# Patent

## Title
Method for scheduling a network packet processor

## Abstract

A method is provided for scheduling a network packet processor. A textual language specification is input of the processing of network packets by the network packet processor. The textual language specification includes memory read actions and modification actions. Each memory read action reads a stored value from a memory of the network packet processor. Each modification action modifies a field of the network packets. An availability is determined for each field read from the network packets for the memory read and modification actions. An availability is determined for each stored value read from the memory for the memory read actions. A look-ahead interval is determined from the availabilities. A respective storage class is determined for the fields for the memory read and modification actions. The respective storage class is one of a bus, a register, and a register with bypass.

## Background
FIELD OF THE INVENTION
The present invention generally relates to processors of network packets, and more particularly to generation of a network packet processor.
BACKGROUND
A network packet processor may input a stream of network packets, manipulate the contents of the network packets, and output another stream of modified network packets. The manipulations may implement a protocol for processing network packets. For example, the network packet processor may implement a protocol layer of a communication protocol, and for a high-level packet received from a higher protocol layer and delivered to a lower protocol layer for eventual transmission on the communication media, the manipulations may encapsulate the high-level packet within a low-level packet of the lower protocol layer.
A protocol designer may develop a specification of the processing of network packets by a network packet processor. A hardware designer, such as an integrated circuit designer, may create a hardware implementation of a network packet processor that complies with the requirements specified by the protocol designer. Thus, development of a network packet processor implemented in hardware may require the specialized knowledge and skills of at least two separate fields of expertise. Because multiple fields of expertise may be required during development of a hardware implementation of a network packet processor, development of a network packet processor may be time consuming and expense.
Rapid development of the protocol or implementation of a network packet processor may improve the timeliness and/or quality of the network packet processor. For example, if a hardware implementation can be generated quickly given a specification of the processing of network packets, deficiencies discovered in an initial implementation may be addressed by modifying the specification and generating an improved implementation. Additional iterations of improvement may be possible if the hardware implementation can be generated quickly from a protocol specification.
The present invention may address one or more of the above issues.
SUMMARY
Various embodiments of the invention provide a method for scheduling a network packet processor. A textual language specification is input of the processing of a type of network packets by the network packet processor. The textual language specification includes one or more memory read actions and one or more modification actions. Each memory read action reads a stored value from a memory of the network packet processor. Each modification action modifies a field of the type of network packets. A respective availability is determined for each field read from the network packets for the memory read and modification actions. A respective availability is determined for each stored value read from the memory for the memory read actions. The availabilities are relative to a beginning of the type of network packets. A look-ahead interval is determined in response to the availabilities of the fields for the modification actions and the stored values for the memory read actions. A respective storage class is determined for the fields for the memory read and modification actions. The respective storage class is one of a bus, a register, and a register with bypass.



BRIEF DESCRIPTION OF THE DRAWINGS
Various aspects and advantages of the invention will become apparent upon review of the following detailed description and upon reference to the drawings in which:
FIG. 1 is a block diagram of a system for generating a hardware description language specification of a network packet processor in accordance with various embodiments of the invention;
FIG. 2 is a listing of an example textual language specification of a network packet processor in accordance with various embodiments of the invention;
FIG. 3 is a data flow diagram of a process of generating a hardware description language specification of a network packet processor in accordance with various embodiments of the invention;
FIG. 4 is a block diagram of a network packet processor that is generated in accordance with various embodiments of the invention;
FIG. 5 is a flow diagram of a process for generating a pipeline for processing network packets in accordance with various embodiments of the invention;
FIG. 6 is a flow diagram of a process for scheduling a network packet processor in accordance with various embodiments of the invention;
FIG. 7 is a diagram illustrating availability of the fields of a network packet in accordance with various embodiments of the invention;
FIG. 8 is a diagram of a dependency graph for memory read actions of a network packet processor in accordance with various embodiments of the invention;
FIG. 9 is a diagram of a dependency graph for modification actions of a network packet processor in accordance with various embodiments of the invention; and
FIGS. 10A, 10B, and 10C are block diagrams of storage classes for fields read from a network packet in accordance with one or more embodiments of the invention.



