Providing real-time control data for a network processor

This invention relates to controlling parallel processor arrays.

Many modern routers use application specific integrated circuits (ASIC's) to perform routing functions. The ASIC's can be designed to handle the protocols used by the networks connected to the router. In particular, the ASIC's can route high provide high performance routing for data packets having one of a preselected set of protocols.

According to one aspect of the invention, a processor includes a module configured to collect status data, one or more processing engines, and a push engine. The status data is collected from devices connected to a bus. The status data indicates readiness of the devices to participate in data transfers over the bus. The processing engines schedule transfers of data packets between the processor and the devices. The push engine performs unsolicited transfers of a portion of the status data to the processing engines in response to the module collecting new status data.

FIG. 1 is a block diagram of a router based on a parallel processor;

FIG. 2 is a block diagram of a FIFO bus interface of the parallel processor of FIG. 1 ;

FIG. 3 is a block diagram of one of the parallel processing engines used by the processor of FIG. 1 ;

FIG. 4 is a block diagram of a MAC port coupled to the parallel processor of FIG. 1 ;

FIG. 5A shows the status registers for receive-status data;

FIG. 5B shows the status registers for transmit-status data;

FIG. 5C shows the transmit FIFO buffer located in the FIFO bus interface of FIG. 2 ;

FIG. 6 is a flow chart showing a process for providing ready-status data to scheduler threads;

FIG. 7 is a flow chart showing a process for collecting ready-status data from the MAC devices;

FIG. 8 is a flow chart for a process for transferring newly collected ready status data to the scheduler threads; and

FIG. 9 is a flow chart for a process that performs data transfers responsive to ready status data.

FIG. 1 is a block diagram of a router 10 that uses a parallel processor 12 , a set of media access chip (MAC) devices 14 , 14 ′, 14 ″, and a FIFO bus 16 . The router 10 performs data switching between source and destination networks 18 , 18 ′, 18 ″ connected to the MAC devices 14 , 14 ′, 14 ″. The MAC devices 14 , 14 ′, 14 ″ are bridges that couple external networks 18 , 18 ′, 18 ″ to the FIFO bus 16 . The processor 12 can execute software to control data routing. By basing control on software, the processor 12 may be more easily modified to accommodate new protocols or data characteristics.

The router 10 performs data routing in two stages. First, one of the MAC devices 14 , 14 ′, 14 ″ connected to the source network 18 , 18 ′, 18 ″ transmits a data packet to the parallel processor 12 via the FIFO bus 16 . Second, the parallel processor 12 retransmits the data packet over the FIFO bus 18 to the MAC device 14 , 14 ′, 14 ″ connected to the destination network 18 , 18 ′, 18 ″. The data transmissions over the FIFO bus 16 employ 64-byte data packets and proceed via an Ethernet protocol.

The parallel processor 12 has a parallel data forwarding structure that includes an array of identical processing engines 22 a - 22 f . Each processing engine 22 a - 22 f has an internal structure for executing a plurality of, e.g., four, independent threads.

Referring to FIGS. 1 and 2 , the processing engines 22 a - 22 f process data packets received from the MAC devices 14 , 14 ′, 14 ″. To process a data packet, one of the processing engines 22 a - 22 f looks up routing information in a synchronous random-access memory (SRAM) 24 using information from the packet header. The processing engines 22 a - 22 f also move the data packets from a FIFO buffer 58 to a queue in a synchronous dynamic random-access memory (SDRAM) 26 . The FIFO buffer 58 temporarily stores data packets received from the MAC devices 14 , 14 ′, 14 ″. The various queues located in the SDRAM 26 are classified by destination MAC device 14 , 14 ′, 14 ″ and retransmission priority.

The processing engines 22 a - 22 f also process data from the queues of the SDRAM 26 . This processing includes moving data packets from the queues of the SDRAM 26 to a FIFO buffer 60 . The FIFO buffer 60 temporarily stores data prior to retransmission to the MAC devices 14 , 14 ′, 14 ″ over the FIFO bus 16 . Along with the data, associated control and destination information are stored in the FIFO buffer 60 for use in transmitting the data. The associated data is 16 bytes wide.

