The DMA Sniffer is part of the RP2040 DMA engine. It can perform a variety of functions on the DMA'd data, including CRCs, accumulation, bit-reversal, etc. I use the accumulation function to increment the address contained in the HyperRAM command packet after each scan line is DMA'd from HyperRAM to the scan line buffer. This allows re-use of the HyperRAM command packet, eliminating the need for a per scan line packet (3 uint_32s per scanline). Important for the emulator, as it runs out of RP2040 RAM (vs. flash).

Maybe you'd like to help me get this over the finish line? I'm looking at a steep learning curve, trying to write a Lance chip emulator. I have been able to get LWIP to run on the DECstation HW. (Though Rev 2.1 does exhibit some packet drops which I'm looking at. Hopefully, there's some slight difference between the LAN8720a on the Waveshare boards, and the LAN8742 on rev 2.1 that needs some software...)