Bug in reading bytes/halfwords

[Jason Lowe-Power]

From @cjnitta:

Jason,
A student pointed out that there might be a bug in the memory.scala.
Starting on line 73, it might need to be:

     when (maskmode =/= 2.U) { // When not loading a whole word
       val offset = io.dmem.address(1,0)

       when (maskmode === 0.U) { // Reading a byte
         readdata := (memory(io.dmem.address >> 2) >> (offset * 8.U)) & 
0xff.U
       } .otherwise {
         readdata := (memory(io.dmem.address >> 2) >> ((offset & 0x2.U) 
* 8.U)) & 0xffff.U
       }
     } .otherwise {
       readdata := memory(io.dmem.address >> 2)
     }

The difference was the shifting down of the byte or half word. It didn't
seem to be a problem in the first 3 projects so far.

Chris

---

I think both lines could be >> (offset * 8.U) since the halfword must be 16-bit aligned.

[Jason Lowe-Power]

@deyahruhd. This is a bug in your code, too :).

[Jason Lowe-Power]

Does anyone remember if this has been fixed?

[Jared Barocsi]

This should be fixed in the memory port modules.