY CODE FLUSH FOLLOWING A RETURN TO PRIMARY CODE EXECUTION, invented by Gary L. Swoboda and Bryan Thome, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,401, entitled APPARATUS AND METHOD IDENTIFICATION OF A PRIMARY CODE START SYNC POINT FOLLOWING A RETURN TO PRIMARY CODE EXECUTION, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U. S. patent application Ser. No. 10/729,326, entitled APPARATUS AND METHOD FOR IDENTIFICATION OF A NEW SECONDARY CODE START POINT FOLLOWING A RETURN FROM A SECONDARY CODE EXECUTION, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,190, entitled APPARATUS AND METHOD FOR TRACE STREAM IDENTIFICATION OF A PAUSE POINT IN A CODE EXECTION SEQUENCE, invented by Gary L. Swoboda, filed on even date herewith, and assigned to the assignee of the present application; U.S. patent application Ser. No. 10/729,196, entitled APPARATUS AND METHOD FOR COMPRESSION OF A TIMING TRACE STREAM, invented by Gary L. Swoboda and Bryan Thome, filed on even date herewith, and assigned to the assignee of the present application; and U.S. patent application Ser. No. 10/729,191, entitled APPARATUS AND METHOD FOR OP CODE EXTENSION IN PACKET GROUPS TRANSMITTED IN TRACE STREAMS, invented by Gary L. Swoboda and Bryan Thome, filed on even date herewith, and assigned to the assignee of the present application are related applications.


BACKGROUND OF THE INVENTION 
1. Field of the Invention
This invention relates generally to the testing of digital signal processing units and, more particularly, to the signals that are transmitted from a target processor to a host processing to permit analysis of the target processing unit operation. Certain events in the target processor must be communicated to the host processing unit along with contextual information. In this manner, the test and debug data can be analyzed and problems in the operation of the target processor identified.
2. Description of the Related Art
As microprocessors and digital signal processors have become increasingly complex, advanced techniques have been developed to test these devices. Dedicated apparatus is available to implement the advanced techniques. Referring to FIG. 1A, a general configuration for the test and debug of a target processor 12 is shown. The test and debug procedures operate under control of a host processing unit 10. The host processing unit 10 applies control signals to the emulation unit 11 and receives (test) data signals from the emulation unit 11 by cable connector 14. The emulation unit 11 applies control signals to and receives (test) signals from the target processing unit 12 by connector cable 15. The emulation unit 11 can be thought of as an interface unit between the host processing unit 10 and the target processor 12. The emulation unit 11 processes the control signals from the host processor unit 10 and applies these signals to the target processor 12 in such a manner that the target processor will respond with the appropriate test signals. The test signals from the target processor 12 can be a variety types. Two of the most popular test signal types are the JTAG (Joint Test Action Group) signals and trace signals. The JTAG protocol provides a standardized test procedure in wide use in which the status of selected components is determined in response to control signals from the host processing unit. Trace signals are signals from a multiplicity of selected locations in the target processor 12 during defined period of operation. While the width of the bus 15 interfacing to the host processing unit 10 generally has a standardized dimension, the bus between the emulation unit 11 and the target processor 12 can be increased to accommodate an increasing amount of data needed to verify the operation of the target processing unit 12. Part of the interface function between the host processing unit 10 and the target processor 12 is to store the test signals until the signals can be transmitted to the host processing unit 10.
Referring to FIG. 1B, the operation of the trigger generation unit 19 is shown. The trigger unit provides the main component by which the operation/state of the target processor can be altered. At least one event signal is applied to the trigger generation unit 19. Based on the identity of the event signal(s) applied to the trigger generation unit 19, a trigger signal is selected. Certain events and combination of events, referred to as an event front, generate a selected trigger signal that results in certain activity in the target processor, e.g., as a debug halt. Combinations of different events generating trigger signals are referred to as jobs. Multiple jobs can have the same trigger signal or combination of trigger signals. In the test and debug of the target processor, the trigger signals can provide impetus for changing state in the target processor or for performing a specified activity. The event front defines the reason for the generation of trigger signal. This information is important in understanding the operation of the target processor because, as pointed out above, several combinations of events can result in the generation of the same trigger signal. In order to analyze the operation of the target processing unit, the portion of the code resulting in the trigger signal must be identified. However, the events in the host processor leading to the generation of event signals can be complicated. Specifically, the characteristics of an instruction at a program counter address can determine whether a trigger signal should be generated. A trigger signal can be an indication of when an address is within a range of addresses, outside of a range of addresses, some combination of address characteristics, and/or the address is aligned with a reference address. In this instance, the address can be the program address of an instruction or a memory address directly or indirectly referenced by a program instruction.
As will be seen, event signals can come from several sources. And these event signals provide a plurality of related signals that should be included in a trace stream in order to reconstruct the target processor activity. In addition, event signals and other signals that must be communicated to the host processing unit may occur simultaneously. The communication of the simultaneous occurrence of conditions in the target processor should be performed with a minimum of additional equipment and with a minimum impact on the band width of the trace streams.
A need has been felt for apparatus and an associated method having the feature that a plurality of simultaneous target processor events can be communicated to the host processing unit. It is another feature of the apparatus and associated method to communicate occurrence of the simultaneous events to the host processing unit using trace stream sync marker procedures. It is a still further feature of the apparatus and associated method to communicate to the host processing unit the occurrence of a plurality of simultaneous events in the target processor using a minimum of information. It is yet another object of the apparatus and associated method to communicate the occurrence of a plurality of simultaneous events with a minimum of new apparatus.
SUMMARY OF THE INVENTION 
The aforementioned and other features are accomplished, according to the present invention, by providing the target processor with at least two trace streams. One of the trace streams is a timing trace stream. The second trace stream, when an event is identified, is provided with a sync marker. The sync marker includes at least one portion identifying the event resulting in the sync marker, a portion relating the event to the timing trace stream, and a portion identifying the point in the program execution when the event is identified. The trace streams are implemented with signal packets. When more than one simultaneous event is to be communicated to the host processing unit, an additional packet in the storage unit in which the sync marker is assembled is activated. Each of the locations in the additional packet can be associated with one event. During the assembly of the sync marker, one event is identified in the normal fashion, i.e., the header of a packet sync marker group. The remaining event or events have a logic signal stored in the associated location in the additional packet. After the assembly, the expanded sync marker is transferred to the host processing unit. In the preferred embodiment, the second trace stream is a program counter trace stream. The point in the program execution where the events are identified is determined by the program counter address included in the sync marker. The time of the occurrence of the events in the target processor is determined by trace synchronization markers and by a position of a clock cycle in a timing packet.
Other features and advantages of present invention will be more clearly understood upon reading of the following description and the accompanying drawings and the claims.



BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1A is a general block diagram of a system configuration for test and debug of a target processor, while FIG. 1B illustrates a trigger unit in the target processor.
FIG. 2 is a block diagram of selected components in the target processor used the testing of the central processing unit of the target processor according to the present invention.
FIG. 3 is a block diagram of selected components of the illustrating the relationship between the components transmitting trace streams in the target processor.
FIG. 4A illustrates format by which the timing packets are assembled according to the present invention, while FIG. 4B illustrates the inclusion of a periodic sync marker in the timing trace stream.
FIG. 5 illustrates the parameters for sync markers in the program counter stream packets according to the present invention.
FIG. 6A illustrates the sync markers in the program counter trace stream when a periodic sync ID signal is generated, while FIG. 6B illustrates the reconstruction of the target processor operation from the trace streams according to the present invention.
FIG. 7 is a block diagram illustrating the apparatus used in reconstructing the processor operation from the trace streams according to the present invention.
FIG. 8A is block diagram of the program counter sync marker generator unit; FIG. 8B illustrates the additional apparatus needed to form a sync marker for a plurality of events, FIG. 8C illustrates the multiple-event sync marker in the trace stream, and FIG. 8D illustrates the reconstruction of the trace streams by the host processing unit.



DESCRIPTION OF THE PREFERRED EMBODIMENT 
1. Detailed Description of the Figures
FIG. 1A and FIG. 1B have been described with respect to the related art.
Referring to FIG. 2, a block diagram of selected components of a target processor 20, according to the present invention, is shown. The target processor includes at least one central processing unit 200 and a memory unit 208. The central processing unit 200 and the memory unit 208 are the components being tested. The trace system for testing the central processing unit 200 and the memory unit 202 includes three packet generating units, a data packet generation unit 201, a program counter packet generation unit 202 and a timing packet generation unit 203. The data packet generation unit 201 receives VALID signals, READ/WRITE signals and DATA signals from the central processing unit 200. After placing the signals in packets, the packets are applied to the scheduler/multiplexer unit 204 and forwarded to the test and debug port 205 for transfer to the emulation unit 11. The program counter packet generation unit 202 receives PROGRAM COUNTER signals, VALID signals, BRANCH signals, and BRANCH TYPE signals from the central processing unit 200 and, after forming these signal into packets, applies the resulting program counter packets to the scheduler/multiplexer 204 for transfer to the test and debug port 205. The timing packet generation unit 203 receives ADVANCE signals, VALID signals and CLOCK signals from the central processing unit 200 and, after forming these signal into packets, applies the resulting packets to the scheduler/multiplexer unit 204 and the scheduler/multiplexer 204 applies the packets to the test and debug port 205. Trigger unit 209 receives EVENT signals from the central processing unit 200 and signals that are applied to the data trace generation unit 201, the program counter trace generation unit 202, and the timing trace generation unit 203. The trigger unit 209 applies TRIGGER and CONTROL signals to the central processing unit 200 and applies CONTROL (i.e., STOP and START) signals to the data trace generation unit 201, the program counter generation unit 202, and the timing trace generation unit 203. The sync ID generation unit 207 applies signals to the data trace generation unit 201, the program counter trace generation unit 202 and the timing trace generation unit 203. While the test and debug apparatus components are shown as being separate from the central processing unit 201, it will be clear that an implementation these components can be integrated with the components of the central processing unit 201.
Referring to FIG. 3, the relationship between selected components in the target processor 20 is illustrated. The data trace generation unit 201 includes a packet assembly unit 2011 and a FIFO (first in/first out) storage unit 2012, the program counter trace generation unit 202 includes a packet assembly unit 2021 and a FIFO storage unit 2022, and the timing trace generation unit 203 includes a packet generation unit 2031 and a FIFO storage unit 2032. As the signals are applied to the packet generators 201, 202, and 203, the signals are assembled into packets of information. The packets in the preferred embodiment are 10 bits in width. Packets are assembled in the packet assembly units in response to input signals and transferred to the associated FIFO unit. The scheduler/multiplexer 204 generates a signal to a selected trace generation unit and the contents of the associated FIFO storage unit are transferred to the scheduler/multiplexer 204 for transfer to the emulation unit. Also illustrated in FIG. 3 is the sync ID generation