fw/drivers/mic: add QEMU microphone driver

jplexer · jplexer · commit 8098801a11da · 2026-04-28T19:17:51.000+02:00
Signed-off-by: Joshua Jun &lt;lets@throw.rocks&gt;
diff --git a/boards/qemu_emery/defconfig b/boards/qemu_emery/defconfig
@@ -41,3 +41,6 @@ CONFIG_TEMPERATURE_STUB=y
 
 CONFIG_CPUMODE=y
 CONFIG_CPUMODE_STUB=y
+
+CONFIG_MIC=y
+CONFIG_MIC_QEMU=y
diff --git a/boards/qemu_flint/defconfig b/boards/qemu_flint/defconfig
@@ -35,3 +35,6 @@ CONFIG_TEMPERATURE_STUB=y
 
 CONFIG_CPUMODE=y
 CONFIG_CPUMODE_STUB=y
+
+CONFIG_MIC=y
+CONFIG_MIC_QEMU=y
diff --git a/boards/qemu_gabbro/defconfig b/boards/qemu_gabbro/defconfig
@@ -38,3 +38,6 @@ CONFIG_TEMPERATURE_STUB=y
 
 CONFIG_CPUMODE=y
 CONFIG_CPUMODE_STUB=y
+
+CONFIG_MIC=y
+CONFIG_MIC_QEMU=y
diff --git a/src/fw/board/boards/board_qemu_emery.c b/src/fw/board/boards/board_qemu_emery.c
@@ -7,6 +7,7 @@
 #include "drivers/uart/qemu.h"
 #include "drivers/qemu/qemu_audio.h"
 #include "drivers/led_controller.h"
+#include "drivers/mic/qemu/mic_definitions.h"
 
 static UARTDeviceState s_dbg_uart_state = {};
 
@@ -80,6 +81,14 @@ static struct AudioDevice AUDIO_DEVICE = {
 };
 AudioDevice *const AUDIO = (AudioDevice *)&AUDIO_DEVICE;
 
+// Microphone (QEMU stub — feeds silence on a timer)
+static MicDeviceState s_mic_state;
+static MicDevice MIC_DEVICE = {
+  .state = &s_mic_state,
+  .channels = 1,
+};
+MicDevice * const MIC = &MIC_DEVICE;
+
 // IRQ handler trampolines
 IRQ_MAP(UART2, uart_irq_handler, DBG_UART);
 IRQ_MAP(UART1, uart_irq_handler, QEMU_UART);
diff --git a/src/fw/board/boards/board_qemu_emery.h b/src/fw/board/boards/board_qemu_emery.h
@@ -9,6 +9,7 @@
 extern UARTDevice * const DBG_UART;
 extern UARTDevice * const QEMU_UART;
 extern DisplayDevice *const DISPLAY;
+extern MicDevice * const MIC;
 extern const BoardConfigActuator BOARD_CONFIG_VIBE;
 extern const BoardConfigPower BOARD_CONFIG_POWER;
 extern const BoardConfig BOARD_CONFIG;
diff --git a/src/fw/board/boards/board_qemu_flint.c b/src/fw/board/boards/board_qemu_flint.c
@@ -6,6 +6,7 @@
 // UART device for debug serial
 #include "drivers/uart/qemu.h"
 #include "drivers/qemu/qemu_audio.h"
+#include "drivers/mic/qemu/mic_definitions.h"
 
 static UARTDeviceState s_dbg_uart_state = {};
 
@@ -78,6 +79,14 @@ static struct AudioDevice AUDIO_DEVICE = {
 };
 AudioDevice *const AUDIO = (AudioDevice *)&AUDIO_DEVICE;
 