DETAILED DESCRIPTION
Various embodiments of the invention permit a network packet processor to be implemented from a specification of the required processing of network packets by the network packet processor. The implementation of the network packet processor may be a hardware implementation in a programmable logic device (PLD) that may be quickly generated from the specification of the processing protocol of the network packet processor. The generated hardware implementation may have low latency and may efficiently utilize the resources of the PLD.
FIG. 1 is a block diagram of a system for generating a hardware description language (HDL) specification of a network packet processor in accordance with various embodiments of the invention. A processor 102 reads and executes instructions from a program storage medium 104, and the execution of the instructions causes processor 102 to generate the HDL specification of the network packet processor. Software modules 106 and 108 may include the instructions of the program storage medium 104.
Execution of the instructions of software module 106 may cause processor 102 to input a specification of the processing to be performed by the network packet processor. In one embodiment, the network packet processor may receive network packets and transmit a modification of the received network packets. The specification of the processing by the network packet processor may be a protocol specification of the modifications to be performed by the network packet processor. For example, the network packet processor may implement a protocol layer of a communication protocol, and for a high-level packet received from a higher protocol layer and delivered to a lower protocol layer for eventual transmission on the communication media, the specification may describe the encapsulation of the high-level packet within a low-level packet of the lower protocol layer. The encapsulation specified by the protocol specification may include insertion of a header with a particular format before the beginning of the high-level packet. The header may be generated from information in the incoming high-level packet and from information that is stored within the network packet processor.
Execution of the instructions of software module 106 may cause processor 102 to input the specification from the user interface 110. In one embodiment, the user interface 110 may permit directly inputting a textual language specification of the processing expected from the network packet processor. In another embodiment, the textual language specification may be input from a data file stored in program storage medium 104 or another storage medium of the system.
Execution of the instructions of software module 108 may cause processor 102 to generate an HDL specification of the network packet processor from the textual language specification input by processor 102 during execution of the instructions of software module 106. The network packet processor generated using software module 108 may implement the manipulations of the textual language specification.
Execution of the instructions of the optional software module 112 may cause processor 102 to translate the specification of the network packet processor into a simulator in a general purpose programming language and to simulate the network packet processor using the simulator.
FIG. 2 is a listing of an example textual language specification of a network packet processor in accordance with various embodiments of the invention. Various embodiments of the invention may translate the example textual language specification into a network packet processor that processes network packets as specified. The specification includes a declaration 202 of the name the network packet processor, a declaration 204 of the ports of the network packet processor, a declaration 206 of formats of types of network packets and other data structures, a declaration 207 of a global variable, and a specification 208 of a handler procedure for processing the network packets by the network packet processor.
As specified in ports declaration 204, the network packet processor has an input port with identifier “packetin” for receiving network packets, an output port with identifier “packetout” for transmitting network packets, and a memory port with identifier “memoryreq” for accessing an external memory. As specified in the handler specification 208, the network packets received at the input port are modified and the modified network packets are transmitted from the output port. Certain of the received network packets are modified using data that is read from an external memory using the memory port. It will be appreciated that a network packet may also be modified using state data that is stored within the network packet processor.
The handler specification 208 specifies processing of network packets that have type “IPpacket” and are received at the input port “packetin.” The handler specification 208 includes a declaration 210 of a local variable and specifications of five actions, including set action 212, set action 213, memory read action 214, insert action 216, and forwarding action 218. For each network packet of type “Ippacket” that is received at the input port “packetin,” set action 212 decrements the “TTL” field of the network packet. Set action 213 sets the value of the “checksum” field to a value of the global variable of declaration 207. Memory read action 214 reads a memory at the address given by the “id” field of the network packet. The insert action 216 includes a guard condition within the square brackets that enables the insert action 216 when the “version” field of the network packet has a value of 4, and otherwise the insert action 216 is disabled. If the insert action 216 is enabled by the guard condition, the insert action 216 inserts data from the memory read action 214 after the “destination” field of the network packet. Forwarding action 218 transmits the modified network packet at the output port “packetout.”
The value of the global variable of declaration 207 could be updated by a handler procedure during the processing of one network packet, and the updated value could be used during the processing of another network packet by the handler procedure. Thus, the global variable of declaration 207 may provide state data that is preserved between network packets. In contrast, the local variable of declaration 210 may be temporary data that should be reinitialized for each network packet that is processed.
The textual language for specifying the processing of a network packet handler may closely correspond with the techniques that a designer uses to specify a communication protocol. A designer of communication protocol may develop the textual language specification without having the specialized knowledge required to develop an integrated circuit, and various embodiments of the invention may translate the textual language specification of a communication protocol into an efficient implementation of the communication protocol in a network packet processor. Thus, various embodiments of the invention permit a designer of a communication protocol to develop an integrated circuit for efficiently implementing the communication protocol even though the designer does not have the skills for designing an integrated circuit.
FIG. 3 is a data flow diagram of a process of generating a hardware description language (HDL) specification 302 of a network packet processor in accordance with various embodiments of the invention. The HDL specification 302 may be generated from a textual language specification 304 of the processing performed by the network packet processor.
The textual language specification 304 of the network packet processor may include port identifiers 306 and 308, global variables 309, a format 310 or formats for one or more types of network packets and possibly other data structures, and a procedure 312 for each input port and each type of network packet that is expected at the input port of the network packet processor. The port identifiers 306 and 308 may include respective identifiers for the input, output, and any memory ports of the network packet processor. The global variables 309 may provide state data that is preserved between network packets. A format 310 includes the fields 314 and 316 of a type of network packet, and a field 314 or 316 may be declared in the format 310 as having a specified name and a specified size, such as a number of data bits of the field. The fields 314 and 316 may be specified in format 310 in an order corresponding to an order of the network packet manager receiving or transmitting the fields in the type of network packets.
A procedure 312 may include actions 318, 320, and 322 for manipulating network packets of a particular type that are received at a particular input port. Examples for actions 318, 320, and 322 include a set action for setting a value of a field 314 as a function of global variables 309 and/or fields 314 and/or 316, an insert action for data insertion at a field 314 as a function of global variables 309 and/or fields 314 and/or 316, a remove action for data removal at field 314 as a function of global variables 309 and/or fields 314 and/or 316, an update action for updating one of the global variables 309 as a function of the global variables 309 and/or fields 314 and/or 316, a forward action for transmitting modified network packets from an output port of the network packet processor, a memory read action for reading a value from a memory, and a memory write action for writing a value to the memory.
An action 318 may include a guard condition 324 for enabling and disabling the action 318, with the action 318 performed in response to the guard condition 324 being satisfied and the action 318 being bypassed in response to the guard condition 324 not being satisfied. Another action 320 might not include a guard condition and the action 320 may always be performed on each network packet that is processed using procedure 312. Examples for guard condition 324 include a check of a value of a field 314 of a type of the network packets, a comparison between two fields 314 and 316 of a type of the network packets, and a comparison between a field 314 and one of the global variables 309.
