[KMag]

To get such changes reliably with low latency, I presume you were modifying the DMA buffer, without any syscalls or other mechanisms to synchronize between the CPU and the NIC's processor(s), right? Did you just set up the race condition such that when you got bitten, it resulted in a failed checksum, or was the time window so large that in practice the race condition never bit you?

[pjc50]

It was in a ridiculously expensive 10Gbit ethernet switch with an FPGA built in. Having to write trading algos in Verilog was an extra layer of difficulties.

I don't think it stored the packet at all, just advanced a state machine as each word arrived from the MAC.