+// Microphone (QEMU stub — feeds silence on a timer)
+static MicDeviceState s_mic_state;
+static MicDevice MIC_DEVICE = {
+  .state = &s_mic_state,
+  .channels = 1,
+};
+MicDevice * const MIC = &MIC_DEVICE;
+
 // IRQ handler trampolines
 IRQ_MAP(UART2, uart_irq_handler, DBG_UART);
 IRQ_MAP(UART1, uart_irq_handler, QEMU_UART);
diff --git a/src/fw/board/boards/board_qemu_flint.h b/src/fw/board/boards/board_qemu_flint.h
@@ -9,6 +9,7 @@
 extern UARTDevice * const DBG_UART;
 extern UARTDevice * const QEMU_UART;
 extern DisplayDevice *const DISPLAY;
+extern MicDevice * const MIC;
 extern const BoardConfigActuator BOARD_CONFIG_VIBE;
 extern const BoardConfigPower BOARD_CONFIG_POWER;
 extern const BoardConfig BOARD_CONFIG;
diff --git a/src/fw/board/boards/board_qemu_gabbro.c b/src/fw/board/boards/board_qemu_gabbro.c
@@ -5,6 +5,7 @@
 
 // UART device for debug serial
 #include "drivers/uart/qemu.h"
+#include "drivers/mic/qemu/mic_definitions.h"
 
 static UARTDeviceState s_dbg_uart_state = {};
 
@@ -68,6 +69,14 @@ const BoardConfigButton BOARD_CONFIG_BUTTON = {
   .timer_irqn = TIMER0_IRQn,
 };
 
+// Microphone (QEMU stub — feeds silence on a timer)
+static MicDeviceState s_mic_state;
+static MicDevice MIC_DEVICE = {
+  .state = &s_mic_state,
+  .channels = 1,
+};
+MicDevice * const MIC = &MIC_DEVICE;
+
 // IRQ handler trampolines
 IRQ_MAP(UART2, uart_irq_handler, DBG_UART);
 IRQ_MAP(UART1, uart_irq_handler, QEMU_UART);
diff --git a/src/fw/board/boards/board_qemu_gabbro.h b/src/fw/board/boards/board_qemu_gabbro.h
@@ -9,6 +9,7 @@
 extern UARTDevice * const DBG_UART;
 extern UARTDevice * const QEMU_UART;
 extern DisplayDevice *const DISPLAY;
+extern MicDevice * const MIC;
 extern const BoardConfigActuator BOARD_CONFIG_VIBE;
 extern const BoardConfigPower BOARD_CONFIG_POWER;
 extern const BoardConfig BOARD_CONFIG;
diff --git a/src/fw/drivers/mic/Kconfig b/src/fw/drivers/mic/Kconfig
@@ -28,4 +28,12 @@ config MIC_STM32F4_PDM
     help
       Support for the ST STM32F4 PDM microphone interface.
 
