Hello,
We use a custom board based on DSP TMS320DM642AGNZ (A5, 2003, CC-28C5FFW) and we have an issue in production - around 10-30% of boards do not pass audio quality test. After investigation we discovered that samples are dropped occasionally at a rate around 1-3 samples per 10000 inside of the DSP. For those boards which pass the test the problem is never reproducible.
We have checked signals integrity and everything seems o.k. The DSP temperature has no effect.
We also checked that McASP does not report Frame or EDMA errors.
We found a workaround which seems to be working, but we need your help to understand what is happening. And eventually we have to decide weather we should allow these cards in production.
In our configuration we use McASP to communicate with two codecs AIC23. In further tests we will be using digital loopback at DSP level, so codecs are not required to reproduce the issue.
McASP configuration:
- external clock 12.288MHz is taken from AHCLKX0
- ACLKR0, AHCLKR0,AMUTE,AMUTEIN are not used and not connected
- AFSR0, AFSX0 pins are connected together on the board.
- Master mode, Frame Sync and BCLK are generated by DSP
- TDM mode, 32KHz frame rate, 3072MHz BCLK, 6 time slots from which only 2 are active
- 16 bit sample size
EDMA configuration:
- Four channels are configured to serve two serializers: EDMA_CHA_AXEVTO0, EDMA_CHA_AXEVTE0, EDMA_CHA_AREVTO0, EDMA_CHA_AREVTE0.
- Linking is used to alternate two (ping-pong) buffers for each channel.
- Buffers are located in internal SRAM.
- The interrupt is set for each 512 samples.
We found several case which makes the issue disappear:
- TDM mode, FS 32kHz, 1024MHz BCLK (instead of 3072MHz), 2 time slots
or
- Using internal clock instead of external AHCLKX0 (external signal quality has been certified by our expert).
To help investigate the issue I stripped the production code to make a minimal test application, which you can find in the attachment. It does not depend on any external hardware (except for external clock 12.288MHz on AHCLKX0 pin).
Software tools description
- Code Composer version 3.1.23
- Code Generation Tools 5.1.10
Thank you
Best regards,
Dzmitry