At step 326, the specification 304, which specifies the processing performed by the network packet processor, is input. At step 328, the HDL specification 302 of the network packet processor is generated. To generate the HDL specification 302 of the network packet processor, a specification 330 may be input that specifies the characteristics 332 and 334 of the ports having identifiers 306 and 308. Example characteristics include a width for each of the ports and a signaling protocol for each of the ports.
The generated HDL specification 302 may include a look-ahead stage 336, an operation stage 338, an insert/remove stage 340, and an interleave stage 342. The look-ahead stage 336 may synchronize among the fields 314 and 316 that are accessed by the actions 318, 320, and 322 of the procedure 312. The look-ahead stage 336 may make certain of fields 314 and 316 concurrently available for processing according to the actions 318, 320, and 322 of the procedure 312. The operation stage 338 may implement the actions 318, 320, and 322 that are not insert or remove actions. For each set action, the operation stage may set one of fields 314 and 316 according to the set action. The operation stage 338 may evaluate a guard condition 324 for an action 318, and bypass performing the action 318 when the guard condition 324 is not satisfied. The insert/remove stage 340 may perform data insertion and/or data removal at one or more of fields 314 and 316 according to the actions 318, 320, and 322 that are insert or remove actions. The data insertion or data removal may be bypassed for an insert or remove action with a guard condition that is not satisfied. The interleave stage 342 may ensure that the modified network packet follows rules for interleaving network packets.
A sequence of network packets may be received at an input port of the network packet processor, with each network packet including a series of data chunks. The data chunks for the network packets may be serially received in an interleaved manner. For example, network packet A may include data chunks A[0], A[1], and A[2], and network packet B may include data chunks B[0], B[1], and B[2], which are serially received at an input port of the network packet processor in the interleaved order A[0], B[0], A[1], B[1], A[2], B[2]. For a network packet processor with an insert/remove stage 340 that modifies network packet A by removing a portion of data chunk A[1], to output full data chunks the network packet processor may need to fill in modified data chunk A[1] with data from subsequent chunks of network packet A. Similarly, for a network packet processor with an insert/remove stage 340 that modifies network packet B by inserting data into chunk B[1], to output proper data chunks the network packet processor may need to move data from modified data chunk B[1] to subsequent chunks of network packet B.
In one embodiment, a data chunk is the data width of the input and output ports of a network packet processor. The interleaving rules may permit interleaving of network packets between each data transfer across the width of a port of the network packet processor. After a data insertion or data removal with a size that is not a multiple of the data chunk, the interleave stage 342 may pad the modified network packet with enough null data to make a full data chunk at the end of the network packet. It will be appreciated that the interleave stage 342 may be useful for generating complete data chunks across the full width of the input and output ports even though data chunks for different network packets are never interleaved.
In another embodiment, a data chunk is a burst of a fixed or variable number of data transfers across the width of a port of the network packet processor, and interleaving of network packets may occur between the bursts of the data chunks. For a variable number of data transfers, the interleaving rules may specify an upper limit on the number of data transfers within a burst. After a data insertion that increases the size of a network packet beyond the fixed number of data transfers allowed for a burst or beyond the upper limit on a variable number of data transfers for a burst, the interleave stage 342 may divide the modified network packet into multiple bursts to satisfy the interleaving rules.
It will be appreciated that the port characteristics 330 may specify both the width of the ports and the burst lengths for the ports. In addition, port characteristics 330 may specify whether network packets are received in an interleaved manner by the network packet processor.
FIG. 4 is a block diagram of a network packet processor that is generated in accordance with various embodiments of the invention. The network packet processor is a pipeline 400 that includes a look-ahead stage 402, an operation stage 404, an insert/remove stage 406, and an interleave stage 408. Stages 402, 404, 406, and 408 of the pipeline 400 are configured by a textual language specification of the processing by the network packet processor.
The textual language specification may specify one or more actions for modifying the fields of a network packet as a function of the fields of the network packet and global variables corresponding to stored state 428 and 450 within the network packet processor. For example, a set action may modify a field of a network packet as a function of another field of this network packet, and these two fields may be received at different times during a serial reception of the data chunks of the network packet. Each modification of a field may be completed upon receiving the field providing the field is modified as a function of stored state and fields that are already available from the network packet. In contrast, a modification of a field might not be possible upon receiving the field when the field is modified as a function of a field or fields that are later received. The look-ahead stage 402 may effectively advance the availability of each field that is used to modify an earlier-received field, such that the operation stage 404 may perform the modification for each set action upon receiving the data chunk that includes the field that is modified by the set action.
To effectively advance the availability of certain fields, the look-ahead stage 402 may promptly provide these fields from look-ahead queue 410, while the look-ahead stage 402 may provide other fields with delayed availability from delay FIFO 412. Various fields may be concurrently available from the look-ahead queue 410 and the delay FIFO 412. The delay FIFO 412 may have a depth equaling the maximum amount of relative advancement that is needed. If no fields need advanced availability for a particular textual language specification, the look-ahead stage 402 may be omitted from the pipeline 400.
Certain fields of a network packet that need advanced availability may be selected by pre-fetch block 414 and stored in look-ahead queue 410 during reception of the network packet at the input port on line 416. Because these fields are promptly made available to the operation stage 404 from look-ahead queue 410, these fields are effectively advanced relative to fields that are later made available to the operation stage 404 from delay FIFO 412.
The network packet processor may access a memory or memories during the processing of a network packet. For example, an address for a memory read action may be formed from a field of the network packet and a set action may modify the same field of the network packet using the value read from the memory at the address. The set action may include a guard condition that enables modifying the same field with a modification value, and either the guard condition or the modification value of the set action may be dependent on the value read from the memory. If a delay interval is required for reading the memory, the modification of the field might not be immediately possible upon receiving the field. The delay interval may be a latency of the memory and/or a time interval needed to form wide data by reading narrow data multiple times from the memory. The look-ahead stage 402 may also effectively advance the availability of certain fields needed for reading from one or more memories.
For the memory read actions that need advanced availability and that access the memory connected to the memory port on line 420, memory pre-fetch block 418 may capture any fields needed to generate any addresses for these memory read actions. Memory pre-fetch block 418 may also capture the fields needed to generate any guard conditions for these memory read actions.
Similarly, memory pre-fetch block 422 may capture the fields needed to determine any addresses and any guard conditions for the memory read actions that need advanced availability for the memory connected to the memory port on line 424. When advanced availability is needed for a value read from a memory for a memory read action, the amount of advanced availability may contribute to determining the depth of the delay FIFO 412.
The stored state block 428 may include state data for certain of the global variables of the specification of the processing of the network packet processor. Some of the global variables may be used in actions needing advanced availability, and the stored state block 428 of look-ahead stage 402 may store the state data for these global variables, while the stored state block 450 of operation stage 404 may store the state data for the remaining global variables.
Certain fields of a network packet may be referenced by multiple actions of the textual language description. For example, a specific field may be referenced by two set actions, which modify respective fields that are in different data chunks and are consequently received by the pipeline 400 at different times. Thus, certain fields may need to be available at multiple time steps and to eliminate duplicated storage these fields may be stored in a register within shared block 426. Shared block 426 may make these fields and/or certain temporary variables available to one or more of blocks 414, 418, and 422.
The control block 430 may control the sampling of certain fields of a network packet by the blocks 428, 426, 414, 418, and 422 as specified by the certain actions of the textual language specification.
The operation stage 404 may implement the actions of the textual language specification excluding the insert and remove actions. The edit block 432 may perform the set actions on each network packet as the data chunks of the network packet are received from the delay FIFO 412 of the look-ahead stage 402. The edit block 432 may perform the set actions using fields with advanced availability from the look-ahead queue 410 of the look-ahead stage 402 and memory read results from the memory read blocks 434, 436, and 438.
