[Coco] Glenside IDE + Multi-Pak + HDB-DOS

Mark J. Blair nf6x at nf6x.net
Sun Sep 11 17:48:41 EDT 2016

> On Sep 11, 2016, at 14:24, Robert Gault <robert.gault at att.net> wrote:
> The issue with the Glenside controller probably is not caused by the MPI "reflecting" addresses at $FF7x. There looks to be some timing issue, maybe in the HDBDOS code. Boisy mentions READ problems not WRITE ones.

Interesting! I don't understand the MPI in great detail yet, but I have been studying the Glenside IDE schematic today. It appears to me that it makes use of offsets $0..$8 from its base address (either $FF50 or $FF70), and will drive garbage on the D bus for reads at offsets $9..$F. Is the MPI slot select register at $FF7F readable by the CoCo? If so, I can see how the Glenside IDE would at least garble MPI slot select register reads if the Glenside card it jumpered for $FF7x. I'd like to understand the MPI a lot better, including any partial address decoding that might cause unexpected conflicts with other hardware.

Maybe I need to study this possible timing issue more to figure out what is going on. The CF adapter I'm designing would be a new design using a CPLD for all of the logic. I want it to be usable in an MPI, so I would need to address any timing issues whether they lie in the hardware design or the HDB-DOS code.

> While this is not exactly the same as I have a Ken-Ton controller rather than the Glenside IDE, with my MPI system the hard drives are addressed in the $FF7x range with my Disto SCII controller set to the alternate $FF5x range.

It might be because my brain is addled by the cold I'm presently suffering, but I don't think I understand the point you're making there.

I've been contemplating whether I should make a fully Glenside-IDE-compatible CF adapter vs. taking more liberty with the design. I gather that the Glenside IDE fully decodes the address bus rather than using the SCS signal so that it can coexist with a floppy controller on a Y cable. I'm not sure that it makes sense to expect my new widget to be used on a Y cable with a floppy controller, since I plan to include an EEPROM on my widget which would conflict with the ROM in a Y-cabled floppy controller. If I assumed that my widget would never be used on a Y cable, then I could use SCS for the CF card base address, and that might even let me use a smaller and cheaper CPLD since I would not need to decode A15..4. But that would also break compatibility with existing Glenside-aware software, which would at least need to be patched for a different base address at $FF4x. 

Mark J. Blair, NF6X <nf6x at nf6x.net>

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