This info should help the current snd-sbxfi driver to actually work with the "Vista compatible" cards that it currently does not work with. I believe the true UAA to 20K1 mode switch code is missing from the current alsa snd-sbxfi driver.
PCI BARs
UAA mode, or Vista Compatibility mode. BAR0: 16K for UAA 14h BAR1: 2M for 20k1 (low 32 bit) 18h 2M for 20k1 (high 32 bit) 1Ch BAR2: Between 2 and 256M for 20k1 (low 32 bit) 20h Between 2 and 256M for 20k1 (high 32 bit) 24h BAR3: 32 bit I/O for 20K1
20K1 Mode BAR0: 32 bit I/O for 20K1 14h BAR1: 2M for 20k1 (low 32 bit) 18h 2M for 20k1 (high 32 bit) 1Ch BAR2: Between 2 and 256M for 20k1 (low 32 bit) 20h Between 2 and 256M for 20k1 (high 32 bit) 24h
"UAA/20K1 mode" and "config space selection" work independently of each other.
1) Configuration space selection:
This allows the driver to talk to both the UAA and 20K1 configuration space whichever mode (UAA or 20K1) the card is in. Location: PCI Register 0xA0 for "20K1 Configuration Space Flag" register.
Value: 0x12345678 to select 20K1 without BAR0 exposed; Value: 0x87654321 to select 20K1 with BAR0 exposed; (should disable immediately after using.) Value: 0x00000000 to select UAA.
2) UAA/20K1 MODE CHANGE (controls who the bus master is): The "Mode Change" register is located in the UAA configuration space at location offset 0x3FFC. This location stores 4 values in a ring. To switch from 20K1 mode to UAA mode write each DW value: CTLA, CTLZ, CTLL, CTLA. To switch from UAA mode to 20K1 mode write each DW value: CTLX, CTL-, CTLF, CTLi To read the current mode, the 4 value ring may be in any position, so one might read for example: CTLL, CTLA, CTLA, CTLZ
At power on, the card is in UAA mode. In UAA mode, the UAA chip is the bus master. In 20K1 mode, the 20K1 chip is the bus master. Under either UAA mode or 20K1 mode, the driver can read and write the configuration space of both UAA chip and 20K1 chip.