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jeplerjepler
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samd: PDMIn: Reduce code unrolling on samd21 only
Instead of unrolling the code 16 times, unroll it 4 times and loop over it 4 times. This gives the same 16 iterations, but at an expense of less flash space.
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1 file changed

Lines changed: 6 additions & 2 deletions

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  • ports/atmel-samd/common-hal/audiobusio

‎ports/atmel-samd/common-hal/audiobusio/PDMIn.c‎

Lines changed: 6 additions & 2 deletions
Original file line numberDiff line numberDiff line change
@@ -337,7 +337,11 @@ const uint16_t sinc_filter [OVERSAMPLING] = {
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94, 63, 39, 21, 9, 2, 0, 0
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};
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#define REPEAT_16_TIMES(X) X X X X X X X X X X X X X X X X
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#ifdef SAMD21
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#define REPEAT_16_TIMES(X) do { for(uint8_t j=0; j<4; j++) { X X X X } } while (0)
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#else
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#define REPEAT_16_TIMES(X) do { X X X X X X X X X X X X X X X X } while(0)
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#endif
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static uint16_t filter_sample(uint32_t pdm_samples[4]) {
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uint16_t running_sum = 0;
@@ -354,7 +358,7 @@ static uint16_t filter_sample(uint32_t pdm_samples[4]) {
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filter_ptr++;
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pdm_sample <<= 1;
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}
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)
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);
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}
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return running_sum;
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}

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