MY first thought is: if the BIOS and chipset does not support APM then even if the hardware were there... would a mod work ? I would think no.
added: Maybe mkarcher or one of the other super smart guys can shed some light on this approach.

what if an Extension BIOS was written to enable this on the AIB (Add-In Board) and this AIB has it's own dedicated controller for this? Perhaps that would work?

for example, you can build an andruino board that take command from serial port of pc, when you shutdown, you can write your own program that will send command via pc serial port to andruino.
In andruino, when receive that command you can program it to cut off the power to pc by activate/deactivate the relay to the PS_ON pin of PSU (you can power the andruino via 5vsb from psu)
basically you need to implement the circuit to manage the power to the pc

nhattu1986 wrote on 2023-10-11, 04:20:

for example, you can build an andruino board that take command from serial port of pc, when you shutdown, you can write your own program that will send command via pc serial port to andruino.
In andruino, when receive that command you can program it to cut off the power to pc by activate/deactivate the relay to the PS_ON pin of PSU (you can power the andruino via 5vsb from psu)
basically you need to implement the circuit to manage the power to the pc

sounds like an internal serial port card can be made with an open bios of sorts that can tell the arduino to do it's thing as well as be apm compliant. you see, this needs to be an add-on card that just works with existing windows 95 and up apm drivers to interest people. this will also require a soft on power button and a ATX PSU in the case. I was thinking about this being on an isa add-in board with extention bios.

It looks like the APM functions are called by OS through Int15 so it should be possible to get by even with just a TSR and not explicitly need an option ROM or anything.
APM 1.2 spec can be found easily through google, it looks to have all the info necessary to get going.

nice to know but an option ROM seems to be more eligant as it would work on more opperating systems unless of course the opperating system can still access the controller without either of them installed.