esp32s3 and pdm mic proof-of-concept

Author: tcsullivan

noisemeter-device/board.h

@@ -28,18 +28,13 @@
 #if defined(BOARD_ESP32_PCB)
 
 /** Pin number for the board's LED. */
-#define PIN_LED1    (0)
-/** Pin number for the board's second LED.
- * @deprecated No longer used; production board only has one LED. */
-#define PIN_LED2    (3)
+#define PIN_LED1    GPIO_NUM_0
 /** Pin number for the board's factory reset button. */
-#define PIN_BUTTON  (1)
-/** Pin number for the microphone's WS pin. */
-#define I2S_WS      (4)
+#define PIN_BUTTON  GPIO_NUM_1
 /** Pin number for the microphone's clock pin. */
-#define I2S_SCK     (5)
+#define I2S_SCK     GPIO_NUM_4
 /** Pin number for the microphone's data out pin. */
-#define I2S_SD      (6)
+#define I2S_SD      GPIO_NUM_5
 
 /** I2S peripheral instance to be used. */
 #define I2S_PORT    I2S_NUM_0
@@ -48,7 +43,7 @@
 #define I2S_FORMAT  I2S_CHANNEL_FMT_ONLY_LEFT
 
 /** Serial instance to use for logging output. */
-#define SERIAL      USBSerial
+#define SERIAL      Serial
 
 #include <HWCDC.h>
 extern HWCDC USBSerial;

noisemeter-device/noisemeter-device.ino

@@ -103,7 +103,7 @@ void setup()
 
   SERIAL.begin(115200);
 
-  if (xTaskCreate(measurementHandler, "dba", 1024, nullptr,
+  if (xTaskCreate(measurementHandler, "dba", 2048, nullptr,
     uxTaskPriorityGet(nullptr), &measurementTask) == pdFAIL)
   {
     SERIAL.println("xTaskCreate failed!");
@@ -245,7 +245,7 @@ void measurementHandler(void *)
 
   while (1) {
     if (const auto db = SPL.readMicrophoneData(); db) {
-      packets.front().add(*db);
+      //packets.front().add(*db);
       printReadingToConsole(*db);
     }
   }

noisemeter-device/spl-meter.cpp

@@ -27,75 +27,71 @@ static constexpr auto SAMPLES_LEQ = SPLMeter::SAMPLE_RATE * LEQ_PERIOD;
 /** Specifies the type of weighting to use for decibel calculation: dBA, dBC, or None/Z. */
 static constexpr auto& WEIGHTING = A_weighting;
 /** Specifies the microphone's equalization filter. See pre-defined filters or set to 'None'. */
-static constexpr auto& MIC_EQUALIZER = SPH0645LM4H_B_RB;
+static constexpr auto& MIC_EQUALIZER = None;
 
 /** Valid number of bits in a received I2S data sample. */
-static constexpr auto MIC_BITS = 24u;
+static constexpr auto MIC_BITS = 16u;
 /** dBFS value expected at MIC_REF_DB (Sensitivity value from datasheet). */
-static constexpr auto MIC_SENSITIVITY = -26.f;
+static constexpr auto MIC_SENSITIVITY = -36.f;
 /** Value at which point sensitivity is specified in datasheet (dB). */
 static constexpr auto MIC_REF_DB = 94.f;
 /** Acoustic overload point (dB). */
-static constexpr auto MIC_OVERLOAD_DB = 120.f;
+static constexpr auto MIC_OVERLOAD_DB = 130.f;
 /** Noise floor (dB). */
-static constexpr auto MIC_NOISE_DB = 29.f;
+static constexpr auto MIC_NOISE_DB = 30.f;
 /** Linear calibration offset to apply to calculated decibel values. */
 static constexpr auto MIC_OFFSET_DB = 0.f;
 
 /** Reference amplitude level for the microphone. */
 static constexpr auto MIC_REF_AMPL = std::pow(10.f, MIC_SENSITIVITY / 20.f) * ((1 << (MIC_BITS - 1)) - 1);
 