unit 207. The sync ID generation unit 207 applies an SYNC ID signal to the packet assembly unit of each trace generation unit. The periodic signal, a counter signal in the preferred embodiment, is included in a current packet and transferred to the associated FIFO unit. The packet resulting from the SYNC ID signal in each trace is transferred to the emulation unit and then to the host processing unit. In the host processing unit, the same sync marker ID in each trace stream indicates that the point at which the trace streams are synchronized. In addition, the packet assembly unit 2031 of the timing trace generation unit 203 applies and INDEX signal to the packet assembly unit 2021 of the program counter trace generation unit 202. The function of the INDEX signal will be described below.
Referring to FIG. 4A, the assembly of timing packets is illustrated. The signals applied to the timing trace generation unit 203 are the CLOCK signals and the ADVANCE signals. The CLOCK signals are system clock signals to which the operation of the central processing unit 200 is synchronized. The ADVANCE signals indicate an activity such as a pipeline advance or program counter advance (( )) or a pipeline non-advance or program counter non-advance (1). An ADVANCE or NON-ADVANCE signal occurs each clock cycle. The timing packet is assembled so that the logic signal indicating ADVANCE or NON-ADVANCE is transmitted at the position of the concurrent CLOCK signal. These combined CLOCK/ADVANCE signals are divided into groups of 8 signals, assembled with two control bits in the packet assembly unit 2031, and transferred to the FIFO storage unit 2032.
Referring to FIG. 4B, the trace stream generated by the timing trace generation unit 203 is illustrated. The first (in time) trace packet is generated as before. During the assembly of the second trace packet, a SYNC ID signal is generated during the third clock cycle. In response, the timing packet assembly unit 2031 assembles a packet in response to the SYNC ID signal that includes the sync ID number. The next timing packet is only partially assembled at the time of the SYNC ID signal. In fact, the SYNC ID signal occurs during the third clock cycle of the formation of this timing packet. The timing packet assembly unit 2031 generates a TIMING INDEX 3 signal (for the third packet clock cycle at which the SYNC ID signal occurs) and transmits this TIMING INDEX 3 signal to the program counter packet assembly unit 2031.
Referring to FIG. 5, the parameters of a sync marker in the program counter trace stream, according to the present invention is shown. The program counter stream sync markers each have a plurality of packets associated therewith. The packets of each sync marker can transmit a plurality of parameters. A SYNC POINT TYPE parameter defines the event described by the contents of the accompanying packets. A program counter TYPE FAMILY parameter provides a context for the SYNC POINT TYPE parameter and is described by the first two most significant bits of a second header packet. A BRANCH INDEX parameter in all but the final SYNC POINT points to a bit within the next relative branch packet following the SYNC POINT. When the program counter trace stream is disabled, this index points a bit in the previous relative branch packet when the BRANCH INDEX parameter is not a logic “0”. In this situation, the branch register will not be complete and will be considered as flushed. When the BRANCH INDEX is a logic “0”, this value point to the least significant value of branch register and is the oldest branch in the packet. A SYNC ID parameter matches the SYNC POINT with the corresponding TIMING and/or DATA SYNC POINT which are tagged with the same SYNC ID parameter. A TIMING INDEX parameter is applied relative to a corresponding TIMING SYNC POINT. For all but LAST POINT SYNC events, the first timing packet after the TIMING PACKET contains timing bits during which the SYNC POINT occurred. When the timing stream is disabled, the TIMING INDEX points to a bit in the timing packet just previous to the TIMING SYNC POINT packet when the TIMING INDEX value is nor zero. In this situation, the timing packet is considered as flushed. A TYPE DATA parameter is defined by each SYNC TYPE. An ABSOLUTE PC VALUE is the program counter address at which the program counter trace stream and the timing information are aligned. An OFFSET COUNT parameter is the program counter offset counter at which the program counter and the timing information are aligned.
Referring to FIG. 6A, a program counter trace stream for a hypothetical program execution is illustrated. In this program example, the execution proceeds without interruption from external events. The program counter trace stream will consist of a first sync point marker 601, a plurality of periodic sync point ID markers 602, and last sync point marker 603 designating the end of the test procedure. The principal parameters of each of the packets are a sync point type, a sync point ID, a timing index, and an absolute PC value. The first and last sync points identify the beginning and the end of the trace stream. The sync ID parameter is the value from the value from the most recent sync point ID generator unit. In the preferred embodiment, this value in a 3-bit logic sequence. The timing index identifies the status of the clock signals in a packet, i.e., the position in the 8 position timing packet when the event producing the sync signal occurs. And the absolute address of the program counter at the time that the event causing the sync packet is provided. Based on this information, the events in the target processor can be reconstructed by the host processor.
