Audio System + Drivers (#562)

Drivers/pdm-mic-module/include/drivers/pdm_mic.h

@@ -0,0 +1,41 @@
+// SPDX-License-Identifier: Apache-2.0
+#pragma once
+
+#include <stdint.h>
+#include <stdbool.h>
+#include <tactility/error.h>
+#include <tactility/drivers/audio_codec.h>
+
+struct Device;
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+/**
+ * @brief PDM MEMS microphone configuration.
+ *
+ * Covers any PDM mic with no I2C/register interface -- just I2S PDM RX -- e.g. SPM1423.
+ * There is no I2C parent; the device sits standalone in the devicetree and only
+ * references the I2S controller by name. PDM RX is hardware-restricted to I2S
+ * controller 0 on ESP32 targets, so i2s_device must resolve to that controller.
+ */
+struct PdmMicConfig {
+    /** I2S controller device that carries audio data */
+    struct Device* i2s_device;
+    /** Number of PDM mics wired (1 = mono, 2 = stereo) */
+    uint8_t channels;
+    /**
+     * Fixed digital gain multiplier applied to this mic's samples by audio_stream, as an
+     * integer percentage (100 = 1.0x / no boost, 400 = 4.0x). PDM mics have no hardware
+     * gain control, so this is the only way to compensate for a capsule that's quiet at
+     * the ADC's full-scale output. devicetree has no float property type, hence the
+     * percent-scaled integer encoding. M5Stack's own SPM1423 reference firmware uses a
+     * software multiplier of 4 (i.e. 400 here).
+     */
+    uint16_t input_gain_percent;
+};
+
+#ifdef __cplusplus
+}
+#endif