[Libre-soc-dev] mulhw / mulhwu in microwatt updates SO

Luke Kenneth Casson Leighton lkcl at lkcl.net
Wed Sep 2 18:37:09 BST 2020

paul, mikey, benjamin, hi:

attached a revised "signed-off" (git am apply formatted) patch to add
XER and CR debug reporting.

also heads-up on this:

in the side-by-side, instruction-by-instruction examination of
microwatt-libresoc execution of 1.bin, it's become evident that having
XER and CR DMI reporting is absolutely essential.  it often takes a
good 10-15 minutes to read microwatt core_tb log files trying
desperately to work out which pipelined overlapping output (attached
patch) is associated with the instruction that occurred pages and
pages beforehand: when there are multiple instructions all reading and
writing to CR and XER it becomes hell (and as you saw last week i make
mistakes in this manual analysis process).

i've already added it to libresoc (addresses 0b1000 for CR, 0b1001 for
XER) and Cole would like to have a go at adding DMI support to
microwatt for CR reading.

both of us have been reading VHDL now for long enough to be able to
consider doing this.

the XER read is not ready for submission as we would need to work out
if it's just those SO/CA/OV bits or if the remaining bits (in the SPR
regfile file) that should also be included.  basically if that's the
case then the code from OP_MFSPR needs duplicating (the construction
of XER).  becomes much more relevant when FP is added as there are
several more (relevant) bits.


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