The SRAM 24 and SDRAM 26 couple to the processing engines 22 a - 22 f through respective SRAM and SDRAM controllers 34 , 36 . The SRAM controller 34 has content addressable memory that supports look ups of identification information on the queues of the SDRAM 24 . The look-ups use header data from received data packets. The SDRAM controller 36 coordinates data writes to and reads from the queues of the SDRAM 24 that store received data packets.

The parallel processor 12 has several internal busses 39 , 40 , 41 . An S bus 39 couples the processing engines 22 a - 22 f to a FIFO bus interface 38 (FBI) and to the SRAM controller 34 . An M bus 40 couples the processing engines 22 a - 22 f and the FBI 38 to the SDRAM controller 36 and the SDRAM 26 . An AMBA bus 41 couples a processor core 44 to the processing engines 22 a - 22 f and the FBI 38 .

The FBI 38 controls data transfers on the FIFO bus 16 and collects status data on the readiness of the ports 28 , 30 , 32 of the MAC devices 14 , 14 ′, 14 ″ to participate in data transfers over the FIFO bus 16 . The ready status data is collected from the MAC devices 14 , 14 ′, 14 ″ through a ready bus 42 , which is also controlled by the FBI 38 .

Referring again to FIG. 1 , the processor core 44 uses software to perform a variety of functions. The functions may include data packet routing, exception handling, queue management, monitoring of data packet transfers, supporting network management protocols and/or providing local area network emulation.

The parallel processor 12 includes a PCI bus interface 46 that couples to a PCI bus 48 . The PCI bus 48 can support communications between the parallel processor 12 and external processors. The other processors may control and/or reprogram the processor core 44 or other components 22 a - 22 f , 38 of the multiprocessor 12 .

Referring again to FIG. 2 , the connections between the FBI 38 and the processing engines 22 a - 22 f are shown. The FBI 38 includes a control module 50 for the ready bus 42 and a push engine 62 . The control module 50 periodically collects receive-ready status data and transmit-ready status data from the MAC devices 14 , 14 ′, 14 ″. The collected ready status data is stored in a set of status registers 54 . The set includes separate registers for storing receive-ready status data and transmit-ready status data. The push engine 62 regularly sends the ready status data over the S bus 39 to scheduler threads located in the processing engines 22 a - 22 f in response to commands from logic internal to the FBI 38 .

The processing engines 22 a - 22 f include separate receive-scheduler and transmit-scheduler threads. The receive-scheduler thread schedules the processing of data received from the FIFO bus 16 . The transmit-scheduler thread schedules the processing of data to be transmitted to the FIFO bus 16 .

The receive-scheduler thread assigns data forwarding and header processing tasks to other threads in the processing engines 22 a - 22 f . These tasks include sharing operation of a push engine 62 that transports data from the receive FIFO buffer 58 in the FBI 38 to one of the storage queues in the SDRAM 26 .

The transmit-scheduler thread also assigns data forwarding tasks to other threads in the processing engines 22 a - 22 f . These tasks include sharing in operation of a pull engine 64 , which moves data from the storage queues in the SDRAM 26 to the transmit FIFO buffer 60 . The tasks also include directing the pull engine 62 to write transmission control and MAC device 14 , 14 ′, 14 ″ address information to the FIFO buffer 60 . Each data packet in the transmit FIFO buffer 60 has associated address and control information that control the retransmission over the FIFO bus 16 .

To control data forwarding by the push and pull engines 62 , 64 , the execution threads of the processing engines 22 a - 22 f send commands signals to FIFO command queues 66 , 68 via a line 70 . Components of the FBI 38 can also send commands to the command queues 66 , 68 of push and pull engines 62 , 64 . For example, the ready bus controller 50 can send a command to the queue 66 that causes the push engine 62 to transfer ready status data from the status registers 54 to the processing engines 22 a - 22 f . An arbiter 56 controls transmission of commands from the queues 66 , 68 to the push and pull engines 62 , 64 .

The push and pull engines 62 , 64 perform several types of tasks. The push and the pull engines 62 , 64 are involved in bi-directional forwarding of data packets between the FIFO buffers 58 , 60 and the SDRAM controller 36 . The push and pull engines 62 , 64 also operate a large hardware unit 71 located in the FBI 38 . The push engine 62 also forwards ready status data from the set of status registers 54 to the receive- and transmit-scheduler threads located in the processing engines 22 a - 22 f.

