Intel PXA255 - Manual (Page 463)

Intel® PXA255 Processor Developer’s Manual 13-13
AC’97 Controller Unit
The ACUNIT transmits the write to the Powerdown Register (0x26) over the AC-link. Set up the
ACUNIT so that it does not transmit data in Slots 3-12 when it writes 0x1000 to the PR4 bit of the
Powerdown Register. AC’97 revision 2.0 does not require the CODEC to process other data when
it receives a power down request. When the CODEC receives the power down request, it
immediately transitions BITCLK and SDATA_IN to a logic low level.
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 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 one. 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 one microsecond 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 AC’97 wake-up event
(SDATA_IN high for more than one microsecond). When the ACUNIT is ready, it responds to the
wake-up event by asserting a warm or cold reset (see
Figure 13-8 ). 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.
Figure 13-8. SDATA_IN Wake Up Signaling
NOTES:
1. After SDATA_IN goes high, SYNC must be held for a minimum of 1
µ
Sec.
2. The minimum SDATA_IN wake up pulse width is 1
µ
Sec.
3. BITCLK not to scale
B1027-01
TAG
Note 1
Note 2
Notes:
After SDATA_IN goes high, SYNC must be held for a minimum of 1 µSec.
The minimum SDATA_IN wake up pulse width is 1 µSec.
BITCLK not to scale.
slot12
prev.
frame
slot12
prev.
frame
TAG
TAG
TAG Slot
1
Slot
1
Slot
2
Slot
2
Write
to
0x26
Data
FR4
Power Down
Frame
Codec Sleep
State
Wake
Event New Audio
Frame
SYNC
BITCLK
SDATA_OUT
SDATA_IN