In the hard drive controller card market - the higher-end (LSI, 3Ware) cards have their own on-board CPU and RAM, and take care of interacting with the hard drive, only notifying the system's CPU after the data has been transferred completely.
Is there a card that provides equivalent functionality for USB peripherals? (So that multi-gigabyte data transfers to a USB-connected device would have negligible CPU overhead, as with the above-mentioned SAS/SATA cards?
I'm aware that a cheap card can support DMA. And that 1394 cards can support DMA. I'm inquiring about the existence a card that fully implements the protocol, manages the bus, and transfers the data itself, only handing off data blocks to the host OS when they're fully off the wire.