[ajross]

"Big" hardware like a USB3 controller or the NVMe controller in the linked article actually looks more like software than hardware anyway, to be truthful. The devices have their own processors and accept commands that look like a software protocol: you put a linked list of these structs/headers/commands into memory, which reference buffers at these addresses via pointer, then turn the device on by writing to this register over here. As the device finishes, it signals completion with a given struct by putting a message into this output buffer (or by setting its "active" field to false, maybe), etc...

The only bits you need to worry about that looks like hardware are getting the correct physical addresses filled in, and on some platforms worring about memory ordering and/or cache management to be sure the device sees the same memory state you think it does.