Referring to FIG. 6B, the reconstruction of the program execution from the timing and program counter trace streams is illustrated. The timing trace stream consists of packets of 8 logic “0”s and logic “1”s. The logic “0”s indicate that either the program counter or the pipeline is advanced, while the logic “1”s indicate the either the program counter or the pipeline is stalled during that clock cycle. Because each program counter trace packet has an absolute address parameter, a sync ID, and the timing index in addition to the packet identifying parameter, the program counter addresses can be identified with a particular clock cycle. Similarly, the periodic sync points can be specifically identified with a clock cycle in the timing trace stream. In this illustration, the timing trace stream and the sync ID generating unit are in operation when the program counter trace stream is initiated. The periodic sync point is illustrative of the plurality of periodic sync points that would typically be available between the first and the last trace point, the periodic sync points permitting the synchronization of the three trace streams for a processing unit.
Referring to FIG. 7A, the general technique for reconstruction of the trace streams is illustrated. The trace streams originate in the target processor 12 as the target processor 12 is executing a program 1201. The trace signals are applied to the host processing unit 10. The host processing unit 10 also includes the same program 1201. Therefore, in the illustrative example of FIG. 6 wherein the program execution proceeds without interruptions or changes, only the first and the final absolute addresses of the program counter are needed. Using the advance/non-advance signals of the timing trace stream, the host processing unit can reconstruct the program as a function of clock cycle. Therefore, without the sync ID packets, only the first and last sync markers are needed for the trace stream. This technique results in reduced information transfer. FIG. 6 includes the presence of periodic sync ID cycles, of which only one is shown. The periodic sync ID packets are important for synchronizing the plurality of trace streams, for selection of a particular portion of the program to analyze, and for restarting a program execution analysis for a situation wherein at least a portion of the data in the trace data stream is lost. The host processor can discard the (incomplete) trace data information between two sync ID packets and proceed with the analysis of the program outside of the sync timing packets defining the lost data.
As indicated in FIG. 6A, the program counter trace stream includes the absolute address of the program counter for an instruction. Referring to FIG. 7B, each processor includes a processor pipeline 71. When the instruction leaves the processor pipeline, the instruction is entered in the pipeline flattener 73. At the same time, an access of memory unit 72 is performed. The results of the memory access of memory unit 72, which may take several clock cycles, is then merged the associated instruction in the pipeline flattener 73 and withdrawn from the pipeline flattener 73 for appropriate distribution. The pipeline flattener 73 provides a technique for maintaining the order of instructions while providing for the delay of a memory access. In the preferred embodiment, the absolute address used in the program counter trace stream is the derived from the instruction of leaving the pipeline flattener 71. As a practical matter, the absolute address is delayed. It is not necessary to include a pipeline flattener 73 in the target processor. The instructions can have appropriate labels associated therewith to eliminate the need for the pipeline flattener 73.
Referring to FIG. 8A, the major components of the program counter packet generation unit 202 illustrating the generation of the program counter trace stream is shown. The program counter packet generation unit 202 includes a decoder unit 2023, storage unit 2021, a FIFO unit 2022, and a gate unit 2024. PERIODIC SYNC ID signals, TIMING INDEX signals, and ABSOLUTE ADDRESS signals are applied to gate unit 2024. When the PERIODIC SYNC ID signals are incremented, the decoder unit 2023, in response to the PERIODIC SYNC ID signal, stores a periodic sync ID header signal group in a predetermined location 2021A of the header portion of the storage unit 2021. The PERIODIC SYNC signal causes the gate 2024 to transmit the PERIODIC SYNC ID signals, the TIMING INDEX signals and the ABSOLUTE ADDRESS signals. These transmitted signals are stored in the storage unit 2021 in information packet locations assigned to these parameters. When all of the portions of the periodic sync marker have been assembled in the storage unit 2021, then the component packets of the periodic sync marker are transferred to the FIFO unit 2022 for eventual transmission to the scheduler/multiplexer unit. Similarly, when another event signal is generated and applied to the decoder unit 2023, the reset header identifying the event signal is stored in position 2021A in the header portion of the storage unit 2021. The event signal applied to decoder unit 2023 results in a control signal being applied to the gate 2024. As a result of the control signal, the SYNC ID signals, the TIMING INDEX signals, and the ABSOLUTE ADDRESS signals are stored in the appropriate locations in storage unit 2021. When the event signal sync marker has been assembled, i.e., in packets, the sync marker is transferred to the FIFO unit 2022.