-const i2s_config_t SPLMeter::i2s_config = {
-    mode: i2s_mode_t(I2S_MODE_MASTER | I2S_MODE_RX),
-    sample_rate: SAMPLE_RATE,
-    bits_per_sample: i2s_bits_per_sample_t(SPLMeter::SAMPLE_BITS),
-    channel_format: I2S_FORMAT,
-    communication_format: i2s_comm_format_t(I2S_COMM_FORMAT_I2S | I2S_COMM_FORMAT_I2S_MSB),
-    intr_alloc_flags: ESP_INTR_FLAG_LEVEL1,
-    dma_buf_count: 32,
-    dma_buf_len: SPLMeter::SAMPLES_SHORT / 16u,
-    use_apll: true,
-    tx_desc_auto_clear: false,
-    fixed_mclk: 0,
-    mclk_multiple: I2S_MCLK_MULTIPLE_DEFAULT,
-    bits_per_chan: I2S_BITS_PER_CHAN_DEFAULT,
-};
-
-const i2s_pin_config_t SPLMeter::pin_config = {
-    mck_io_num: -1, // not used
-    bck_io_num: I2S_SCK,
-    ws_io_num: I2S_WS,
-    data_out_num: -1,  // not used
-    data_in_num: I2S_SD
-};
-
-constexpr std::int32_t SPLMeter::micConvert(std::int32_t s)
-{
-    return s >> (SAMPLE_BITS - MIC_BITS);
-}
-
 void SPLMeter::initMicrophone() noexcept
 {
-  i2s_driver_install(I2S_PORT, &i2s_config, 0, NULL);
-  i2s_set_pin(I2S_PORT, &pin_config);
-
-  // Discard first block, microphone may need time to startup and settle.
-  i2sRead();
+    i2s_chan_handle_t rx_chan;
+
+    /* Setp 1: Determine the I2S channel configuration and allocate RX channel only
+     * The default configuration can be generated by the helper macro,
+     * but note that PDM channel can only be registered on I2S_NUM_0 */
+    i2s_chan_config_t rx_chan_cfg = I2S_CHANNEL_DEFAULT_CONFIG(I2S_PORT, I2S_ROLE_MASTER);
+    ESP_ERROR_CHECK(i2s_new_channel(&rx_chan_cfg, nullptr, &rx_chan));
+
+    /* Step 2: Setting the configurations of PDM RX mode and initialize the RX channel
+     * The slot configuration and clock configuration can be generated by the macros
+     * These two helper macros is defined in 'i2s_pdm.h' which can only be used in PDM RX mode.
+     * They can help to specify the slot and clock configurations for initialization or re-configuring */
+    i2s_pdm_rx_config_t pdm_rx_cfg = {
+        .clk_cfg = I2S_PDM_RX_CLK_DEFAULT_CONFIG(SAMPLE_RATE),
+        /* The data bit-width of PDM mode is fixed to 16 */
+        .slot_cfg = I2S_PDM_RX_SLOT_PCM_FMT_DEFAULT_CONFIG(I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_MONO),
+        .gpio_cfg = {
+            .clk = I2S_SCK,
+            .din = I2S_SD,
+            .invert_flags = { .clk_inv = false, },
+        },
+    };
+
+    ESP_ERROR_CHECK(i2s_channel_init_pdm_rx_mode(rx_chan, &pdm_rx_cfg));
+
+    /* Step 3: Enable the rx channels before reading data */
+    ESP_ERROR_CHECK(i2s_channel_enable(rx_chan));
+    i2s_handle = rx_chan;
 }
 
 std::optional<float> SPLMeter::readMicrophoneData() noexcept
 {
   i2sRead();
 
-  // Convert (including shifting) integer microphone values to floats,
-  // using the same buffer (assumed sample size is same as size of float),
-  // to save a bit of memory
-  for (auto& s : samples)
-      s.f = micConvert(s.i);
+  // I2S samples are 16-bit integers stored into samples's memory.
+  // These need to be expanded into 32-bit floats for processing.
+  // Iterate in reverse to avoid overwriting data.
+  auto src = reinterpret_cast<const int16_t *>(samples.data()) + samples.size();
+  auto dst = samples.data() + samples.size();
+  for (int i = 0; i < samples.size(); i++)
+      *--dst = *--src;
 
