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It does tickle the DMAC at the start but it seems to just disable it then use PIO to read the floppy boot sector. The read works but the BIOS decides it failed and tries to load ROM BASIC which is missing.

That's weird. How does it decide it failed?

Dunno, it returns 0x20 which according the interrupt list is "controller failure".

Edit: It looks to have some non-standard use for bit 7 of the dor. It reads one sector then toggles that bit. It then looks for the FDC to be waiting for data (rather than sending it).

Edit: I bet bit 7 sets the tc line.

After further review, rather than skipping every other cylinder, like I put in the commit, it looks to be treating the disk as having one side but double the number of cylinders. By that I mean when it wants to read cylinder 0 head 1 the BIOS tells the FDC it wants cylinder 1 head 0 or for cylinder 5 head 1 it asks for cylinder 11 head 0 and so on. I'm not sure of the cleanest way to emulate that.

Maybe it's designed for single-sided 80-track drives -- these did exist 'over here'.

Conveniently, Curt just added a single side quad density drive type.
Using that I get this:

A look in the frame buffer shows DOS is running, it's missing the font.

It's probably located at offset 0, like in mc1502.

The cga font rom region is empty so I borrowed one from IBM.

I did find some glyphs in the f4000 rom.

An unusual layout though.


Edit: found the rest

That's 'primary' encoding defined by GOST 19768-87 -- http://ru.wikipedia.org/wiki/%D0%9E%D1%81%D0%BD%D0%BE%D0%B2%D0%BD%D0%B0%D1%8F_%D0%BA%D0%BE%D0%B4%D0%B8%D1%80%D0%BE%D0%B2%D0%BA%D0%B0

It was sufficiently unpopular that most everyone used 'alternative' encoding (now known as CP866).

An owner of this machine confirmed that is has no DMAC. More dumps surfaced, I'll check them for dups & submit.

Also, with a bit of hackery, I got poisk1 to display something (wrong resolution, though). There's still a lot work to do (hook up the keyboard, at least):