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---------------------------- SDRAM READ/WRITE PIPE -----------------------------
A front-end for the SDRAM controller which allows block reads and writes through
a pair of 16-bit data-valid-ready pipes. Commands and write-data are sent down
the cmd pipe and read-data is returned on the rsp pipe. There is an auto-
increment pointer which is used during read and write operations.
The commands on the cmd pipe look like this:
CCDD DDDD DDDD DDDD <args>
Where CC:
00 -> Update pointer with these 14 bits D and the following 16-bits, giving
a maximum pointer width of 30 bits
01 -> Read a block of 16-bit words N given by the 14 bits D and the following
16 bits (max block size 2^30). Subsequently, 2N data bytes need to be
read from rsp_fifo.
10 -> Write a block of 16-bit words N given by the 14 bits D and the following
16 bits (max block size 2^30). Subsequently, 2N data bytes need to be
written to cmd_fifo.