   // Apply equalization and calculate Z-weighted sum of squares,
   // writes filtered samples back to the same buffer.
-  auto fptr = &samples[0].f;
+  const auto fptr = samples.data();
   const auto sum_sqr_SPL = MIC_EQUALIZER.filter(fptr, fptr, samples.size());
 
   // Apply weighting and calucate weigthed sum of squares
@@ -134,7 +130,8 @@ void SPLMeter::i2sRead() noexcept
   //
   // Data is moved from DMA buffers to our 'samples' buffer by the driver ISR
   // and when there is requested ammount of data, task is unblocked
-  size_t bytes_read;
-  i2s_read(I2S_PORT, samples.data(), samples.size() * sizeof(samples[0]), &bytes_read, portMAX_DELAY);
+  size_t bread;
+  (void)bread;
+  i2s_channel_read(i2s_handle, samples.data(), samples.size() * sizeof(int16_t), &bread, portMAX_DELAY);
 }
 

noisemeter-device/spl-meter.h

@@ -21,7 +21,7 @@
 
 #include <array>
 #include <cstdint>
-#include <driver/i2s.h>
+#include <driver/i2s_pdm.h>
 #include <optional>
 
 /**
@@ -43,49 +43,22 @@ class SPLMeter
     std::optional<float> readMicrophoneData() noexcept;
 
 private:
-    /**
-     * During processing, microphone samples can either be ints or floats.
-     * Since sample data takes up a lot of memory, a union is used to reuse
-     * the buffer during processing.
-     */
-    union sample_t {
-        /** Raw integer reading from the microphone. */
-        std::int32_t i;
-        /** Floating-point microphone value created during processing. */
-        float f;
-    };
-    // Both types must be the same size to allow for buffer reuse.
-    static_assert(sizeof(float) == sizeof(std::int32_t));
-
-    /** The number of bits in a single microphone sample. */
-    static constexpr auto SAMPLE_BITS = sizeof(sample_t) * 8u;
     /** The number of samples to keep in the sample buffer. */
     static constexpr auto SAMPLES_SHORT = SAMPLE_RATE / 8u;
-    /** I2S peripheral config. */
-    static const i2s_config_t i2s_config;
-    /** I2S peripheral pin config. */
-    static const i2s_pin_config_t pin_config;
 
     /** Buffer to store microphone samples in for reading and processing. */
     alignas(4)
-    std::array<sample_t, SAMPLES_SHORT> samples;
+    std::array<float, SAMPLES_SHORT> samples;
 
     /** Number of samples included in Leq_sum_sqr accumulation. */
     unsigned Leq_samples = 0;
     /** Accumulation of sums of squares for decibel calculation. */
     float Leq_sum_sqr = 0;
 
+    i2s_chan_handle_t i2s_handle;
+
     /** Reads enough samples from the microphone to fill the samples buffer. */
     void i2sRead() noexcept;
-
-    /**
-     * Converts a raw microphone sample into a usable number.
-     * This is primarily a bit shift to discard unused bits in the left-aligned
-     * 32-bit raw sample.
-     * @param s Sample value to convert
-     * @return Converted sample value ready for processing
-     */
-    static constexpr std::int32_t micConvert(std::int32_t s);
 };
 
 #endif // SPL_METER_H

platformio.ini

@@ -26,8 +26,9 @@ build_unflags =
 build_flags = 
 	-std=gnu++17
 	-DNO_GLOBAL_EEPROM
-        -DNOISEMETER_VERSION=\"0.2.4\"
+        -DNOISEMETER_VERSION=\"0.3.0\"
 	-Wall -Wextra
+	-DUPLOAD_DISABLED
 
 # Optional build flags:
 #   Print credentials over serial (for debugging):
@@ -38,10 +39,9 @@ build_flags =
 #     -DUPLOAD_DISABLED
 
 [env:esp32-pcb]
-board = esp32-c3-devkitm-1
+extra_scripts = build_hooks.py
+board = seeed_xiao_esp32s3
 board_build.f_cpu = 80000000L
-board_build.f_flash = 80000000L
-board_build.flash_mode = qio
 build_flags = ${env.build_flags} -DBOARD_ESP32_PCB
 
 [env:esp32-breadboard]