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13-10 Intel® PXA255 Processor Developer’s Manual
AC’97 Controller Unit
CODEC Ready, sent by the CODEC on its data out stream in bit 15 of Slot 0, is not expected to
change during normal operation. The AC’97 Specification revision 2.0 requires that a CODEC
only change its CODEC Ready status in response to a power down (PR) state change issued by the
ACUNIT. The ACUNIT’s hardware by itself does not monitor the CODEC Ready for the purpose
of sending or receiving data. The ACUNIT stores CODEC Ready in the PCR bit of the GSR for a
primary CODEC and SCR bit of the GSR for a secondary CODEC. Software should monitor PCR
or SCR to trigger a DMA or a programmed I/O operation. The ACUNIT only samples CODEC
Ready valid once and then ignores it for subsequent frames. CODEC Ready is only resampled after
a PR state change.
13.4.2.2 Slot 1: Status Address Port/SLOTREQ bits
Slot 1 is the Status Address Port. Slot 1 monitors the status of ACUNIT functions including, but
not limited to, mixer settings and power management.
Slot 1 echoes the control register index for the data to be returned in Slot 2, if the ACUNIT tags
Slot 1 and Slot 2 as valid during Slot 0.
The ACUNIT only accepts status data (Slot 2 of incoming stream) if the accompanying control
register index (Slot 1 of incoming stream) matches the last valid control register index that was sent
in Slot 1 of the outgoing stream of the most recent previous frame.
For multiple sample rate output, the CODEC examines its sample-rate control registers, its FIFOs’
states, and the incoming SDATA_OUT tag bits at the beginning of each audio output frame to
determine which SLOTREQ bits to set active (low). SLOTREQ bits asserted during the current
audio input frame indicate which output slots require data from the ACUNIT in the next audio
output frame. For fixed 48 kHz operation, the SLOTREQ bits are set active (low), and a sample is
transferred during each frame.
For multiple sample-rate input, the tag bit for each input slot indicates whether valid data is
present.
Again, Slot 1 delivers a CODEC control register index and multiple “sample-rate slot request
flags” for all output slots. AC’97 defines the ten least significant bits of Slot 1 as CODEC on-
demand data request flags for outgoing stream Slots 3-12. For two-channel audio, only data-
request flags corresponding to slots 3 and 4 are meaningful.
Table 13-5. Input Slot 1 Bit Definitions (Sheet 1 of 2)
Bit Description
19 reserved (Filled with zero)
18-12 Control register Index (Filled with zeroes if AC’97 tags it invalid)
11 Slot 3 request: PCM Left channel
10 Slot 4 request: PCM Right channel
9 Slot 5 request: Modem Line 1
8 Slot 6 request: NA
7 Slot 7 request: NA
6 Slot 8 request: NA
5 Slot 9 request: NA