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nrf: i2s: Comment this slightly tricksy code

This commit is contained in:
jepler 2019-09-09 19:25:52 -05:00
parent 82427612d1
commit fe9605a6a3
1 changed files with 7 additions and 1 deletions
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6
ports/nrf/common-hal/audiobusio/I2SOut.c
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@ -167,11 +167,17 @@ stopping: ;
self->sample_data += bytecount; self->sample_data += bytecount;
bytesleft -= bytecount; bytesleft -= bytecount;
} }
// Find the last frame of real audio data and replicate its samples until
// you have 32 bits worth, which is the fundamental unit of nRF I2S DMA
if (self->bytes_per_sample == 1 && self->channel_count == 1) { if (self->bytes_per_sample == 1 && self->channel_count == 1) {
// For 8-bit mono, 4 copies of the final sample are required
self->hold_value = 0x01010101 * *(uint8_t*)(buffer-1); self->hold_value = 0x01010101 * *(uint8_t*)(buffer-1);
} else if (self->bytes_per_sample == 2 && self->channel_count == 2) { } else if (self->bytes_per_sample == 2 && self->channel_count == 2) {
// For 16-bit stereo, 1 copy of the final sample is required
self->hold_value = *(uint32_t*)(buffer-4); self->hold_value = *(uint32_t*)(buffer-4);
} else { } else {
// For 8-bit stereo and 16-bit mono, 2 copies of the final sample are required
self->hold_value = 0x00010001 * *(uint16_t*)(buffer-2); self->hold_value = 0x00010001 * *(uint16_t*)(buffer-2);
} }
} }