Traffic generator using parallel coherent transmit engines

1. A packet generator to transmit a data flow, comprising:

a plurality of parallel transmit engines to generate packets for transmission

a multiplexer to coherently interleave packets generated by the plurality of transmit engines to form the data flow

a schedule and overlay engine

wherein the schedule and overlay engine provides packet forming data to the plurality of transmit engines and provides packet sequence data to the multiplexer, the packet forming data including a stream identifier and overlay data for each packet

wherein each transmit engine further comprises

a template memory storing a plurality of packet templates associated with a corresponding plurality of streams

a background engine to select a packet template from the template memory in accordance with the stream identifier

an overlay fill engine to insert the overlay data into the selected packet template.

2. The packet generator of claim 1 , wherein the packet forming data for each packet further includes one or more of a packet length, and payload instructions.

3. The packet generator of claim 1 , wherein each transmit engine further comprises a front end engine including a checksum calculator.

4. The packet generator of claim 1 , wherein the multiplexer further comprises:

a plurality of FIFO buffers, each FIFO buffer coupled to receive packets from a corresponding one of the plurality of transmit engines

a data selector to retrieve packets from the plurality of FIFO buffers to form the data flow.

5. The packet generator of claim 4 , wherein the multiplexer further comprises:

another FIFO buffer coupled between the schedule and overlay engine and the data selector to hold the packet sequence data.

6. The packet generator of claim 4 , wherein the multiplexer further comprises:

a real time clock

a timestamp engine coupled between the data selector and a network interface unit to add a timestamp in accordance with the real time clock to at least some of the packets prior to transmission via the network interface unit.

7. The packet generator of claim 6 , wherein

the packet sequence data includes a target transmit time, and

wherein the multiplexer outputs each packet at the corresponding target transmit time as indicated by the real time clock.

8. The packet generator of claim 1 , wherein

the multiplexer outputs the data flow at a first data rate, and

the transmit engines generate packets at a second data rate lower than the first data rate.

9. The packet generator of claim 8 , wherein

the second data rate is equal to the first data rate divided by the number of transmit engines in the plurality of transmit engines.

10. The packet generator of claim 1 , wherein coherently interleaved packets are added to the data flow in a sequence determined prior to the generation of the packets.

11. A method of generating a packet flow, comprising:

providing packet forming data to a plurality of transmit engines, the packet forming data including a stream identifier and overlay data for each packet

providing packet sequence data to a multiplexer

the plurality of transmit engines generating packets, wherein generating each packet further comprises

retrieving a template associated with the steam identifier from a template memory storing a plurality of templates respectively associated with a corresponding plurality of streams

inserting the overlay data into the retrieved template

the multiplexer coherently interleaving packets generated by the plurality of transmit engines to form the packet flow in accordance with the packet sequence data.

12. The method of generating a packet flow of claim 11 , further comprising:

storing definitions for the plurality of streams

determining, from the stored definitions, a packet sequence

generating the packet sequence data indicating the order in which packets from the plurality of packet streams are to be interleaved to form the packet sequence

identifying a next packet in the packet sequence

assigning the next packet to one of the plurality of transmit engines.

13. The method of generating a packet flow of claim 12 , wherein the assigning further comprises

determining the stream identifier of the next packet

determining a length of the next packet

determining the overlay data for the next packet

providing the packet forming data including the stream identifier, the length, and the overlay data to the assigned transmit engine.

14. The method of generating a packet flow of claim 12 , wherein the coherently interleaving further comprises:

storing the packets generated by the plurality of transmit engines in a corresponding plurality of FIFO buffers

selecting packets for transmission from the plurality of FIFO buffers in accordance with the packet sequence data.

15. The method of generating a packet flow of claim 14 ,

wherein generating the packet sequence data includes setting target transmit times for at least some of the packets, and

wherein coherently interleaving includes transmitting packets at the respective target transmit times.

16. The method of generating a packet flow of claim 11 , wherein coherently interleaving comprises adding packets to the data flow in a sequence determined prior to the generation of the packets.