CS4281 Programming Manual
DS308PRM1
205
Confidential Draft
3/7/00
22. AC ‘97 INTERFACE
The dual codec architecture of AC ‘97 revision 2.1
is supported, wherein the second codec uses the
same pins from the primary, with the exception of
a separate serial data in line. The
ASDIN/ASDIN2
AC-Link pins is powered from
VAUX
to insure
wakeup capability when Core and PCI power are
removed. The serial port engine is enabled and
running when
SSPM.ACLEN
is set. When
SSPM.ACLEN
is clear, the serial port engine is reset,
powered down, and all serial port registers reset to
their default states. All registers are also reset by
the PCI
RST#
signal except as noted in the register
description (as in SPMC).
22.1
Hardware Architecture
The following pins are used by the AC ‘97/98
serial port.
• ABITCLK
• ASYNC
• ASDOUT
• ASDIN
• ASDIN2/GPIO1
• ARST#
If the system supports only one AC ‘97 codec, the
ASDIN2/GPIO1
pin has extended GPIO
functionality similarity to the GPIO functionality
in the Audio Codec ‘97 spec, revision 2.1. Other
pins with extended functionality include
GPIO3
,
VOLUP
, and
VOLDN
.
VOLUP
and
VOLDN
can only
be programmed as inputs. More information can
be found in the General Purpose Input/Output
Pins section.
22.1.1
AC ‘97 Register Management
The AC ‘97 codec registers are accessed through
slots 0, 1, and 2. Slot 0 contains tag bits for each
slot. Since the interface operates at a constant
48 kHz rate, register updates can occur faster than
they can be sent down the AC-Link. Host software
accesses the Codec registers by setting up the
address (ACCAD) and data (ACCDA) and
selecting the particular codec (
ACCTL.TC
). Then
host software sets the
ACCTL.DCV
bit. Once
DCV
is
set, state machine waits for the next available
frame, sets the tag bits in slot 0 for slots 1 and 2
valid, copies the address from ACCAD to slot 1,
copies the data from ACCDA to slot 2, and then
automatically clears the
DCV
bit (once the frame is
on its way). For the host to send data, it must
actually check that
ACCTL.DCV
is clear otherwise it
would overwrite the last data. Therefore, the host
has a feedback mechanism to delay updating more
registers.
Table 35 lists the registers needed to configure the
AC-Link and the registers in common when two
codecs are connected. The
SSPM.ACLEN
bit enables
the AC-Link engine,
SPMC.RSTN
releases the
ARST#
signal, and the
ACCTL.ESYN
enables
ASYNC
generation. These three steps should enable the
codec to start AC-Link operation. Since the two
codecs share the same
ASDOUT
line, the
ASDOUT
-
specific registers are common to both codecs.
Codec Register access is supported through the
ACCDA and ACCAD registers with the ACCTL
register enabling the actual transfer. The ACOSV
sets the audio data slot valid bits, sent during slot
0, and cause the AC-Link engine to start
requesting slot IDs from the Sound System
Controller. The final common register supports the
EGPIO bits in slot 12 that are programmed (in the
modem codec) for outputs.
Although the ASDOUT line is shared across the
two codecs, a separate data-in line exists for each
codec. Table 36 lists the registers that are unique
to each codec. Before any operations or data can
be sent to a codec, the codec ready bit,
ACSTSx.CRDY
must be active. Another bit exists in
ACSTSx that indicates if the address and data
slots/registers from the codec contain valid data.
Valid data will remain in these registers until read.
No new data is accepted until the old data is read
by host software. The data received is from
register read requests made across the ASDOUT
D
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