The edit block 432 may determine information that is provided to the memory write blocks 440, 442, and 444, and to the insert/remove block 446. Certain fields and/or temporary variables may be shared between the shared block 448 and the blocks 432, 434, 436, 438, 440, 442, 444, and 446. The edit block 432 may update the values of any temporary variables in the shared block 448.
Because the memory connected to the memory port on line 420 may have a memory read action that produces a read result needing advanced availability, the memory read block 434 may receive certain fields with advanced availability from the look-ahead queue 410. These fields may be used to determine any address or any guard conditions for this memory read action. Any address or guard condition for this memory read action may also be determined from other fields that do not need advanced availability and state data from stored state 450.
The memory read block 434 may implement all of the memory read actions that target the memory connected to the memory port on line 420. Depending upon whether or not the read result needs advanced availability for a memory read action accessing the memory port on line 420, the memory read block 434 may generate an address or guard condition for the memory read action using information from the look-ahead queue 410, or the memory read block 434 may generate an address or guard condition using information from the shared block 448.
The memory read block 438 may implement all of the memory read actions that target the memory connected to the memory port on line 452, and none of these memory read actions may need advanced availability of the read result. Because the memory read block 438 does not need to obtain advanced information from the look-ahead queue 410, no connection is shown between the look-ahead queue 410 and the memory read block 438. For example, the memory connected to the memory port on line 452 may be a FIFO or configuration register that does not require an address and hence advanced availability is not needed for the result read from the memory because the memory may be read at any time.
It will be appreciated that the actual number of memory read blocks 434, 436, and 438 for a particular textual language specification may depend on the number of memories accessed by the memory read actions of the textual language specification. In addition, the connections between the look-ahead queue 410 and the memory read blocks 434, 436, and 438 may depend on whether advanced availability is needed for the memory reach actions of the textual language specification.
For each memory write action of the textual language specification, the edit block 432 may provide the write value along with an optional address and optional guard condition to the write memory blocks 440, 442, and 444. Write memory blocks 440, 442, and 444 may implement the memory write actions that write to the respective memories connected to memory ports on lines 420, 424, and 452.
For each insert action and each remove action of the textual language specification, the insert/remove block 446 may determine the position of the data insertion or data removal and the amount of data to be inserted or removed. The insert/remove block 446 may also determine the value of any guard condition for enabling and disabling the data insertion or data removal. For data insertion, the insert/remove block 446 may determine the insertion data. The insert/remove block 446 may obtain information for determining the position and amount of the data insertion or data removal and the insertion data from the edit block 432 and/or the shared block 448.
The control block 454 may manage the operation of the blocks 432, 434, 436, 438, 440, 442, 444, 446, and 448 of the operation stage 404.
The insert/remove stage 406 implements the insert actions and remove actions of the textual language specification. The insert/remove stage may be omitted from the pipeline 400 for a specific textual language specification that does not include any insert or remove actions. The insertion/removal block 456 performs the data insertion of any insert actions and the data removal of any remove actions according to information received from the insert/remove block 446 of the operation stage 404. The control block 458 controls the operation of the insertion/removal block 456. The insertion/removal block 456 may serially receive potentially modified data chunks of a network packet from the edit block 432 of the operation stage 404. While a data insertion or data removal is not in progress, the data chunks received by the insertion/removal block 456 are the data chunks output by the insertion/removal block 456.
Each insert action and each remove action of a textual language specification may optionally include a guard condition. An action that does not include a guard condition is always enabled, and an action with a guard condition is enabled when the guard condition is determined to have an enabling value.
For a remove action that is enabled, upon receiving the data chunk of the network packet that includes the position of the data removal, the insertion/removal block 456 may output a partial data chunk that includes the portion of the data chunk before the position of the data removal. The insertion/removal block 456 may suspend outputting data chunks until the specified amount of data is removed and the insertion/removal block 456 may subsequently resume outputting data chunks of the network packet. The first data chunk output on resuming output may be a partial data chunk. In one embodiment, multiples of a byte may be inserted and removed and the insertion/removal block 456 outputs a number of bytes in parallel for each word of the burst of a data chunk. Each byte that is output may have a corresponding data valid signal to indicate whether the byte is included in a full or partial data chunk.
For an insert action that is enabled, upon receiving the data chunk of the network packet that includes the position of the data insertion, the insertion/removal block 456 may output a full data chunk and then switch to outputting the insertion data. The final data chunk of the insertion data may be a partial data chunk and the insertion/removal block 456 may subsequently resume outputting full data chunks of the network packet. During the data insertion, the insert/remove stage 406 may stall the operation stage 404 and the look-ahead stage 402 to prevent data loss.
The interleave stage 408 may ensure that the modified network packet follows rules for interleaving network packets. The interleave stage 408 may eliminate the gaps in the valid data from any partial data chunks created by the insert/remove stage 406. The interleave stage 408 may divide a network packet into multiple bursts to satisfy the interleaving rules. The interleave stage 408 may be omitted for a textual language specification that only inserts and removes data that is always a multiple of the size of the data chunk. The interleave stage 408 may be eliminated along with the insert/remove stage 406 for a textual language specification that does not include any insert or remove actions.
The interleave block 460 may generate each data chunk that is output from the pipeline 400 by selecting from either the chunk buffer 462 or the insertion/removal block 456 of the insert/remove stage 406. The chunk buffer 462 may contain a portion of the preceding network packet. The control block 464 may be a state machine that controls the operation of the chunk buffer 462 and the interleave block 460.
FIG. 5 is a flow diagram of a process for generating a pipeline for processing network packets in accordance with various embodiments of the invention. The processing of network packets by the pipeline may be specified in a textual language specification, and this specification may be analyzed to generate a specification of the pipeline in a hardware description language. Synthesis tools may generate a hardware implementation of the pipeline from the generated specification. For example, ISE Foundation available from Xilinx, Inc. may be used to create an implementation of the pipeline in a programmable logic device.
At step 502, the specification of the processing of the pipeline may be analyzed to determine the number of memories accessed by the pipeline. For each memory, a dependency graph may be created for scheduling the memory reads that access the memory. Each memory read may require an optional address and an optional guard condition, and each memory read may provide a result value. The addresses and guard conditions may be calculated from certain fields of a network packet and a node may be added to the dependency graph for each of these fields and for each read result from the memory. These nodes are marked with an availability time relative to a start of the network packet. An availability time for a field may be readily calculated from a position of the field within the network packet and a data width of an input of the pipeline for receiving the network packet. For a read result that is dependent on a set of fields for calculating the address and guard condition, the read result may be marked with an availability time that is the sum of the latency for the memory read and the latest availability time of the fields in the set. It will be appreciated that for a memory read without an address and without a guard condition, such as a read from a configuration memory, the result of the memory read may be marked as available at time zero corresponding to the beginning of the network packet.
The optional address and optional guard condition of each memory read may also be dependent on a local variable that is further dependent on certain fields of a network packet, global variables, or the results of other memory reads. Additional nodes may similarly be added and marked in the dependency graph for these indirect dependencies.
Once each dependency graph is resolved to assign an availability time to each node in the graph, each memory read is scheduled to provide the read result at the availability time of the read result. For a memory having a non-zero read latency, the memory read may be issued in advance to provide the read result at the required time. Because a result from a memory read may be used to determine the address or guard condition of another memory read, perhaps indirectly via a local variable, iteration may be required to completely resolve the dependency graph.
