Tool/software: Code Composer Studio
We are have the C5517 EVM board (Spectrum Digital Rev F) . We want to connect a MEMS digital microphone the the C5517 and perform digital filtering. We have found the demo included with the CLS libraries (version 3.08). Following the demo "MEMS Microphone Direct PDM Input via I2S to a C5515 EVM With Software Decimation" we can compile and run the code in 3.08/demos/decimation in debug mode on the board.
HOWEVER, when we dump the audio from memory and convert the memory mapped digGainOutFrame in to audio as a wav file (still using all the code and Matlab in the demo) - it isn't audio. What we found when we tried different tones (1k, 440Hz and also GND as a silent signal each time we dumped the memory we had EXACTLY the identical values in the dig\GainOutf\rame every time the demo was run. It seems to us that the memory was not been written over.
We do not believe it is recording noise, or that the microphone is faulty. Either of those failure modes would result (or I expect it is always going to result) in a different set of values on the digGainOutFrame each time as it is collecting the input and storing it. We have tested the MEMS microphone PDM output on an oscilloscope and it looks like PDM output.
We only get a "new bunch" of values in the digGainOutFrame if the IDE is closed and restarted and the board is reconnected to, so we are thinking that the values may be from random values introduced by memory initialization and that those are not written over by the decimation demo. We cant understand why the demo would not be writting to the memory as we have read and re-read the demo instructions.
If anyone has an idea of what might be happening i would really appreciate some help
