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i2s-tone

Generate a 440 Hz sine tone and play it out on ALP_E1M_I2S0. The minimal demo for <alp/i2s.h>.

Source: examples/i2s-tone/.

board.yaml​

som:
  sku: E1M-AEN701

preset: e1m-evk

cores:
  m55_hp:
    app: ./src
    peripherals: [i2s]

diagnostics:
  log_level: info

Source (abbreviated)​

#include <alp/i2s.h>
#include <alp/e1m_pinout.h>
#include <math.h>

#define SAMPLE_RATE 44100
#define FRAMES      1024

static int16_t pcm[FRAMES * 2];   /* stereo */

int main(void) {
    alp_i2s_t *i2s = alp_i2s_open(&(alp_i2s_config_t){
        .bus_id         = ALP_E1M_I2S0,
        .sample_rate_hz = SAMPLE_RATE,
        .word_bits      = 16,
        .channels       = 2,
        .format         = ALP_I2S_FMT_I2S,
        .direction      = ALP_I2S_DIR_TX,
        .block_frames   = FRAMES,
    });
    if (i2s == NULL) return -1;

    /* open() only configures + allocates the slab; start the clock. */
    if (alp_i2s_start(i2s) != ALP_OK) return -1;

    for (size_t i = 0; i < FRAMES; i++) {
        double t = (double)i / SAMPLE_RATE;
        int16_t s = (int16_t)(sin(2.0 * M_PI * 440.0 * t) * 16384);
        pcm[i*2 + 0] = s;
        pcm[i*2 + 1] = s;
    }

    /* alp_i2s_write takes a BYTE count, not a frame count. */
    for (int loop = 0; loop < 100; loop++) {
        alp_i2s_write(i2s, pcm, sizeof(pcm), UINT32_MAX);
    }

    alp_i2s_stop(i2s);
    alp_i2s_close(i2s);
    return 0;
}

See also​

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