The hardware unit 71 performs various operations for the execution threads of the processing engines 22 a - 22 f and includes a hash unit 72 and a scratchpad memory 73 . The execution threads operate the hardware unit 71 by sending commands to the queues 66 , 68 . To perform the operations, the pull engine 64 retrieves input data over the S bus 39 from output transfer registers 80 a - 80 f of the requesting processing engine 22 a - 22 f . The pull engine 64 moves the retrieved data and associated commands to the hardware unit 71 . The hardware unit 71 forwards results from the operations to the push engine 62 . The push engine 62 uses command information from the command queue 66 and/or pull engine 64 to transmit the results back over the S bus 39 to input transfer registers 78 a - 78 f of the requesting or destination processing engine 22 a - 22 f.

Referring to FIG. 3 , one embodiment 74 of the processing engines 22 a - 22 f is shown. The processing engines 22 a - 22 f have input/output terminals 75 - 77 for control signals, address signals, and data. Control signals, address signals, and data are transferred to and from the processing engines 22 a - 22 f over three busses, i.e., the M bus 40 , the S bus 39 , and the AMBA bus 41 . The address signals identify both a processing engine 22 a - 22 f and an execution thread so that external commands can independently address different threads. Data is received at and transmitted from respective input and output transfer registers 78 , 80 . Each input and output transfer register 78 , 80 is assigned to an individual execution thread. To write data to or read data from a particular execution thread, an external device accesses one of the transfer registers 78 , 80 assigned to the particular thread.

Referring to FIG. 4 , the port 28 of the MAC device 14 is shown. The port 28 has transmit and receive FIFO buffers 90 , 92 for storing data prior to transmission to and after reception from the FIFO bus 16 , respectively. Both buffers 90 , 92 have entries of fixed size that are multiples of 64 bytes, i.e., the size of data packets on the FIFO bus 16 . The port 28 also includes address decoders and a controller 94 . The controller 94 controls both protocol transfers over the FIFO bus 16 and responses to ready status queries from the ready bus 42 . The responses to the queries indicate whether the transmit buffer 90 has a 64 byte data packet to transmit and/or whether the receive buffer 92 has space to receive a 64 byte data packet.

The various ports 28 , 30 , 32 of the MAC devices 14 , 14 ′, 14 ″ may support different data transfer rates. The ports 28 , 30 of the MAC devices 14 , 14 ′ support transfer rates of about ten or one hundred megabits of data per second. The port 32 of the MAC device 14 ″ may have a transfer rate of up to about one gigabit per second.

The ready bus 42 includes control/address and data lines. The control/address lines enable selection of a transaction type and a port 28 , 30 , 32 of the MAC devices 14 , 14 ′, 14 ″. The data line transfers receive-ready status data and transmit-ready status data to the FBI 38 in response to status queries from the control module 50 for the ready bus 42 .

Referring to 5 A, the registers R 1 , R 2 , R 3 that store receive-ready status data are shown. The registers R 1 and R 2 store receive-ready status data for individual MAC ports 28 , 30 , 32 . The readiness of each MAC port 28 , 30 , 32 to transmit a data packet to the FIFO bus 16 is indicated by the value of an associated bit or flag stored in one of the registers R 1 , R 2 . One logic value of the bit or flag indicates that the associated port 28 , 30 , 32 has a data packet ready to transmit, and the other logic value indicates the associated port 28 , 30 , 323 has no ready data packets. Different ports 28 , 30 , 32 may have data packets of different sizes, but the receive scheduler thread knows the packet size associated with each port 28 , 30 , 32 .

The registers R 2 and R 3 have 32 bits each and thus, can accommodate receive-ready status data for up to 64 different MAC ports 28 , 30 , 32 .

The register R 3 stores a cyclic counter value, which acts as a time stamp for the receive-status data stored in registers R 1 , R 2 . The counter value is incremented each time new receive-status data is collected. By comparing the counter value to a previously received counter value, the scheduler thread can determine whether the present receive-status data is new or stale, i.e., whether the data has already been seen.

Referring to FIG. 5B , the registers R 4 , R 5 , R 6 that store transmit-ready status data are shown. The registers R 4 and R 4 store transmit-ready status data for individual MAC ports 28 , 30 , 32 . Each MAC port 28 , 30 , 32 has an associated bit or flag in one of the registers R 4 and R 4 . One logic value of the bit or flag indicates that the associated port 28 , 30 , 32 has enough space to receive a data packet, and the other logic value indicates the associated port 28 , 30 , 32 does not have enough space.

