qtalker---/firmware/esp32p4-sensor-node/test/test_mems_level.c

// MEMS mic RMS -> dBFS tests.
//
// These prove the arithmetic: that a full-scale block reads ~0 dBFS, that
// silence reads the -120 floor rather than -inf or NaN (which would poison
// the JSON payload the backend receives), and that the level rises
// monotonically with amplitude. They prove nothing about whether the
// right-shift-by-8 matches this specific module's real bit alignment —
// that needs a mic.

#include "../main/mems_level.h"
#include "test_util.h"

#include <math.h>
#include <stddef.h>

#define N 256

void test_mems_level(void) {
    SUITE("mems_level");

    // A 24-bit sample sits left-justified in the 32-bit slot, so the raw
    // slot value for full scale is 2^23 << 8.
    const int32_t full_scale_slot = (int32_t)(8388607 << 8); // 2^23 - 1, shifted up

    // --- full scale reads ~0 dBFS ----------------------------------------
    {
        int32_t buf[N];
        for (size_t i = 0; i < N; i++) buf[i] = full_scale_slot;
        double rms = mems_level_rms(buf, N);
        CHECK_NEAR(rms, 8388607.0, 1.0, "full-scale slots recover the 24-bit magnitude");
        double dbfs = mems_level_dbfs(rms);
        CHECK_NEAR(dbfs, 0.0, 0.01, "full-scale input is ~0 dBFS (got %.4f)", dbfs);
        CHECK(dbfs <= 0.0, "dBFS never exceeds 0 for an in-range input");
    }

    // --- silence reads the floor, not -inf or NaN ------------------------
    {
        int32_t buf[N];
        for (size_t i = 0; i < N; i++) buf[i] = 0;
        double rms = mems_level_rms(buf, N);
        CHECK(rms == 0.0, "an all-zero block has zero RMS");
        double dbfs = mems_level_dbfs(rms);
        CHECK(dbfs == MEMS_DBFS_FLOOR, "silence clamps to the -120 floor (got %.4f)", dbfs);
        CHECK(!isinf(dbfs), "silence must not be -inf");
        CHECK(!isnan(dbfs), "silence must not be NaN");

        // Sub-LSB dither in the padding bits still counts as silence
        // because the >>8 discards it.
        int32_t buf2[N];
        for (size_t i = 0; i < N; i++) buf2[i] = (int32_t)(i % 256); // padding bits only
        double dbfs2 = mems_level_dbfs(mems_level_rms(buf2, N));
        CHECK(dbfs2 == MEMS_DBFS_FLOOR, "sub-LSB noise stays at the floor (got %.4f)", dbfs2);
    }

    // --- halving amplitude drops the level by ~6 dB ----------------------
    {
        int32_t loud[N], quiet[N];
        for (size_t i = 0; i < N; i++) {
            loud[i]  = (int32_t)(4194304 << 8); // 2^22, i.e. -6 dBFS
            quiet[i] = (int32_t)(2097152 << 8); // 2^21, i.e. -12 dBFS
        }
        double d_loud  = mems_level_dbfs(mems_level_rms(loud, N));
        double d_quiet = mems_level_dbfs(mems_level_rms(quiet, N));
        CHECK_NEAR(d_loud, -6.0206, 0.001, "2^22 is -6 dBFS (got %.4f)", d_loud);
        CHECK_NEAR(d_quiet, -12.0412, 0.001, "2^21 is -12 dBFS (got %.4f)", d_quiet);
        CHECK_NEAR(d_loud - d_quiet, 6.0206, 0.001, "halving amplitude costs ~6 dB");
    }

    // --- negative samples contribute the same energy as positive ---------
    {
        int32_t pos[N], neg[N], alt[N];
        for (size_t i = 0; i < N; i++) {
            pos[i] = (int32_t)(1000000 << 8);
            neg[i] = (int32_t)(-(1000000 << 8));
            alt[i] = (i % 2) ? (int32_t)(1000000 << 8) : (int32_t)(-(1000000 << 8));
        }
        double rp = mems_level_rms(pos, N);
        double rn = mems_level_rms(neg, N);
        double ra = mems_level_rms(alt, N);
        CHECK_NEAR(rp, 1000000.0, 1.0, "positive DC block RMS");
        CHECK_NEAR(rn, 1000000.0, 1.0, "negative DC block has the same RMS (sign-independent)");
        CHECK_NEAR(ra, 1000000.0, 1.0, "an alternating square wave has the same RMS");
    }

    // --- level rises monotonically with amplitude ------------------------
    {
        double prev = -1000.0;
        for (int shift = 4; shift <= 23; shift++) {
            int32_t buf[N];
            int32_t mag = (int32_t)1 << shift;
            for (size_t i = 0; i < N; i++) buf[i] = mag << 8;
            double dbfs = mems_level_dbfs(mems_level_rms(buf, N));
            CHECK(dbfs > prev, "level rises with amplitude at 2^%d (%.4f <= %.4f)", shift, dbfs, prev);
            CHECK(dbfs >= MEMS_DBFS_FLOOR && dbfs <= 0.0,
                  "level stays inside [%.1f, 0] at 2^%d (got %.4f)", MEMS_DBFS_FLOOR, shift, dbfs);
            CHECK(!isnan(dbfs) && !isinf(dbfs), "level is finite at 2^%d", shift);
            prev = dbfs;
        }
    }

    // --- degenerate inputs ------------------------------------------------
    {
        int32_t buf[1] = { 0 };
        CHECK(mems_level_rms(NULL, 8) == 0.0, "NULL sample buffer yields 0 RMS, not a crash");
        CHECK(mems_level_rms(buf, 0) == 0.0, "an empty block yields 0 RMS, not a divide by zero");
        CHECK(mems_level_dbfs(mems_level_rms(buf, 0)) == MEMS_DBFS_FLOOR,
              "an empty block reports the floor");
    }
}