Audio Codec '97

AC ‘97 Component Specification Revision 2.3 Rev 1.0
66
Bit Default Function
G4 Codec
default
Gain Sign Bit
The codec updates this bit with the sign of the gain value present in G[3:0].
The BIOS updates this to take into consideration external amplifiers or other
external logic when relevant.
G[4:0] Codec
default
Gain bits
The codec updates these bits with the gain value (dB relative to level-out) in
1.5dBV increments. The BIOS updates these to take into consideration
external amplifiers or other external logic when relevant.
G[3:0] indicates the magnitude of the gain. G[4] indicates whether the value is
a gain or attenuation.
G[4:0] Gain or Attenuation (dB relative to level-out)
00000 0 dBV
00001 1.5 dBV
01111 24 dBV
10001 -1.5 dBV
11111 -24 dBV
These bits are read/write
INV Codec
default
Inversion bit
Indicates that the codec presents a 180 degree phase shift to the signal.
0h – No inversion reported
1h – Inverted
The Inv bit is Read/Write.
DL[4:0] Codec
default
Buffer delays:
Codec will provide number a value that represents the delay measurement for
the input and output channels. Software will use this value to accurately
calculate audio stream position with respect to what is been reproduced or
recorded.
These values are in 20.83 microsecond (1/48000 second) units.
For output channels, this timing is from the end of AC Link frame in which the
sample is provided, until the time the analog signal appears at the output pin.
For input streams, this is from when the analog signal is presented at the pin
until the representative sample is provided on the AC Link. Analog to Analog
paths are not considered in this measurement.
The measurement is a ‘typical’ measurement, at a 48KHz sample rate, with
minimal in-codec processing (i.e., 3D effects are turned off.)
00h – Information not provided
01h…1Eh – Buffer delay in 20.83
µs units
1Fh – reserved
These bits are R/W. The default value is the delay internal to the codec. The
BIOS may add to this value the known delays external to the codec, such as for
an external amplifier.
IV na Information Valid bit
Indicates whether a sensing method is provided by the codec and if
information field is valid. This field is updated by the codec.
0h – After codec Reset# de-assertion, it indicates the codec does