At step 504, a storage class may be determined for each field used to generate the address and guard conditions of the memory reads. For a field with an availability time that matches the issue time of every memory read that uses the field, the storage class may be a wire class indicating a direct connection. For a field with an availability time in advance of the issue time of every memory read that used the field, the storage class may be a register class. Otherwise, the storage class may be a register with a bypass path.
At step 506, a depth of the delay FIFO of the look-ahead stage may be determined. The delay FIFO may receive a stream of network packets from an input of the pipeline and the delay FIFO may output the stream of network packets after a fixed time delay, which is set by the depth of the delay FIFO.
In one embodiment, the depth may be selected to have the delay FIFO output the start of a network packet at a time when the results are available for all of the memory reads. Thus, the depth of the delay FIFO may equal the largest value of the availability times of the read results from the dependency graph or graphs. The delay FIFO may be regarded as effectively advancing the memory read results to ensure availability at time zero when the start of the network packet is output from the delay FIFO.
In another embodiment, a usage time and a difference between the usage time and the availability time is determined for each memory read result and the depth of the delay FIFO may equal the largest difference for the memory read results that have a usage time before the availability time.
At step 508, a dependency graph may be created for scheduling the modifications of a network packet. A network packet may be modified by changing a field of the network packet, inserting data into a network packet, or removing data from a network packet. Various fields of the network packet may be used to determine, for example, a modification value for changing a field of a network packet or a packet-dependent length of data to be inserted or removed at a field of the network packet. Certain fields of the network packet may also be used to determine a guard condition for enabling or disabling a field modification or a data insertion or deletion.
A node may be added to the dependency graph for each of these fields and these nodes may be marked with an availability time of the receiving the field relative to a start of the network packet. Additional nodes may be added for the calculated modifications and these additional nodes may be marked with corresponding availability times. From the dependency graph, the modifications of the network packet may be scheduled at the availability times determined for the guard conditions of the modifications, the modification values, the variable locations of data insertion or removal, the variable lengths of data insertion or removal, and the insertion data values.
The FIFO depth selected at step 506 may provide inadequate advancement of some of the fields used for packet modifications. At step 510, these additional fields needing look-ahead may be identified, and the FIFO depth determined at step 506 may be increased and consequently the storage classes determined at step 504 may be adjusted. At step 512, the storage classes are determined for the fields used for packet modifications.
At step 514, a specification of the look-ahead, operation, insert/remove, and interleave stages may be generated in a hardware description language.
FIG. 6 is a flow diagram of a process for scheduling a network packet processor in accordance with various embodiments of the invention. As fields become available during the receipt of a network packet, the network packet processor may store certain fields in a register for later use in processing the network packet. A storage register might not be needed for processing a field that is used at the same time the field becomes available from the incoming network packet.
At step 602, a textual language specification is input that specifies the processing of a type of network packets. The textual language specification may include a memory read action for reading a value from a memory and/or a modification action for modifying the value of a field or fields of the network packet. At step 604, the availability is determined of the fields used for input parameters of each memory read action and each modification action. The availability of a field may be a time of receipt of the field relative to a time of receipt of the beginning of the network packet. At step 606, the availability is determined of the value read from a memory for each memory read action. The availability of a value read from a memory for a memory read action may be the time that the value becomes available relative to a time of receipt of the beginning of the network packet. The availability of a value read from a memory for a memory read action may be a latency of the memory added onto the latest availability determined at step 604 of the fields that are used for determining the parameters of the memory read action.
For certain specifications of the processing of a type of network packets, the network packet processor may transmit a modification of a network packet while the network packet is still being received. For example, the network packet processor implementing a particular specification may be a pipeline that modifies the network packets as the network packets flow through the pipeline, and the beginning of a modification of a network packet may be transmitted before receiving the end of the network packet because the pipeline has fewer stages than the number of cycles needed to receive the network packet.
For certain other specifications of the processing of a type of network packets, a complete network packet may need to be received and stored in a buffer before a modification of the network packet can be transmitted. For example, a specification may specify that the first field of a network packet is modified with a value that depends on the value of the last field of the network packet. Thus, the value of the last field of the network packet should be received before transmitting the modification of the first field of the network packet. The look-ahead interval may be the extra time delay needed for buffering a network packet because the modification of a field of the network packet is dependent on another field that may be received earlier. The amount of the look-ahead interval is determined at step 608.
In one embodiment, the look-ahead interval may be a maximum of the availabilities determined at steps 604 and 606 for the modification and memory read actions. The values of the fields for parameters of the modification actions may be stored as these fields are received. Similarly, the values read from memory for the memory read actions may be stored as soon as these values become available. As these fields and the memory read values are being stored, the entire received network packet may be sent through a FIFO queue that provides a delay equaling the look-ahead interval. With the look-ahead interval set to the maximum of the availabilities determined at steps 604 and 606, the stored fields and memory read values are all available at or before the beginning of the network packet starts to flow out of the delay FIFO queue. Thus, these stored fields and memory read values can be used to modify any field as the network packet flows out of the delay FIFO queue, regardless of the timing of the usage of the stored field. In effect, the availability of the stored fields and memory read values is advanced by the delay FIFO queue to being available at the beginning of the network packet.
In another embodiment, both the time of availability and the time of usage of the stored fields and memory read values are used to determine the look-ahead interval at step 608. The look-ahead interval may be a maximum of the intervals between the availability and the usage for the stored fields and memory read values. The size of the delay FIFO queue may be reduced or the delay FIFO queue may be eliminated by considering the time of usage of the stored fields and memory read values when determining the look-ahead interval.
At step 610, a storage class is determined for each field that is used for determining a parameter of a memory read action or a modification action. The value of a field may be stored in a register for use at a later time. If every usage of the value of a stored field is later than the availability of the field, then the storage class may be a register. The value of a stored field may also be used as soon as the value becomes available. If every usage of the value of a stored field is at the time the value becomes available, then a wired bus may “store” the value and the storage class may be a bus. If the value of a stored field is used at various times including as soon as the value becomes available and after the value becomes available, then the storage class may be a register with bypass.
FIG. 7 is a diagram illustrating availability of the fields of a type of network packet in accordance with various embodiments of the invention. The availability times 702 of the fields of a type of network packet are shown across the top of FIG. 7. Fields 704, 706, 708, and 710 may become available in parallel at availability time-0 at an input port having a width of 32-bits. Similarly, fields 712 and 714 may become available at time-2, field 716 may become available at time-3, and field 718 may become available at time-4.
FIG. 8 is a diagram of a dependency graph for memory read actions of an example for network packet processor in accordance with various embodiments of the invention. Shown in Example 1 below are memory read actions for processing the type of network packet shown in FIG. 7. FIG. 8 corresponds to the dependency graph for the memory read actions of Example 1. The nodes 802 through 810 are labeled with the name of the field or result and parenthetically marked with the corresponding availability time. The nodes 802 through 810 may be placed in FIG. 8 at a horizontal position according to the availability times that aligns vertically with the corresponding availability times 702 of FIG. 7.










