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Grah! That sounds like it's going to be a pain and a half, but it's doable, since AFAIK the CHD format includes subcode Q data and subcode R-W data... theoretically.

It does if the rip provides them, but those fields can all be trivially synthesized if necessary too. For CDDA what will be important is the audio flag and the track/index/minutes/seconds/frames values.

The chd format does support the subcode channels. There does not seem to be code to return the subcode information during a TOC read.

The TOC has no subcodes. What planet are your CDs from?

Anyway, cdrom_read_subcode() will read the subcode data if it was stored in the rip (which it isn't for any of these CD-i games as far as I can tell). Otherwise it returns garbage. Sorry

Btw, for pce cd support I put in some code which creates subcode based on the location on the disc.

Yep, CD-i Emulator synthesizes them too. It doesn't even use the subcode info if the disc image has it, which it really should

Oops, originally my mistake. I should have termed it "lead-in read" The TOC is recorded in the Q subcode channel of the lead-in area.

This is not the case, sadly. Something else is upsetting the BIOS when the game tries to play a CDDA track. I can tell, because at no point is the BIOS even getting far enough in the CDDA processing to read from offset 0x924...

My current methodology is:

- First, upon a CDDA request, begin processing after either 1/75th of a second or the current time remaining until a CD sector transfer, whichever comes first
- After processing commences due to the callback...
- Calculate the current MSF frame, calculated by taking CDIC_TIME & 0xffff7f00
- Calculate the next MSF frame, by taking CDIC_TIME & 0xffff7f00 and incrementing by BCD 0x00000100.
- Calculate the next MSF frame, rounded to the next second, by taking CDIC_TIME & 0xffff0000 and incrementing by BCD 0x00010000.
- Set CDIC_TIME to be the next MSF frame
- Read a sector's worth of data at CDIC_TIME
- If we're at frame 0, begin playing a second's worth of CDDA audio by just playing it through the "CDDA" audio device in MESS
- If we're also at frame 0, trigger an interrupt
- Set a callback to trigger after 1/75th of a second, to poll the next MSF frame

I can't seem to determine what CDIC register bits should be set or cleared upon CDDA read...

from a quick look, it seems that you're holding the 68k interrupt line for so long it has no chance / time to do anything else while CDDA is playing.

The only interrupt it ever takes is the CDDA related one, and no further processing takes place therefore the game never advances another frame while the CDDA is playing, because Vbl etc. are never taken.

If you hack the 1hz timer, you can get badly distorted music but the game will continue as normal.

As for the correct solution, you're on your own.