Referring to FIG. 8B, the additional apparatus needed to accommodate a multiple-event sync signal is shown. As before, one event is identified by related signals stored in the 2021A locations of the header packets (i.e., storage locations). Multiple-event gate 2027 has applied thereto any remaining event signal. When more than one event signal is applied to the decoder unit 2023, a control signal is applied to the multiple-event gate 2027 and the event signals are applied to locations in the storage locations (packet) 2012B. Each event signal has a specified location in packet 2012B. When an event signal is active, a logic signal is stored in the associated location in packet 2021B. In addition, in response to the control signal, the multiple-event gate applies an op code to locations in the packet 2021B. This op code identifies the packet as being a continuation of the sync marker being assembled in the storage unit 2021. When the sync marker is transferred to the FIFO unit 2022, the additional packet 2021B is transmitted therewith.
Referring to FIG. 8C, examples of the sync markers in the program counter trace stream are shown. The start of the test procedure is shown in first point sync marker 801. Thereafter, periodic sync ID markers 805 can be generated.
Other event markers can also be generated. The identification of multiple simultaneous events results in the generation of multiple-event sync marker 810.
Referring to FIG. 8D, the reconstruction of the program counter trace stream from the sync markers is shown. The first sync point marker indicates the beginning of test procedure with a program counter address of PC. The program continues to execute unit with the program counter addresses being related to a particular processor clock cycle. In the clock cycle following the program counter address PC+3, a periodic sync ID signal is generated. At program counter address PC+5, the multiple-event sync marker is generated.
2. Operation of the Preferred Embodiment
The present invention relies on the ability to of the host processing unit to relate the timing trace stream and the program counter trace stream. This relationship is provided by having periodic sync ID information transmitted in each trace stream. In addition, the timing packets are grouped in packets of eight signals identifying whether the program counter or the pipeline advanced or did not advance. The sync markers in the program counter stream include both the periodic sync ID information and an index indicating the position in the current eight-position timing packet when the event occurred. Thus, the clock cycle of the event can be specified. In addition, the address of the program counter is provided in the program counter sync markers so that the event can be related to the execution of the program. As a result, when a multiple-event sync marker is generated, the location of the events relative to the target processor clock and to the program execution is established and program execution of the target processor can be reconstructed. In the preferred embodiment, data (memory access) information is also transferred from the target processor to the host processing unit in a trace data stream. It is therefore possible to reconstruct the entire operation of the target processor from the transmitted trace streams.
The sync marker trace steams illustrated above relate to an idealized operation of the target processor in order to emphasize the features of the present invention. Numerous other sync events (e.g. branch events) will typically be entered in the program counter trace stream generation unit and included in the program counter trace stream.
In the foregoing discussion, the sync markers can have additional information embedded therein depending on the implementation of the apparatus generating and interpreting the trace streams. This information will be related to the parameters shown in FIG. 5. It will also be clear that a data trace stream, as shown in FIG. 2 will typically be present. The periodic sync IDs as well as the timing indexes will also be included in the data trace stream. In addition, the program counter absolute address parameter can be replaced by the program counter off-set register in certain situations.
While the invention has been described with respect to the embodiments set forth above, the invention is not necessarily limited to these embodiments. Accordingly, other embodiments, variations, and improvements not described herein are not necessarily excluded from the scope of the invention, the scope of the invention being defined by the following claims.