EXAMPLE 1









 
var index : 16;




read index from memoryindex [ source + destination ];




[ version == 4 ]read memoryresult from memorydata [ index ];










The first memory read action of Example 1 includes an address parameter calculated from the sum of fields 716 and 718 of FIG. 7. Node 802 corresponds to the usage of source field 716 and node 804 corresponds to the usage of source field 718 for determining the address parameter of the first memory action of Example 1. Nodes 802 and 804 are parenthetically marked with the availability times of the corresponding fields. Node 806 corresponds to the value of “index” that is read from a memory for this first memory read action. Because the value read from a memory for node 806 is dependent on the address parameter determined from the fields corresponding to nodes 802 and 804, the dependency graph has a directed edge from node 802 to node 806 and a directed edge from node 804 to node 806. Node 806 may be parenthetically marked with the availability time that is a worst case availability of the parameters of the first memory read plus a memory latency for the memory read of one time unit. Thus, the availability time for node 806 may be a unit memory latency added onto the maximum of the availability times of the nodes 802 and 804 having directed edges that terminate at node 806.
The second memory read action of Example 1 above includes parameters that are a guard condition checking the version field 704 of FIG. 7 and an address parameter of the “index” value read from a memory by the first memory read action. Node 808 corresponds to the usage of the version field 704 of FIG. 7 for determining the guard condition of the second memory read action. Node 808 is parenthetically marked with the availability time in the network packet of the version field 704 of FIG. 7. Node 810 corresponds to the result value read from a memory for the second memory read action of Example 1. Because the second memory read has a guard condition dependent on the version field corresponding to node 808, the dependency graph has a directed edge from node 808 to node 810. Because the second memory read has an address parameter dependent on the “index” value read from a memory for the first memory read action, the dependency graph also has directed edge from node 806 to node 810. Node 810 is parenthetically marked with an availability time that is a unit memory latency after the availability of node 806 which has a later availability than node 808.
FIG. 9 is a diagram of a dependency graph for modification actions of an example for a network packet processor in accordance with various embodiments of the invention. Shown in Example 2 below are modification actions for processing the type of network packet shown in FIG. 7. FIG. 9 corresponds to the dependency graph for the modification actions of Example 2. The nodes 820, 822, 826, and 830 are parenthetically marked with an availability time and the nodes 824, 828, and 832 are parenthetically marked with an availability time and a usage time. The nodes 820 through 832 may be placed in FIG. 9 at a horizontal position according to the availability times and aligned vertically with the corresponding availability times 702 of FIG. 7.









