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CS4281 Programming Manual
DS308PRM1
153
Confidential Draft
3/7/00
17. SOUND BLASTER
The Sound Blaster Pro emulation is done in hard-
ware and enabled through the Sound System Con-
trol Register,
SSCR.SB
. When
SSCR.SB
goes from a
0 to a 1, the Sound Blaster engine forces a Sound
Blaster reset, which initializes the state machine
and sets the default mixer values.
The Sound Blaster emulation controller recognizes
accesses to the Sound Blaster trap range. Typically
this range is I/O address 0220h to 022Fh. The ad-
dress and read/write function are interpreted and
mapped to a read/write of the appropriate physical
register. All Sound Blaster I/O registers are
mapped into PCI memory.
Sound Blaster FM functions map directly to the
FM hardware registers. This is a simple address
translation from the I/O trap address to the memory
mapped FM address.
The Sound Blaster DSP is emulated in hardware by
responding to the I/O traps through the IOTSB reg-
ister. The I/O trapping logic maps the I/O locations
to PCI memory mapped space. The controller rec-
ognizes access to the DSP registers and performs
the appropriate function.
Sound Blaster ADPCM is supported by a ADPCM
engine in the DSP controller. Full ADPCM 2:1
(ADPCM4) decompression is supported. The AD-
PCM 3:1 (ADPCM2.6), and 4:1 (ADPCM2) are
decompressed as zeros (no data). Sound Blaster
ADPCM compression is not supported.
When SB playback is enabled, the SRC slot assign-
ments in SRCSA for playback are copied to the slot
assignment bits in the FCRn associated with the
legacy DMAn engine. This forces the playback
SRC to be connected to the proper FIFO. Host soft-
ware must set the Playback SRC mapping to the de-
sired slots, typically 3 and 4. Similarly, when SB
record is enabled, the SRC slot assignments in
SRCSA for record are copied to the same slot as-
signment bits in the FCRn associated with the leg-
acy DMAn. Host software must also set the record
SRC mapping to the desired slots; typically 3 and 4
on the primary AC link. Note that AC-link slot
numbers are encoded with the encoding listed in
Table 37 on page 207. When the SB engine chang-
es from playback to record and vice-versa,
FCRn.FEN
is toggled to flush the legacy FIFOn.
17.1
Sound Blaster Register Addressing
The following table defines the legacy Sound
Blaster I/O address mapping into PCI memory ad-
dress space. The SbBase address is set in I/O Trap
for Sound Blaster (IOTSB).
I/O Address
Description
Type
Address (BA0 Offset)
0
Left FM Status Port
Read
730h
0
Left FM Register Address Port
Write
730h
1
Left FM Data Port
Read/Write
734h
2
Right FM Status Port
Read
738h
2
Right FM Register Address Port
Write
738h
3
Right FM Data Port
Read/Write
73Ch
4
Mixer Register Address
Read/Write
700h
5
Mixer Data Port
Read/Write
704h
6
Reset
Write
708h
8
FM Status Port
Read
730h
8
FM Register Port
Write
730h
9
FM Data Port
Read/Write
734h
A/B
Read Data Port
Read
70Ch
C/D
Command/Write Data
Write
710h
C/D
Write Buffer Status
Read
710h
E/F
Data Available Status
Read
714h
Table 20. Sound Blaster Direct Registers
D
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