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).
Thanks. This got me curious enough that I'm now reading the datasheet. It seems exciting enough that I may likely choose it for my next project that requires a microcontroller. (When I don't want to use FPGAs, which I tend to overuse because I'm a big fan of them, and because cost margins usually don't matter private projects.)