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Why Support ADPCM G.726 32k Codec
  
Feb 16, 2007
AR1688 software development is slow. It took us 4 weeks to move from software version 0.06 to 0.07 and still failed to provide a steady iLBC codec support in version 0.07. Instead, we added ADPCM G.726 32k codec support in this version. We have never supported G.726 in PA1688 before because we never think it is important. And we do not think G.726 is important neither with AR1688. The reason we added it, is because we met so many unexpected problem with iLBC, and we have to run something simpler to test the DSP core inside AR1688. With G.711, GSM 6.10, ADPCM G.726 32k and a LMS based echo cancellation algorithm running on AR1688 steadily. We have least found 3 problems related with DSP instructions:
1. af = reg + const instruction will not give correct answer and will not set flag correctly
2. m register can not be set to negative value when used with circle buffer
3. cntr will be pushed immediately on to counter stack instead of waiting for "do" instructions executed, not consistent with standard ADSP21xx
Hopefully, all bad news are over and we can release iLBC support soon. The good news is, most people reporting that AR1688 voice quality is greater than PA1688. And with our internal test, it not only has better quality, it also has less hardware delay and runs more steadily.

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