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Reduce memory allocation by one pass combining interleaved steoreo ->… #3105

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Merged
beastoin merged 1 commit into from
Oct 4, 2025
Merged

Reduce memory allocation by one pass combining interleaved steoreo ->… #3105

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64 changes: 20 additions & 44 deletions omi/firmware/omi/src/mic.c
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Original file line number Diff line number Diff line change
Expand Up @@ -39,28 +39,23 @@ static const struct device *dmic_dev;
static volatile mix_handler callback_func = NULL;
static volatile bool mic_running = false;

static inline void
deinterleave_stereo(const int16_t *restrict interleaved, size_t frames, int16_t *restrict left, int16_t *restrict right)
{
/* interleaved: L0, R0, L1, R1, ... */
for (size_t i = 0, j = 0; i < frames; ++i, j += 2) {
left[i] = interleaved[j + 0];
right[i] = interleaved[j + 1];
}
}
#define MAX_FRAMES (MAX_SAMPLE_RATE / 10)
static int16_t mono_buffer[MAX_FRAMES];

static inline void
mixdown_to_mono(const int16_t *restrict left, const int16_t *restrict right, size_t frames, int16_t *restrict mono_out)
interleaved_stereo_to_mono(const int16_t *restrict interleaved, size_t frames, int16_t *restrict mono_out)
{
/* simple 0.5*(L+R) with saturation */
for (size_t i = 0; i < frames; ++i) {
int32_t s = (int32_t) left[i] + (int32_t) right[i];
s >>= 1; /* divide by 2 to avoid clipping */
if (s > 32767)
s = 32767;
if (s < -32768)
s = -32768;
mono_out[i] = (int16_t) s;
/* Mix L and R channels directly from interleaved format: L0, R0, L1, R1, ... */
for (size_t i = 0, j = 0; i < frames; ++i, j += 2) {
int32_t left = (int32_t) interleaved[j + 0];
int32_t right = (int32_t) interleaved[j + 1];
int32_t sum = left + right;
sum >>= 1; /* divide by 2 to avoid clipping */
if (sum > 32767)
sum = 32767;
if (sum < -32768)
sum = -32768;
mono_out[i] = (int16_t) sum;
}
}

Expand All @@ -71,38 +66,19 @@ static void process_audio_buffer(void *buffer, uint32_t size)
size_t frames = size / (BYTES_PER_SAMPLE * CHANNELS);
int16_t *inter = (int16_t *) buffer;

/* Allocate contiguous L and R */
int16_t *left = k_malloc(frames * BYTES_PER_SAMPLE);
int16_t *right = k_malloc(frames * BYTES_PER_SAMPLE);

if (!left || !right) {
LOG_ERR("Out of memory for deinterleave (frames=%zu)", frames);
if (left)
k_free(left);
if (right)
k_free(right);
/* Still free original slab block */
/* Verify we don't exceed static buffer size */
if (frames > MAX_FRAMES) {
LOG_ERR("Frame count %zu exceeds MAX_FRAMES %d", frames, MAX_FRAMES);
k_mem_slab_free(&mem_slab, buffer);
return;
}

deinterleave_stereo(inter, frames, left, right);
interleaved_stereo_to_mono(inter, frames, mono_buffer);

/* Mix to mono and call mono callback */
int16_t *mono = k_malloc(frames * BYTES_PER_SAMPLE);
if (!mono) {
LOG_ERR("Out of memory for mono mix (frames=%zu)", frames);
} else {
mixdown_to_mono(left, right, frames, mono);
if (callback_func) {
callback_func((int16_t *) mono);
}
k_free(mono);
if (callback_func) {
callback_func(mono_buffer);
}

/* Clean up */
k_free(left);
k_free(right);
k_mem_slab_free(&mem_slab, buffer);
}

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