Add SPM1423 PDM microphone driver, fix speaker I2S port

Microphone on I2S_NUM_0 (PDM hardware constraint), speaker moved to
I2S_NUM_1. Both init at boot, shut down before deep sleep.
Mic provides raw audio read and RMS level measurement.
Boot beep disabled (speaker confirmed working).

Microphone.h

@@ -0,0 +1,82 @@
+// SPM1423 PDM Microphone Driver — Minimal audio input for T-Watch Ultra
+// PDM input on I2S_NUM_0 (hardware constraint for PDM on ESP32-S3)
+
+#ifndef MICROPHONE_H
+#define MICROPHONE_H
+
+#if BOARD_MODEL == BOARD_TWATCH_ULT
+
+#include "driver/i2s.h"
+
+#define MIC_CLK_PIN   17         // PDM clock (WS pin in I2S terms)
+#define MIC_DAT_PIN   18         // PDM data input
+#define MIC_I2S_PORT  I2S_NUM_0  // PDM only works on I2S0
+#define MIC_SAMPLE_RATE 16000    // 16kHz max for PDM mic
+#define MIC_BUF_SIZE  1024
+
+static bool mic_ready = false;
+
+bool mic_init() {
+  i2s_config_t i2s_config = {};
+  i2s_config.mode = (i2s_mode_t)(I2S_MODE_MASTER | I2S_MODE_RX | I2S_MODE_PDM);
+  i2s_config.sample_rate = MIC_SAMPLE_RATE;
+  i2s_config.bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT;
+  i2s_config.channel_format = I2S_CHANNEL_FMT_ONLY_RIGHT;
+  i2s_config.communication_format = I2S_COMM_FORMAT_STAND_PCM_SHORT;
+  i2s_config.intr_alloc_flags = ESP_INTR_FLAG_LEVEL1;
+  i2s_config.dma_buf_count = 6;
+  i2s_config.dma_buf_len = 512;
+  i2s_config.use_apll = true;
+
+  i2s_pin_config_t pin_config = {};
+  pin_config.bck_io_num = I2S_PIN_NO_CHANGE;
+  pin_config.ws_io_num = MIC_CLK_PIN;
+  pin_config.data_out_num = I2S_PIN_NO_CHANGE;
+  pin_config.data_in_num = MIC_DAT_PIN;
+  pin_config.mck_io_num = I2S_PIN_NO_CHANGE;
+
+  if (i2s_driver_install(MIC_I2S_PORT, &i2s_config, 0, NULL) != ESP_OK) {
+    return false;
+  }
+  if (i2s_set_pin(MIC_I2S_PORT, &pin_config) != ESP_OK) {
+    i2s_driver_uninstall(MIC_I2S_PORT);
+    return false;
+  }
+
+  mic_ready = true;
+  return true;
+}
+
+void mic_end() {
+  if (mic_ready) {
+    i2s_driver_uninstall(MIC_I2S_PORT);
+    mic_ready = false;
+  }
+}
+
+// Read raw audio samples into buffer. Returns bytes read.
+size_t mic_read(int16_t *buf, size_t samples) {
+  if (!mic_ready) return 0;
+  size_t bytes_read = 0;
+  i2s_read(MIC_I2S_PORT, buf, samples * sizeof(int16_t), &bytes_read, portMAX_DELAY);
+  return bytes_read / sizeof(int16_t);
+}
+
+// Get current audio level (RMS of a short sample). Returns 0-32767.
+uint16_t mic_level() {
+  if (!mic_ready) return 0;
+
+  int16_t buf[256];
+  size_t samples = mic_read(buf, 256);
+  if (samples == 0) return 0;
+
+  uint64_t sum_sq = 0;
+  for (size_t i = 0; i < samples; i++) {
+    int32_t s = buf[i];
+    sum_sq += s * s;
+  }
+  return (uint16_t)sqrt((double)sum_sq / samples);
+}
+
+#endif // BOARD_MODEL == BOARD_TWATCH_ULT
+#endif // MICROPHONE_H

RNode_Firmware.ino

@@ -29,8 +29,9 @@
   SensorBHI260AP *bhi260 = NULL;
   bool bhi260_ready = false;
 
-  // MAX98357A I2S speaker
+  // MAX98357A I2S speaker + SPM1423 PDM microphone
   #include "Speaker.h"
+  #include "Microphone.h"
 
   // CST9217 capacitive touch panel
   #include <touch/TouchDrvCST92xx.h>
@@ -307,9 +308,9 @@ void setup() {
         attachInterrupt(TP_INT, touch_isr, FALLING);
       }
 
-      // Init speaker (BLDO2 already enabled by PMU init)
+      // Init speaker (BLDO2 already enabled by PMU init) and microphone
       speaker_init();
-      if (speaker_ready) speaker_beep();  // Boot audio feedback
+      mic_init();
 
       // BHI260AP init deferred — firmware upload takes ~10s at 1MHz I2C
       // and blocks serial communication during boot. Will be initialized
@@ -2078,6 +2079,7 @@ void twatch_enter_deep_sleep(bool beacon_timer) {
   }
 
   // 1. Shut down audio and display before closing buses
+  mic_end();
   speaker_end();
   #if HAS_DISPLAY
     co5300_sleep();

Speaker.h

@@ -12,7 +12,7 @@
 #define SPK_BCLK   I2S_BCLK
 #define SPK_WCLK   I2S_WCLK
 #define SPK_DOUT   I2S_DOUT
-#define SPK_I2S_PORT I2S_NUM_0
+#define SPK_I2S_PORT I2S_NUM_1  // I2S_NUM_0 reserved for PDM microphone
 #define SPK_SAMPLE_RATE 16000
 #define SPK_TONE_BUF_SIZE 512