8 Jun
2010
8 Jun
'10
1:32 p.m.
From: "Don North" <ak6dn at mindspring.com>
Sent: Tuesday, June 08, 2010 10:08 PM
To: <cctalk at classiccmp.org>
Subject: Re: yet another pdp-8 in a fpga, but this time running tss/8
I have the RX8e/RX01 controller passing the DIRXA
diagnostic now, and am
in the processing of implementing the backing store on the SD card, so
hopefully in the next few weeks I'll get to boot an OS8 image from a
floppy image.
Don
PS: BTW for those ever considering implementing an RX floppy interface
for the PDP8 and want to run diagnostics, I did find a coding error in
the DIRXA (both rev C and D) diagnostics. In one specific test the XDR
IOT is being issued before checking for transfer request via the XTR
IOT. There is a simple patch to the diagnostic to fix it. Turns out it
runs OK on real hardware because the speed difference of a real PDP8e vs
a real RX01/2 controller, but if you speed up the RX controller past a
certain point the test will always fail.
Thanks Don, that might be useful information!
I hope to return to my 6809-based pdp8/e soon, to finish the RX01
emulation code. My 6809-based pdp8/e actually runs OS/8, but
don't speak about speed! This thing is approx 60x slower than a
real pdp8/e (if I can trust the timing mentioned in the diagnostics).
So I probably will not have issues with the bug in DIRXA :-)
Following this FPGA thread with much interest. I have a XESS board
for some 3 years now, and still haven't really started to build up some
knowledge! One of the projects I should get started on ... too many
loose ends that await some time. Almost set for being QRV on HF.
- Henk, PA8PDP