Intel PXA26X User Manual Page 474

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13-12 Intel® PXA26x Processor Family Developer’s Manual
AC97 Controller Unit
13.4.2.9 Slot 12: I/O Status
The GPIOs configured as inputs return their status on this slot every frame. The data returned on
the latest frame is accessible to software through the codec register at address 0x54 in the modem
codec I/O space. Only the 16 MSBs are used to return GPIO status. Bit 0 in the LSBs indicates a
GPI Input Interrupt event. See the AC97 revision 2.0 spec for more information.
Reads from codec address 0x54 are not transmitted across the link. Data received in slot 12 is
stored internally in the controller and the data from the most recent slot 12 is returned on reads
from address 0x54
13.5 AC-link Low Power Mode
Software must set the GCR[ACLINK_OFF] bit before it enters the processor’s low power modes.
This ensures that the ACUNIT does not drive the output pins on the AC-link.
13.5.1 Powering Down the AC-link
The AC-link signals enter a low power mode when the AC97 codec Powerdown register (0x26) bit
PR4 is set to a 1 (by writing 0x1000). Then the primary codec drives both BITCLK and
SDATA_IN to a logic low voltage level. The sequence follows the timing diagram shown in
Figure 13-7.
The ACUNIT transmits the write to Powerdown register (0x26) over the AC-link. Set up the
ACUNIT so that it does not transmit data to slots 3-12 when it writes to the Powerdown register bit
PR4 (data 0x1000). AC97 revision 2.0 does not require the codec to process other data when it
receives a power down request. When the codec processes the request it immediately transitions
BITCLK and SDATA_IN to a logic low level.
The ACUNIT drives SYNC and SDATA_OUT to a logic low level after programming the
GCR[ACLINK_OFF] to a 1. The ACUNIT maintains nACRESET high when
GCR[ACLINK_OFF]=1.
Figure 13-7. AC-link Powerdown Timing
SDATA
_
OUT
TAG
SYNC
BITCLK
Write to
0x26
Data
PR4
slot 12
prev. frame
TAG
slot 12
prev. frame
SDATA_IN
Note: BITCLK not to scale
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