Intel PXA255 Developer's Manual page 509

MultiMediaCard Controller
The MMC controller is the interface between the software and the MMC bus. It is responsible for
the timing and protocol between the software and the MMC bus. It consists of control and status
registers, a 16-bit response FIFO that is eight entries deep, two 8-bit receive data FIFOs that are 32
entries deep, and two 8-bit transmit FIFOs that are 32 entries deep. The registers and FIFOs are
accessible by the software.
The MMC controller also enables minimal data latency by buffering data and generating and
checking CRCs.
Refer to Section 15.4 for examples.
Intel® PXA255 Processor Developer's Manual 15-5