Intel® PXA26x Processor Family Developer’s Manual 13-13
AC97 Controller Unit
13.5.2 Waking up the AC-link

13.5.2.1 Wake up triggered by the Codec

To wake up the AC-link a codec drives its SDATA_IN to a logic high level. The rising edge
triggers the resume interrupt if that codec’s resume enable bit is set to a 1. The CPU then wakes up
the codec using the cold or warm reset sequence. The ACUNIT uses a warm reset to wake up the
primary codec. The codec detects a warm reset when SYNC is driven high for a minimum of 1µs
and the BITCLK is absent. The codec must wait until it samples SYNC low before it can start
BITCLK. The codec that signaled the wake event must keep its SDATA_IN high until it detects
that a warm reset has been completed. The codec can then transition its SDATA_IN low.
Figure 13-8 shows the AC-link timing for a wake up triggered by a codec. Because the processor
may need to be awakened, the power management unit detects the AC97 wake-up event
(SDATA_I N high for more than 1µs). When the ACUNIT is ready, it responds to the wake-up
event by asserting a warm or cold reset (see Figure13-8). A modem codec may require the
capacity to wake up the AC-link to report events such as caller-ID and wake-up-on-ring.

13.5.2.2 Wake Up Triggered by the ACUNIT

AC-link protocol provides fo r a cold AC97 reset and a warm AC97 re set. The current power-down
state ultimately dictates which AC97 reset is used. Registers must stay in the same state during all
power-down modes unless a cold AC97 reset is performed. In a cold AC97 reset, the AC97
registers are initialized to their default values.
After a power down, the AC-link must wait for a minimum of four audio frame times after the
frame in which the power down occurred before it can be reactivated by reasserting the SYNC
signal. When AC-link powers up, it indicates readiness through the codec ready bit (input slot 0,
bit 15).
Figure 13-8. SDATA_IN Wake Up Signaling
NOTES:
1. After SDATA_IN goes high, SYNC must be held for a minimum of 1µSec.
2. The minimum SDATA_IN wake up pulse width is 1µSec.
3. BITCLK not to scale
SDATA
_
OU
T
TAG
SYN
C
BITCL
K
Write to
0x26
Data
PR4
slot 12
prev. frame
TAG
slot 12
prev. frame
SDATA
_
I
N
TAG
Slot 1
Slot 2
Power Down
Wake Even
t
Codec Slee
p
Stat e
New Aud io
TAG
Slot 1
Slot 2
No te 1
No te 2