24 Apr
2020
24 Apr
'20
12:16 p.m.
Oh, right. Still, it sounds from reports here like
regular DMA doesn't work
in QBUS mode either - and technically that table entry might mean than since
it doesn't work for the QBUS _at all_, that includes no block mode.
Regular Q bus DMA seems to be working fine. I can see the performance
difference pretty easily when looking at 1,2,4,8,16 word transfers,
anything else I should be checking?
I actually have -B/-C boards, I should plug one in in
QBUS mode, and get my
QSIC prototype working again (it somehow random failed during the last year,
and I've been too lazy to debug it), and write a little program to DMA blocks
in and out, and see what happens to the data. If I get really energetic I
could throw a 'scope on the bus and look at bus cycles and see if they look
OK.
I can also bring up an RL02 with the RLV12 (also does DMA) and see how
an authentic DEC appliance works with this memory card. But really I'm
not seeing any speed increase of PMI memory vs. non-PMI memory with the
exception that the initial memory check runs a good bit faster with PMI
over without.
And that might make sense: PMI memory responds to the Q bus just like
normal memory. So from a Q bus device perspective it's just boring old
memory and thus no speed improvement. What might speed up is if I did
memory to memory (VM0:) copies, but with only 2mb running at the moment
there's not a lot of time to check for performance differences.
Maybe it can't properly handle things like 18 bit DMA cards like the RXV12.
Let's find out: What's the worst that can happen?