First post, by LSS10999
For a while I've kept the view that AMD motherboards have no legacy audio capabilities at all, as in most cases TSRs can load but programs still cannot detect Sound Blaster. But recently something new regarding the chipsets were discovered.
While discussing about PCIe-to-PCI, PCI-to-ISA related stuffs, Doomn00b discovered something very interesting to look at. Originally I posted some additional stuffs I've found regarding the chipsets there after some checking and testing, I decided to put up a new thread regarding the discoveries.
The AMD 700 series southbridge register reference guide mentioned some chipset registers that would enable to allow legacy audio I/O addresses (MIDI, Adlib, SB/GUS/WSS) to trigger SMI# (see page 171). The same, identical chipset registers are also present in the previous 600 series (page 147). A little further checking of the publicly released AMD tech docs found that the registers are also present in the SP5100 southbridge used on SR5670/SR5690 server motherboards (page 174).
The registers in question are only available up to 700 series. On 800 series the registers were removed (reserved, see page 147). It's likely the 900 series did the same, but the register reference guide for 900 series is yet to be publicly released.
This is just a possibility as I'm yet to understand how it's supposed to work... I don't think there'd be any examples as no known boards of those chipsets ever made use of those triggers (or have implemented the handlers) as far as I know. Given the privilege level of the system management mode, I think the handler might need to reside in a BIOS module.
It seems to enable the possibility to emulate legacy audio through system management mode handlers on those chipsets, similar to the VSA (or see here), using those specialized SMI# triggers. To which extent those registers' usefulness are for getting legacy audio on those chipsets are yet to be known.