EXAMPLE 2







 
var default : 16;
 



[ TOS == 0 ] set default = 0x0000 | set default = 0xFFFF;




set checksum = default;




set TTL = TTL − 1;




insert memoryresult after destination;









Example 2 first calculates a local variable that is used to set the checksum field 714 of FIG. 7. The local variable is set to one value if the TOS field 708 of FIG. 7 has a value of zero and otherwise the local variable is set to another value. Node 820 of FIG. 9 corresponds to the TOS field 708 of FIG. 7, node 822 corresponds to the local variable, and node 824 corresponds to the checksum field 714 of FIG. 7. Because the value of the local variable is dependent in Example 2 on the value of the TOS field 708 of FIG. 7, FIG. 8 has a directed edge from node 820 to node 822. Because the setting of the checksum field 714 of FIG. 7 is dependent in Example 2 on the value of the local variable, FIG. 8 has a directed edge from node 822 to node 824. Node 820 is marked with the availability time of zero from the TOS field 708 of FIG. 7, and node 822 is marked with the same availability time because the local variable can be set as soon as the TOS field becomes available. Because the value is ready for setting the checksum field 714 of FIG. 7 as soon as the local variable is available, Node 824 is marked with the same availability time as node 822. Node 824 is also marked with the usage time of two because this when the checksum field 714 in FIG. 7 becomes available for modification.
Example 2 also includes a set action for decrementing the TTL field 712 in FIG. 7. Node 826 in FIG. 9 corresponds to the reading of the TTL field 712 and node 828 corresponds to the modification of the TTL field 712. Because the value of the TTL field 712 should be read to generate the update value for modifying the TTL field 712, the dependency graph of FIG. 9 has a directed edge from node 826 to node 828. Node 826 is marked with the availability time of the TTL field 712. Because the availability of node 828 is the maximum availability time of the nodes with directed edges terminating at node 828, node 828 is marked with the availability time from node 826. Node 828 is also marked with the usage time when the TTL field 712 becomes available for modification.
Example 2 finally includes an insert action for inserting data, which may be read from a memory as shown in Example 1, after the destination field 718 of FIG. 7. Node 830 of the dependency graph of FIG. 9 may correspond to the data that is inserted and node 832 may correspond to the insertion of the data after the destination field 718. Because data cannot be inserted until the data is available, the dependency graph of FIG. 9 has a directed edge from node 830 to node 832. Node 830 is marked with the availability of the insertion data, and for a specification of the processing of a network packet processor that combines Examples 1 and 2, node 830 may be marked with the availability time from node 810 of FIG. 8. Node 832 is marked with the availability time from node 830 and with the usage time that occurs when the first field following the destination field 718 becomes available for modification.
Node 824 has a usage time for the modification value that is after the availability time of the modification value, and node 828 has a usage time for the modification value that equals the availability time of the modification value. In contrast, node 832 has a usage time for the insertion data that precedes the availability of the insertion data.
A look-ahead interval may be required to effectively advance the availability of the insertion data to the usage time for the insertion data. Alternatively, the look-ahead interval may be considered to delay the usage time for the insertion data to the availability time of the insertion data. The look-ahead interval may be the maximum difference between the respective usage and availability times of nodes 824, 828, and 832 of FIG. 9. The look-ahead interval may delay the usage times of nodes 824, 828, and 832, such that the delayed usage time for each of nodes 824, 828, and 832 is at or after the respective availability time.
The modification value of node 824 of FIG. 9 for the checksum field 714 of FIG. 7 may become available before the modification value is used. Thus, the TOS field 708 may be stored in a register 840 of FIG. 10A for later generation of this modification value. Because the usage time of the modification value of node 828 for the TTL field 712 may be delayed by the look-ahead interval, the modification value for the TTL field 712 may also need to be stored in a register 840 of FIG. 10A for later use at the delayed usage time. Thus, the storage class for the TOS field 708 and the TTL field 712 may be a register storage class as shown in FIG. 10A.
Because the availability time and the delayed usage time are equal for the insertion data of node 832, the insertion data may be used upon becoming available and no storage register is needed. Thus, a bus on line 842 of FIG. 10B may be used to transfer the insertion data that is read from a memory. It will be appreciated that a field or data read from a memory may be used multiple times including both at availability and after availability. FIG. 10C is a block diagram of a storage class of register 844 with bypass on line 846 that may be employed for a field or memory read data that is used on becoming available and is also used after becoming available.
Those skilled in the art will appreciate that various alternative computing arrangements, including one or more processors and a memory arrangement configured with program code, would be suitable for hosting the processes and data structures of the different embodiments of the present invention. In addition, the processes may be provided via a variety of computer-readable media or delivery channels such as magnetic or optical disks or tapes, electronic storage devices, or as application services over a network.
While particular embodiments of the present invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects and, therefore, the appended claims are to encompass within their scope all such changes and modifications as fall within the true spirit and scope of this invention.

## Claims

1. A processor-based method for creating a hardware description language (HDL) specification of a network packet processor, comprising:
inputting a textual language specification of processing of a type of network packets by the network packet processor, wherein the textual language specification includes at least one memory read action and at least one modification action, each memory read action for reading a stored value from a memory of the network packet processor and each modification action for modifying one of a plurality of fields of the type of network packets;
determining a respective availability, relative to a beginning of the type of network packets, of the fields which are read from the type of network packets for the at least one memory read action and the at least one modification action;
determining a respective availability, relative to the beginning of the type of network packets, of the stored value read from the memory for the at least one memory read action;
determining a look-ahead interval in response to the respective availabilities of the fields that are read from the type of network packets for the at least one modification action and the stored value for the at least one memory read action;
determining respective storage classes for the fields which are read from the type of network packets for the at least one memory read action and the at least one modification action, wherein each respective storage class is one of a bus, a register, and a register with bypass; and
generating the HDL specification of the network packet processor based on the look-ahead interval and the respective storage classes.

2. The processor-based method of claim 1, wherein for each of the at least one memory read action and the at least one modification action with the action including at least one parameter, the fields which are read from the type of network packets for the action include the fields that are read for determining each of the at least one parameter, the parameter being one of a guard condition for enabling and disabling the action, an address of the stored value in the memory for the action that is a memory read action, and a modification value for updating the one of the fields of the type of the network packets for the action that is a modification action.

