djsundog/circuitpython
1
0
Fork 0
Code Issues Pull Requests Packages Projects Releases Wiki Activity

PDMIn: Make last DMA buffer be exactly the right length.

Browse Source
This commit is contained in:
Dan Halbert 2017-12-23 11:56:10 -05:00 committed by Scott Shawcroft
parent 7918714043
commit e44fbca272
1 changed files with 22 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
atmel-samd/common-hal/audiobusio/PDMIn.c
View File

@ -334,7 +334,7 @@ uint32_t common_hal_audiobusio_pdmin_record_to_buffer(audiobusio_pdmin_obj_t* se
buffer = second_buffer;
descriptor = &second_descriptor;
}
// Decimate and filter the last buffer
// Decimate and filter the buffer that was just filled.
uint32_t samples_gathered = descriptor->BTCNT.reg / words_per_sample;
// Don't run off the end of output buffer. Process only as many as needed.
uint32_t samples_to_process = min(remaining_samples_needed, samples_gathered);
@ -352,10 +352,28 @@ uint32_t common_hal_audiobusio_pdmin_record_to_buffer(audiobusio_pdmin_obj_t* se
buffers_processed++;
// We might need fewer than an entire of samples, but we won't try to alter the
// last DMA, which might already be in progress, so we'll just throw away some
// samples at the end.
// Compute how many more samples we need, and if the last buffer is the last
// set of samples needed, adjust the DMA count to only fetch as necessary.
remaining_samples_needed = output_buffer_length - values_output;
if (remaining_samples_needed <= samples_per_buffer*2 &&
remaining_samples_needed > samples_per_buffer) {
// Adjust the DMA settings for the current buffer, which will be processed
// after the other buffer, which is now receiving samples via DMA.
// We don't adjust the DMA in progress, but the one after that.
// Timeline:
// 1. current buffer (already processed)
// 2. alternate buffer (DMA in progress)
// 3. current buffer (last set of samples needed)
// Set up to receive the last set of samples (don't include the alternate buffer, now in use).
uint32_t samples_needed_for_last_buffer = remaining_samples_needed - samples_per_buffer;
descriptor->BTCNT.reg = samples_needed_for_last_buffer * words_per_sample;
descriptor->DSTADDR.reg = ((uint32_t) buffer)
+ samples_needed_for_last_buffer * words_per_sample * sizeof(buffer[0]);
// Break chain to alternate buffer.
descriptor->DESCADDR.reg = 0;
}
}
stop_dma(self);