+config MIC_QEMU
+    bool "QEMU stub"
+    help
+      Software-only microphone stub for QEMU. Delivers silence at
+      MIC_SAMPLE_RATE so the voice service can run end-to-end against
+      `pebble transcribe`, which ignores audio frames and replies with
+      a canned transcription on a timer.
+
 endif # MIC
diff --git a/src/fw/drivers/mic/qemu/mic.c b/src/fw/drivers/mic/qemu/mic.c
@@ -0,0 +1,122 @@
+/* SPDX-FileCopyrightText: 2026 Core Devices LLC */
+/* SPDX-License-Identifier: Apache-2.0 */
+
+#include "drivers/mic.h"
+#include "drivers/mic/qemu/mic_definitions.h"
+
+#include "board/board.h"
+#include "console/prompt.h"
+#include "pbl/services/new_timer/new_timer.h"
+#include "system/logging.h"
+#include "system/passert.h"
+
+#include <inttypes.h>
+#include <string.h>
+
+static void prv_timer_cb(void *data) {
+  MicDevice *this = data;
+  MicDeviceState *state = this->state;
+
+  if (!state->is_running || !state->data_handler || !state->audio_buffer) {
+    return;
+  }
+
+  // QEMU has no real microphone — feed the consumer silence at the expected
+  // cadence so the voice service stays in lockstep with `pebble transcribe`.
+  memset(state->audio_buffer, 0, state->audio_buffer_len * sizeof(int16_t));
+  state->data_handler(state->audio_buffer, state->audio_buffer_len, state->handler_context);
+}
+
+void mic_init(MicDevice *this) {
+  PBL_ASSERTN(this);
+  PBL_ASSERTN(this->state);
+
+  MicDeviceState *state = this->state;
+  if (state->is_initialized) {
+    return;
+  }
+
+  state->timer = new_timer_create();
+  PBL_ASSERTN(state->timer != TIMER_INVALID_ID);
+  state->is_initialized = true;
+}
+
+void mic_set_volume(MicDevice *this, uint16_t volume) {
+  // No gain stage to tweak on the QEMU stub.
+}
+
+bool mic_start(MicDevice *this, MicDataHandlerCB data_handler, void *context,
+               int16_t *audio_buffer, size_t audio_buffer_len) {
+  PBL_ASSERTN(this);
+  PBL_ASSERTN(this->state);
+  PBL_ASSERTN(data_handler);
+  PBL_ASSERTN(audio_buffer);
+  PBL_ASSERTN(audio_buffer_len > 0);
+
+  MicDeviceState *state = this->state;
+  PBL_ASSERTN(state->is_initialized);
+
+  if (state->is_running) {
+    return false;
+  }
+
+  state->data_handler = data_handler;
+  state->handler_context = context;
+  state->audio_buffer = audio_buffer;
+  state->audio_buffer_len = audio_buffer_len;
+
+  // Match the wall-clock cadence of a real mic: one buffer's worth of samples
+  // per period at MIC_SAMPLE_RATE. Round up to keep the period >= 1 ms.
+  uint32_t period_ms = (audio_buffer_len * 1000U + MIC_SAMPLE_RATE - 1U) / MIC_SAMPLE_RATE;
+  if (period_ms == 0) {
+    period_ms = 1;
+  }
+  state->period_ms = period_ms;
+  state->is_running = true;
+
+  if (!new_timer_start(state->timer, period_ms, prv_timer_cb, (void *)this,
+                       TIMER_START_FLAG_REPEATING)) {
+    state->is_running = false;
+    return false;
+  }
+
+  PBL_LOG_INFO("QEMU mic stub started (period=%" PRIu32 "ms)", period_ms);
+  return true;
+}
+
+void mic_stop(MicDevice *this) {
+  PBL_ASSERTN(this);
+  PBL_ASSERTN(this->state);
+
+  MicDeviceState *state = this->state;
+  if (!state->is_running) {
+    return;
+  }
+
+  state->is_running = false;
+  new_timer_stop(state->timer);
+  state->data_handler = NULL;
+  state->handler_context = NULL;
+  state->audio_buffer = NULL;
+  state->audio_buffer_len = 0;
+}
+
+bool mic_is_running(MicDevice *this) {
+  PBL_ASSERTN(this);
+  PBL_ASSERTN(this->state);
+  return this->state->is_running;
+}
+
+uint32_t mic_get_channels(MicDevice *this) {
+  PBL_ASSERTN(this);
+  return this->channels ? this->channels : 1;
+}
+
+void command_mic_start(char *timeout_str, char *sample_size_str, char *sample_rate_str,
+                      char *format_str) {
+  prompt_send_response("Microphone console commands not supported on QEMU");
+}
+
+void command_mic_read(void) {
+  prompt_send_response("Microphone read command not supported on QEMU");
+}
diff --git a/src/fw/drivers/mic/qemu/mic_definitions.h b/src/fw/drivers/mic/qemu/mic_definitions.h
@@ -0,0 +1,27 @@
+/* SPDX-FileCopyrightText: 2026 Core Devices LLC */
+/* SPDX-License-Identifier: Apache-2.0 */
+
+#pragma once
+
+#include "drivers/mic.h"
+#include "pbl/services/new_timer/new_timer.h"
+
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+typedef struct {
+  TimerID timer;
+  MicDataHandlerCB data_handler;
+  void *handler_context;
+  int16_t *audio_buffer;
+  size_t audio_buffer_len;
+  uint32_t period_ms;
+  bool is_initialized;
+  bool is_running;
+} MicDeviceState;
+
+typedef const struct MicDevice {
+  MicDeviceState *state;
+  uint32_t channels;
+} MicDevice;
diff --git a/src/fw/drivers/mic/wscript_build b/src/fw/drivers/mic/wscript_build
@@ -28,6 +28,8 @@ elif bld.env.CONFIG_MIC_STM32F4_PDM:
         'driver_pmic',
         'stm32_stdlib',
     ])
+elif bld.env.CONFIG_MIC_QEMU:
+    sources.append('qemu/mic.c')
 
 bld.objects(
     name='driver_mic',
