You have to be careful when specifing a memory size on
the ss10/20 because a SIMM slot uses 64M reguardless of
the actual size of the SIMM. A smaller size will be mirrored
to fill the entire space and OBP checks for mirrioing to
determine the actual size. QEMU doesn't do any mirroring
for small SIMMS which will confuse OBP. I don't think
that is the issue are seeing but just something to keep in mind.
It's not an issue for SS-10/20, but may be an issue for SS-5 and
below. SS-5 and earlier support maximal SIMM size of 32M. It doesn't
seem to be reflected in hw/sun4m.c .