## Claims

1. For the testing of the operation of processing unit, a system for identifying the occurrence of a plurality of events in a processor unit, the system comprising:
timing trace apparatus responsive to signals from the processor unit, the timing trace apparatus generating a timing trace stream;
program counter trace apparatus responsive to signals from the processing unit, the program counter trace apparatus generating a program counter trace stream; and
synchronization apparatus applying periodic signals to the timing trace apparatus and to the program counter trace apparatus, the periodic signals;
wherein the program counter trace apparatus is responsive to plurality of simultaneous event signals, the program counter trace apparatus generating multiple-event sync marker signal group identifying the occurrence of the plurality of simultaneous events and relating the event signals to the timing trace stream and the program execution.

2. The system as recited in claim 1 wherein the marker signal group includes a program counter address, a timing index and a periodic sync ID.

3. The system as recited in claim 1 further comprising:
data trace apparatus responsive to signals from the processing unit, the data trace apparatus generating a data trace stream, wherein the periodic sync ID signals are applied to the data trace apparatus provide periodic sync markers in the data trace stream; and
a host processing unit, the host processing unit responsive to the timing trace stream, the program counter trace stream and the data trace stream, the host processing unit reconstructing the processing activity of the processing unit from the trace streams.

4. The method for communicating an occurrence of a reset signal from a target processor unit to a host processing unit, the method comprising:
generating a timing trace stream, a program counter trace stream, and data trace stream, and
in the program counter trace stream, including a marker signal group indicating a simultaneous occurrence of a plurality of event signals and relating the occurrence to the data trace stream, to the timing trace stream, and to the program execution.

5. The method as recited in claim 4 further including:
in the marker signal group, including a periodic sync ID, a timing index and a program counter address.

6. In a processing unit test environment wherein a target processor transmits a plurality of trace streams to a host processing unit, a marker signal group included in a trace signal stream, the marker signal group comprising:
indicia of the simultaneous occurrence of a plurality of event signals;
indicia of the relationship of the occurrence of a reset signal to the target processor clock; and
indicia of the relationship of the occurrence of the event signals to the target processor program execution.

7. In a target processing unit generating trace test signals for transfer to a host processing unit, program counter trace generation apparatus comprising:
a storage unit;
a decoder unit responsive to a reset signal for storing a signal group identifying a first event signal in the storage unit in a first location in the storage unit, the decoder unit generating a control signal, the decoder unit generating a second control signal when multiple simultaneous events are identified;
a gate unit responsive to the control signal, the gate unit transmitting processor signals applied thereto to the storage unit for storage at defined locations, the signals stored in the storage unit forming a portion of a multiple-event sync marker;
a multiple-event gate unit responsive to the second control signal for storing indicia of additional event signals in the storage unit; and
a FIFO unit coupled to the storage unit, the FIFO unit receiving the multiple-event sync marker when the multiple-event sync marker has been assembled, the FIFO unit transferring the multiple-event sync marker to the host processing unit.

8. The program counter trace apparatus as recited in claim 7 wherein the signals applied to the gate unit include a program counter address, a periodic sync ID, and a timing index.

9. The program counter trace apparatus as recited in claim 8 wherein the multiple-event sync marker signal includes a plurality of packets.

10. The program counter trace apparatus as recited in claim 7 wherein the sync markers in the FIFO unit are transferred from the unit in response to third control signals.