One of my customer found some difficulties when analyze the data of ADAU7002. Below is the description of the issue.
The block diagram of ADAU7002 in our system is as below.
There is two ADAU7002, which convert PDM data from four MEMS microphones
(ADMP522) to TDM data, TLV320ADC3101 is the master of TDM channel, it receive
MCLK, and create BCLK and WCLK for ADAU7002, it also has stereo line in as
well. The TDM data is input to OMAP processor.
There is total 8 slots in TDM channel, 4 MEMS microphones are at slot 1/2/3/4, and 2 line-in are on slot 5/6, slot 7/8 are idle. the WCLK is 32KHz, BCLK is 8.2MHz, and PDM clock is 2.04MHz, they are seems ok from scope.
The current status is, the stereo line-in works well, but 4 MEMS microphone sounds bad. From the spec of ADAU7002, there 32-bit per TDM slot, but only MOST SIGNIFICENT 20-bit are available, but it seems not match with the spec from software analysis of the TDM data, software needs to ignore the most significant 4 bits to get a voice sounds normal.
So do you have more information about the TDM data format of ADAU7002, and any guide to software guys to analyze the TDM data from ADAU7002?
Below is the schematic for your reference:
More information about the issue:
Below is signal capture from scope, seems the most significant 4bit is always high, the value read by software is FB or 7C, it is abnormal from the audio analysis, it will create a very big value that is no meaning for voice.