AT2004
4 Channels ADPCM Processor with Echo Cancellation and Conferencing
Page 10 of 25
©2001 Atelic System, Inc
Default: 1 for channel 0, 1, 2, 3;
0 for channel 4, 5, 6, 7.
Rate
Description
0
0
16k ADPCM bitrate
0
1
24k ADPCM bitrate
1
0
32k ADPCM bitrate
1
1
40k ADPCM bitrate
Default: 10 for 32k ADPCM bit-rate
By default, 8 half-channels are specified. The first 4 half-channels are configured as ADPCM decode and the second 4 half-channels are
configured as ADPCM encode.
“Delay” specifies the echo delay in unit of ms. A nonzero “delay” means AT2004 will allocate system resource to this channel to perform
echo cancellation. All nonzero “delay” should be at least 8ms and be an even number.
Per Channel Control Command Sequence
The Per Channel Control command sequence allows the user to specify lots of parameters for each half channel. The command sequence
length is variable, and is dependent on the number of channels that are specified. The format of the command consists of a header, a begin
channel number byte, and a data portion containing information of each channel. The total number of bytes in the command sequence
will be 2+2N where N = number of half channels specified.
Below is a sample of Per Channel Control command sequence for two half channels.
Note: The format of each data fields like channel bypass, stepsize2, stepsize1, comfort noise2, comfort noise1, dc_rmv, NLP_flag, freeze,
EC bypass, tone_flag, EC reset, ADPCM reset, ADPCM bypass, lawA, lawP and idle, are specified below.
Channel
bypass
Description
0
Normal operation
1
Totally bypass, output is same as input
Default: 0
When channel bypass bit is set, the output of the channel will be derived directly from the input instead of from normal operation’s
output. Note that the normal operation of the channel is still performed according to the programmed operation for each individual
function in the channel.
Command Byte [7:0]
Description
0
0
1
1
0
0
A1
A0
Per Channel Control
command Header with A1,
A0 chip ID
Channel Configuration Begin
To begin on first channel, set
to 0
High
Byte
Channel
Bypass
Stepsize2
Stepzise1
Comfort
Noise2
Comfort
Noise1
Dc_rmv
NLP_flag
Freeze
Ch0
Low
Byte
EC
bypass
Tone_flag
EC
Reset
ADPCM
Reset
ADPCM
Bypass
LawA
LawP
Idle
Configuration for channel 0
High
Byte
Channel
Bypass
Stepsize2
Stepzise1
Comfort
Noise2
Comfort
Noise1
Dc_rmv
NLP_flag
Freeze
Ch1
Low
Byte
EC
bypass
Tone_flag
EC
Reset
ADPCM
Reset
ADPCM
Bypass
LawA
LawP
Idle
Configuration for channel 1
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