3. The processor-based method of claim 1, wherein the determining of the respective availability of the fields which are read from the type of network packets for the at least one memory read action and the at least one modification action includes determining the respective availability of each of the fields as a time of the network packet processor receiving the field of the type of network packets relative to the beginning of the type of network packets.

4. The processor-based method of claim 1, wherein the determining of the respective availability of the stored value read from the memory for the at least one memory read action includes generating a dependency graph including, for each of the at least one memory read action, a directed edge for each of the fields which are read from the type of network packets for the memory read action, the directed edge from a node for the field to a node for the stored value read from the memory for the memory read action.

5. The processor-based method of claim 4, wherein the fields which are read from the type of network packets for the memory read action include the fields that are read for determining at least one of an address of the stored value in the memory for the memory read action and a guard condition for enabling and disabling the memory read action.

6. The processor-based method of claim 4, wherein for a first and second memory read action with at least one of an address and a guard condition of the second memory read action determined as a function of the stored value read from the memory for the first memory read action, the dependency graph further includes a directed edge from the node for the first memory read action to the node for the second memory read action.

7. The processor-based method of claim 4, wherein the generating of the dependency graph includes marking the nodes for the fields with the respective availability of the fields, and marking the node for the stored value for each of the at least one memory read action with the respective availability of the stored value read from the memory for the memory read action, the respective availability being a sum of a delay for reading the stored value from the memory for the memory read action and a maximum of the respective availability of each node with an edge directed to the node for the memory read action.

8. The processor-based method of claim 1, further comprising determining a respective scheduling of reading the stored value from the memory for the at least one memory read action, wherein the respective availability of the stored value read from the memory for each of the at least one memory read action is the respective scheduling for the memory read action plus a delay for reading the stored value for the memory read action from the memory.

9. The processor-based method of claim 8, wherein the determining of the respective scheduling of reading the stored value from the memory for each of the at least one memory read action includes determining the respective scheduling as a maximum of the respective availability for each stored value for the at least one memory read action that is used for determining each parameter of the memory read action and the respective availability for each field of the type of network packets that is used for determining each parameter of the memory read action.

10. The processor-based method of claim 1, wherein the determining of the look-ahead interval includes generating a dependency graph including, for each of the at least one modification action, a directed edge for each of the fields which are read from the type of network packets for the modification action, the directed edge from a node for the field to a node for the modification action.

11. The processor-based method of claim 10, wherein the fields which are read from the type of network packets for the modification action include the fields that are read for determining at least one of a modification value for updating the one of the fields of the type of the network packets for the modification action and a guard condition for enabling and disabling the modification action.

12. The processor-based method of claim 10, wherein the generating of the dependency graph includes generating the dependency graph, including, for each of at least one variable, a directed edge to a node for the variable from the node for each of the fields that are read for determining the variable, and a directed edge from a node for the variable to the node for each usage of the variable in the at least one modification action and the at least one variable.

13. The processor-based method of claim 10, wherein the generating of the dependency graph includes marking the nodes for the fields with the respective availability of the fields, and marking the node for each modification action with a respective availability that is a maximum of the respective availability of each node with an edge directed to the node for the modification action.

14. The processor-based method of claim 10, wherein each of the at least one the modification action is one of a set action for setting the one of the fields of the type of network packets to a modification value, an insert action for insertion of data at the one of the fields of the type of network packets, or a remove action for removal of the one of the fields of the type of network packets.

15. The processor-based method of claim 14, wherein the generating of the dependency graph includes generating the dependency graph, including, for each of the at least one modification action that is an insert action, a directed edge to a node for the data of the insert action from the node for each of the fields that are read for determining the data of the insert action, and a directed edge from a node for the data of the insert action to the node for the modification action.

16. The processor-based method of claim 1, further comprising, for each of the at least one modification action, determining a usage timing for the modifying of the one of the fields of the type of network packets for the modification action.

17. The processor-based method of claim 16, wherein the determining of the look-ahead interval includes determining the look-ahead interval as a maximum of the respective availability of the stored value for each of the at least one memory read action and a respective difference for each of the at least one modification action and for each of the fields which are read from the type of network packets for the modification action, the respective difference being the respective availability of the field minus the usage timing for the modifying of the one of the fields of the type of network packets for the modification action.

18. The processor-based method of claim 1, further comprising determining at least one usage timing for each of the fields which are read from the type of network packets for the at least one memory read action and the at least one modification action.

19. The processor-based method of claim 18, wherein the respective storage class for each of the fields which are read from the type of network packet for the at least one memory read action and the at least one modification action is: a bus in response to each usage timing of the field equaling the availability of the field, a register in response to each usage timing of the field not equaling the availability of the field, and a register with bypass in response to one usage timing of the field equaling the availability of the field and another usage timing of the field not equaling the availability of the field.

20. Processor-readable device embodied in a program storage medium and configured with executable instructions for creating a hardware description language (HDL) specification of a network packet processor, wherein execution of the instructions by one or more processors causes the one or more processors to perform operations including,
inputting a textual language specification of processing of a type of network packets by the network packet processor, wherein the textual language specification includes at least one memory read action and at least one modification action, each memory read action for reading a stored value from a memory of the network packet processor and each modification action for modifying one of a plurality of fields of the type of network packets;
determining a respective availability, relative to a beginning of the type of network packets, of the fields which are read from the type of network packets for the at least one memory read action and the at least one modification action;
determining a respective availability, relative to the beginning of the type of network packets, of the stored value read from the memory for the at least one memory read action;
determining a look-ahead interval in response to the respective availabilities of the fields which are read from the type of network packets for the at least one modification action and the stored value for the at least one memory read action;
determining respective storage classes for the fields which are read from the type of network packets for the at least one memory read action and the at least one modification action, wherein each respective storage class is one of a bus, a register, and a register with bypass; and
generating the HDL specification of the network packet processor based on the look-ahead interval and the respective storage classes.