The registers R 4 and R 5 have a total of 64 bits and thus, can report transmit ready status for up to 64 MAC ports 28 , 30 , 32 .

Referring to FIG. 5C , the number stored in register R 6 indicates the position of a remove pointer 96 in the transmit FIFO buffer 60 . For an embodiment in which the transmit FIFO buffer 60 has sixteen entries, the position of the remove pointer is represented as a 4-bit number.

Since the FBI 38 transmits 64-byte data packets from the buffer 60 according to a FIFO scheme, the remove pointer 96 indicates which data packets are scheduled but not transmitted. The position of the pointer 96 can be used to determine which MAC ports 28 , 30 , 32 have been scheduled to receive a data packet but have not yet received a data packet. Such ports 28 , 30 , 32 may have status data in registers R 4 , R 5 indicating an availability to receive a data packet even though the available space has already been assigned to a waiting data packet.

The transmit scheduler thread can use the position of the remove pointer 96 to interpret transmit-ready status data of the registers R 4 , R 5 . From the position of the remove pointer 96 , the transmit scheduler thread identifies MAC ports 28 , 30 , 32 already scheduled to receive a data packet. The transmit scheduler thread does not schedule a new data packet for such ports, because the waiting and already scheduled data packet may take the available space therein.

In the parallel processor 12 , the collection of ready status data is asynchronous with respect to scheduling of data packet transfers. The asynchronous relationship enables both the collection of ready status data and the scheduling of data packets to have higher effective bandwidths. The asynchronous relationship also introduces some unpredictability into latencies associated with the transfer of newly collected ready status data to scheduler threads.

Referring to FIG. 6 , a process 100 by which the FBI 38 provides ready status data to the scheduler threads is shown. The FBI 38 performs 102 a collection cycle in which new ready status data is obtained from the MAC devices 14 , 14 ′, 14 ″ interactively via the ready bus 42 . In response to completing the collection cycle, the FBI 38 performs an unsolicited transfer 104 of the newly collected ready status data to the input transfer registers 78 a - 78 f assigned to the scheduler threads. In an unsolicited data transfer, the destination device for the transfer does not request the transfer. The transfer of ready status data from the FBI 38 to destination processing engines 22 a - 22 f and scheduling threads proceeds without any request from the processing engines 22 a - 22 f . Instead, the FBI 38 automatically performs the transfer in response to finishing a collection cycle for the ready status data. The completion of each collection cycle causes issuance of a command to the push engine 62 , which transfers the ready bus data to the processing engines 22 a - 22 f . After completing the transfer, the FBI 38 loops back 106 to collect new ready status data.

Making transfers of new ready status data unsolicited lowers latencies for delivering such data to scheduler threads. Since latencies in delivering such data can cause scheduling errors, making the transfer of ready status data unsolicited can lower numbers of occurrences of scheduling errors.

Referring to FIG. 7 , a process 110 by which the FBI 38 collects ready status data is shown. Separate collection cycles are performed to collect receive-ready status data and to collect transmit-ready status data. Each collection cycle also initiates an unsolicited transfer of at least a portion of the collected ready status data to the processing engines 22 a - 22 f.

To start a new collection cycle, the control module 50 for the ready bus 42 selects 112 the addresses to be polled for ready status data. The selection may be for all addresses of the MAC ports 28 , 30 , 32 connected to the FIFO bus 16 or for a sub-range of the addresses. If a sub-range is selected, the collection of new ready status data spans several cycles, a portion of the MAC ports 28 , 30 , 32 being polled in each cycle. The sub-range polled in collection cycles may be programmed into the processor core 44 or the FBI 38 .

The control module 50 polls 114 by sending status queries over the ready bus 42 to the selected ports 28 , 30 , 32 of the MAC devices 14 , 14 ′, 14 ″. In response to the queries, the control module 50 receives 116 new ready status data from the polled ports 28 , 30 , 32 . A response to a query for receive-ready status data indicates whether the responding port 28 , 30 , 32 has a data packet ready to transmit. A response to a query for transmit-ready status indicates whether the responding port 28 , 30 , 32 has space available to receive another data packet.

