307013-003 Datasheet, PDF (237/848 Pages) Intel Corporation – Intel I/O Controller Hub 7

Functional Description
Table 5-60. Output Tag Slot 0
Primary
Bit
Access
Example
15
1
14
1
13
1
12:
3
X
2
0
1:0
00
Secondary
Access
Example
1
0
0
X
0
01
Description
Frame Valid
Slot 1 Valid, Command Address bit (Primary codec
only)
Slot 2 Valid, Command Data bit (Primary codec only)
Slot 3–12 Valid
Reserved
Codec ID (00 reserved for primary; 01 indicate
secondary; 10 indicate tertiary)
When accessing the codec registers, only one I/O cycle can be pending across the AC-
link at any time. The ICH7 implements write posting on I/O writes across the AC-link
(i.e., writes across the link are indicated as complete before they are actually sent
across the link). In order to prevent a second I/O write from occurring before the first
one is complete, software must monitor the CAS bit in the Codec Access Semaphore
register which indicates that a codec access is pending. Once the CAS bit is cleared,
then another codec access (read or write) can go through. The exception to this being
reads to offset 54h/D4h/154h (slot 12) which are returned immediately with the most
recently received slot 12 data. Writes to offset 54h, D4h, and 154h (primary, secondary
and tertiary codecs), get transmitted across the AC-link in slots 1 and 2 as a normal
register access. Slot 12 is also updated immediately to reflect the data being written.
The controller does not issue back to back reads. It must get a response to the first
read before issuing a second. In addition, codec reads and writes are only executed
once across the link, and are not repeated.
5.22.3 AC-Link Low Power Mode
The AC-link signals can be placed in a low-power mode. When the AC ’97 Powerdown
register (26h), is programmed to the appropriate value, both ACZ_BIT_CLK and
ACZ_SDIN will be brought to, and held at a logic low voltage level.
Figure 5-15. AC-Link Powerdown Timing
SYNC
BIT_CLK
SDOUT
slot 12
prev. frame
TAG
Write to Data
0x20 PR4
SDIN
slot 12
prev. frame
TAG
Note:
BIT_CLK not to scale
Intel ^® ICH7 Family Datasheet
237