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ADAU 1761 : sudden sampling frequency shift in function of Y memory allocation

Hi

Attached are 2 simple project files containing a 1kHz generator, and an adaptive filter with 712 coeffs  (that isn,t doing anythin) .

179 Mips out of 1024 are used

734 words out of 4096 words X Mem are used

766 words out of 1024 words Y mem are used

Fs = 48 kHz; I measure a bitclock of 3.125 MHz, a Mclk of 12.8 MHz and a Wordselect clock of 48 kHz at the pins of the EVAL board

The 1kHz is available at the output, so working fine.

I increase the length of the adaptive filter to 720 coeffs; still doing nothing:

179 Mips out of 1024 are used

742 words out of 4096 words X Mem are used

774 words out of 1024 words Y mem are used

Fs = 48 kHz; I measure a bitclock of 3.125 MHwx, a Mclk of 12.8 MHz and a Wordselect clock of 48 kHz at the pins of the EVAL board

BUT , Result is now that the output 500 Hz is measured ! It seems that the DSP is running at 24 kHz iso 48 kHz. But clocks are identical.

When I increase the DSP sampling rate in the DSP REgister to 96 kHz, I get 750 Hz... impossible to explain this

Apparently something has changed in the DSP sampling rate  but I can,t find any indication .

I don,t see it neither in the compiled .h files.

It has nothing to do with the adaptive filter itself, just a function that uses more than 766 Y mem words triggers the fault.

Can anyone help ?

Best regards

Stefan Willems

Metis Acoustics

stefan@metisacoustics.be

Best regards

Stefan