The control module 50 writes 118 new ready status data, which has been from the responses, to the status registers R 1 , R 2 , R 4 , R 5 , shown in FIGS. 5A-5B . The control module 50 also increments 120 the counter value in status register R 3 . Incrementing the counter value updates the time stamp associated with the newly collected ready status data. After updating the time stamp, the FBI 38 performs an unsolicited transfer of the newly collected ready status data to the scheduler threads located in processing engines 22 a - 22 f.

The FBI 38 transmits 126 data packets from the transmit FIFO buffer 60 asynchronously with respect to the collection of ready status data from the MAC devices 14 , 14 ′, 14 ″. In response to each transmission, the FBI 38 advances 128 the remove pointer 96 of the transmit FIFO buffer 60 and writes 130 the new position of the remove pointer 96 to status register R 6 . The number stored in the status register R 6 reflects the present position of the remove pointer 96 of the transmit FIFO buffer 60 .

Referring to FIG. 8 , a process 140 by which the FBI 38 transfers receive-ready and transmit-ready status data to the respective receive and transmit scheduler threads is shown. The FBI 36 transfers the ready status data via the S bus 39 when the S bus 39 is not being used for communications with the SRAM controller 34 .

Completion of a collection cycle enables 142 the push engine 62 to transfer ready status data from the status registers 54 to the appropriate execution threads, i.e., scheduler threads. The push engine 62 reads 144 both a value for the number of the status registers R 1 -R 3 or R 4 -R 6 to be transferred and the identity of the target scheduler thread. One, two, or three status registers may be transferred in one cycle. The count and identity of the scheduler threads, i.e., for both the thread and the associated processing engine 22 a - 22 f , are stored in control registers 52 .

Transfers of 1, 2 or 3 of the status registers R 1 -R 6 write to the 1, 2 or 3 lowest consecutive input transfer registers 78 a - 78 f assigned to the target scheduler thread. But, the transfers may also alternate targeting of the input transfer registers 78 a - 78 f . To alternate targets, the push engine 62 sends consecutive transfers to different input transfer registers 78 a - 78 f assigned to the same scheduler thread. For example, a first transfer of two of the status registers R 1 -R 3 could be written to the two lowest input transfer registers, and the next transfer would then be written to the two next-lowest input transfer registers. From the count and alternate-select status, the push engine 62 determines 146 which input transfer registers 78 a - 78 f to write during the transfer.

The push engine 62 transmits 148 a transfer protect control signal to the target input transfer registers 78 a - 78 f . The transfer protect signal protects the target transfer registers 78 a - 78 f against read-write conflicts during transfers. The transfer protect signal blocks reads of the registers 78 a - 78 f by the associated scheduler threads. While protected from such reads, the push engine 62 writes 150 the new ready status data to the input transfer registers 78 a - 78 f.

After completing a transfer of ready status data, the push engine 62 stops 152 transmitting the transfer protect signal. When the protect signal is no longer asserted, the scheduler threads can read the input transfer registers 78 a - 78 f . The scheduler threads reads the ready status data from the input transfer registers 78 a - 78 f in the order written to avoid other read-write conflicts.

Referring to FIG. 9 , a process 160 that performs data transfers responsive to ready status data is shown. To schedule a transfer, the appropriate scheduler thread determines 162 which MAC ports 28 , 30 , 32 are available from the values of the new ready status data. For the available ports 28 , 30 , 32 , the scheduling thread selects 164 an available execution thread to handle the data transfer and signals the selected thread. The selected thread and FBI 38 perform the scheduled data transfer 166 the scheduled data transfer.

For receive-ready status data, the scheduler thread also compares the time stamp of the status data to the time-stamp of time stamps of previous receive-ready status data. If the time stamp has an old value the ready status data is stale, and the receive scheduler thread stops without scheduling data transfers. Otherwise, the receive scheduler thread proceeds as described above.

For transmit-ready status data, the scheduler thread uses present values of the remove pointer 96 to determine whether any of the available ports are already scheduled to receive a data packet. Any such devices are not scheduled for another data transmission.

While various embodiments have been described in the detailed description, the description is intended to illustrate and not to limit the scope of the invention, which is defined by the appended claims. Other aspects, advantages, and modifications are within the scope of the claims.