Memory-Mapped Input-Output (MMIO)

Like PIO, but the FIFO is directly memory mapped. Again, this means more to x86 as it has the wierd I/O vs. memory distinction that 68k, etc. do not have. The FIFO is of fixed length and writes to successive locations are writes "further down" the FIFO. Also, MMIO allows a set of registers to be directly addressed by location where in the PIO system they would be addressed by "write to register # to address register, write/read data to/from data register, repeat" kind of system. MMIO is genearlly simpler to program for than PIO, but PIO is a lot easier to design hardware for.