23 Dec
2013
23 Dec
'13
11:30 a.m.
On Mon, Dec 23, 2013 at 2:04 PM, Peter Corlett <abuse at cabal.org.uk> wrote:
On Mon, Dec 23, 2013 at 01:05:44PM -0500, Ethan Dicks
wrote:
[...]
I think you'd need a lot of external hardware to do that when your choices
for SCSI chips were the 5380 or 33C93 - 8-bit chips for an 8-bit SCSI bus
on a 16-bit 68000 bus that did byte transfers in a funny way (I've hung
$20,000 bus analyzers off of the 68K looking for a hardware bug the designer
claimed was a bug in my firmware - he swapped UDS and LDS and
because of how the 68K is built internally, somethings worked and somethings
failed... so I'm pretty sure I'm on firm ground saying it's not practical
to try to make MOVEM work with an 8-bit peripheral - anything is
possible, but elaborate schemes are often more expensive than just
doing it the right way in the first place).
-ethan
My first several SCSI interfaces for the Amiga
were PIO and could only
transfer a couple hundred Kbytes/sec. I knew how they worked from my time
writing embedded 68000 code with transfer loops and was not surprised at
their speed.
If you had contrived the hardware design to have suitable incomplete decoding,
you could have exploited the movem hack that copies 56 bytes in 72 cycles,
which would give you north of 5MB/s on a 7.09MHz CPU.