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4.0 Functional Description
(Continued)
All of the legacy sound blaster mixer register except MX80, MX81 and MX82 are implemented virtually using the opl3 emulation
RAM (512 bytes). Please refer to section 2.3 to get detailed description of the virtual implementation method.
The implemented MX80, MX81 are all read/write registers. Contents of MX80 and MX81 must be consistent with header 1 inter-
rupt line configuration register. MX80 and MX81 can be accessed through AudioBase based port. MX82 is a part of the Audio in-
terrupt status register.
4.2.1.18 Implementation Note For Legacy Sound Blaster Mixer
4.2.1.18.1
To ease our design and maintain the game compatibility on mixer volume set, writing to the legacy sound blaster mixer
register will set a dirty flag, and this flag will inform the software which one of the AC97 mixer should be updated and
then update it using AudioBase based programming port.
When any one of the SBPRO mixer registers (mixer index from 00h–2Fh) has been updated, a SBPRO volume update dirty flag
will be set at Audio Status Register ASR0.
When any one of the SB16 mixer registers (mixer index from 30h–4Fh) has been updated, a SB16 volume update dirty flag will
be set at Audio Status Register ASR0.
Any time when legacy sound blaster mixer is mixer-reset, a mixer soft-reset dirty flag will be set at Audio Status Register ASR0.
All the SB16 / SBPRO mixer register (index from 02h to 4fh) are implemented using part of the opl3 emulation RAM(512bytes).
Any of the unused RAM cell (mixer index above 48h) can be used as the scratch registers for specific purpose and that’s user
defined.
The AC97 internal mixer registers are accessed via another AudioBase based port. (See 4. AC 97)
4.2.1.19 SBPRO Mixer Register
MX00 Mixer Reset
Write only
Any write to this port will reset MX00-MX4f to default value.
SB ESP_Reset() does not affect any of the mixer register.
When this port is written, a SB mixer soft-reset dirty flag will
be set in ASR0.
MX02 Master Volume
Default
808h
Write
Bit 7..4
reserved
Bit 3..0
16 level master volume for left and right channel
Read
Bit 7..4
master volume for left channel
Bit 3..0
master volume for right channel
MX04 Digital Audio Volume
Default 88h
Write
Bit 7..4 16 level left digital audio volume
Bit 3..0 16 level right digital audio volume
Read
Bit 7..4 left digital audio volume
Bit 3..0 right digital audio volume
MX06 Music Volume
Default 88h
Write
Bit 7..4 reserved
Bit 3..0 16 level music volume for left and right channel
Read
Bit 7..4 left music volume
Bit 3..0 right music volume
MX08 CD-Audio Volume
Default 00h
Write
Bit 7..4 reserved
Bit 3..0 16 level CD-Audio volume for left and right channel
Read
Bit 7..4 left CD-Audio volume
Bit 3..0 right CD-Audio volume
MX0A Microphone Volume
Default 00h
Write
Bit 7..3 reserved
Bit 2..0 8 level microphone volume
Read
Bit 7..3 reserved
Bit 2..0 microphone volume
MX0C Digital Audio Input Control
Default 00h
Dummy read/write register
Bit 7,6 reserved
Bit 5
input filter enable
Bit 4
reserved
Bit 3
input filter high/low
Bit 2,1 input source
Bit 0
reserved
Input filter enable and input filter high/low are dummy read/
write bits for SB PRO compatibility.
Input filter enable: 0 - input low-pass filter on, 1 - off
Input filter high/low: 0 - low filter (3.2 kHz low pass), 1 - high
filter (8.8 kHz low pass)
Input source
Bit 2 Bit 1
0
0
Microphone
0
1
CD-Audio
1
0
Microphone
1
1
External Line-In
MX0E Digital Audio Output Control
Default 00h
Bit 7,6
reserved
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