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Added mem_wstrb documentation

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Clifford Wolf 2016-04-03 17:14:07 +02:00
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commit 3ccbf6877e
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@ -319,6 +319,11 @@ In a write transfer `mem_wstrb` is not 0 and `mem_rdata` is unused. The memory
write the data at `mem_wdata` to the address `mem_addr` and acknowledges the
transfer by asserting `mem_ready`.
The 4 bits of `mem_wstrb` are write enables for the four bytes in the addressed
word. Only the 8 values `0000`, `1111`, `1100`, `0011`, `1000`, `0100`, `0010`,
and `0001` are possible, i.e. no write, write 32 bits, write upper 16 bits,
write lower 16, or write a single byte respectively.
There is no need for an external wait cycle. The memory can acknowledge the
write immediately with `mem_ready` going high in the same cycle as
`mem_valid`, or `mem_ready` being tied to constant 1.