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At the moment ec1841 fails system board test (on the tps2214 floppy from softlist) -- it tests that DMA channel 0 counter is increasing and it doesn't.

Apparently this is because BIOS programs PIT first, DMAC second, and then resets DMAC [1]; but DMAC reset does not clear m_u73_q2 and further DMA cycles aren't triggered.

[1] code starting on line 4880 in https://github.com/shattered/retro-bios/blob/master/ec1841/ec1841.lst

That's nice work, as usual. AFAIK the DMAC implementation is still pretty new so it's quite possible you've found an edge case.

ETA: both patches are in trunk now.

ec1841 is somewhat easier to work on since there's a technical manual and BIOS listing (but no schematics).

Speech synthesis card for this machine was finally found, complete with TM and schematics -- this one would be fun to emulate. Not much is known about it, but it's possible that it uses a TMS5100 clone: http://www.155la3.ru/k1803.htm

iskr1030m keyboard uses MCS48's ENT0 CLK opcode, which is unimplemented in MESS -- any special reason why it was left out?

Lack of test cases, I assume.

Most MAME/MESS CPU cores have opcodes implemented on an as-encountered-in-real-software basis. That way you know when you implement an opcode that you have an immediate test case for it.

OK, so I guess I'll have to fix it :-)

Another thing -- I'm thinking of writing a driver for https://en.wikipedia.org/wiki/DVK and it's early revisions were just a SBC connected via serial port to a terminal (ie15). How do I connect two drivers this way?

i86 cpu core doesn't support some of the 8087 instructions (FINIT, FSTCW, ...) and FPU test in ec1841 fails.

It enables output of system clock on T0 pin which would totally kill performance if a callback handler was attached to it. If it's wired to another CPU's clock input, just use the same clock in the machine config.

No FPU in the 8086 currently. A proper implementation would require a bit of work.