dump

Firmware/components/backend-esp/CMakeLists.txt

@@ -4,10 +4,10 @@ idf_component_register(
         "src/buttons.cpp"
         "src/buzzer.cpp"
         "src/esp_backend.cpp"
+        "src/event_bus.cpp"
         "src/display.cpp"
         "src/fs_helper.cpp"
         "src/i2c_global.cpp"
-        "src/power_helper.cpp"
         "src/shutdowner.cpp"
         "src/spi_global.cpp"
         INCLUDE_DIRS

Firmware/components/backend-esp/include/cardboy/backend/esp/buttons.hpp

@@ -5,9 +5,11 @@
 #ifndef BUTTONS_HPP
 #define BUTTONS_HPP
 
+#include "cardboy/sdk/event_bus.hpp"
+
+#include <cstdint>
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
-#include <cstdint>
 
 typedef enum {
     BTN_START  = 1 << 1,
@@ -25,16 +27,18 @@ public:
     static Buttons& get();
     void            pooler(); // FIXME:
     uint8_t         get_pressed();
-    void install_isr();
-    void register_listener(TaskHandle_t task);
+    void            install_isr();
+    void            register_listener(TaskHandle_t task);
+    void            setEventBus(cardboy::sdk::IEventBus* bus);
 
-    TaskHandle_t     _pooler_task;
+    TaskHandle_t _pooler_task;
 
 private:
     Buttons();
 
-    volatile uint8_t _current;
-    volatile TaskHandle_t _listener = nullptr;
+    volatile uint8_t         _current;
+    volatile TaskHandle_t    _listener = nullptr;
+    cardboy::sdk::IEventBus* _eventBus = nullptr;
 };
 
 

Firmware/components/backend-esp/include/cardboy/backend/esp/config.hpp

@@ -20,7 +20,7 @@
 #define DISP_WIDTH  cardboy::sdk::kDisplayWidth
 #define DISP_HEIGHT cardboy::sdk::kDisplayHeight
 
-#define BUZZER_PIN GPIO_NUM_25
+#define BUZZER_PIN GPIO_NUM_22
 
 #define PWR_INT  GPIO_NUM_10
 #define PWR_KILL GPIO_NUM_12

Firmware/components/backend-esp/include/cardboy/backend/esp/event_bus.hpp

@@ -0,0 +1,27 @@
+#pragma once
+
+#include <cardboy/sdk/event_bus.hpp>
+
+#include "freertos/FreeRTOS.h"
+#include "freertos/event_groups.h"
+#include "freertos/timers.h"
+
+namespace cardboy::backend::esp {
+
+class EventBus final : public cardboy::sdk::IEventBus {
+public:
+    EventBus();
+    ~EventBus() override;
+
+    void          signal(std::uint32_t bits) override;
+    void          signalFromISR(std::uint32_t bits) override;
+    std::uint32_t wait(std::uint32_t mask, std::uint32_t timeout_ms) override;
+    void          scheduleTimerSignal(std::uint32_t delay_ms) override;
+    void          cancelTimerSignal() override;
+
+private:
+    EventGroupHandle_t group;
+    TimerHandle_t      timer;
+};
+
+} // namespace cardboy::backend::esp

Firmware/components/backend-esp/include/cardboy/backend/esp/i2c_global.hpp

@@ -22,6 +22,7 @@ private:
             .scl_io_num        = I2C_SCL,
             .clk_source        = I2C_CLK_SRC_DEFAULT,
             .glitch_ignore_cnt = 7,
+            .intr_priority     = 2,
             .flags             = {.enable_internal_pullup = true, .allow_pd = true},
     };
     i2c_master_bus_handle_t _bus_handle;

Firmware/components/backend-esp/include/cardboy/backend/esp/power_helper.hpp

@@ -1,30 +0,0 @@
-//
-// Created by Stepan Usatiuk on 03.03.2025.
-//
-
-#ifndef POWER_HELPER_HPP
-#define POWER_HELPER_HPP
-
-#include "freertos/FreeRTOS.h"
-#include "freertos/event_groups.h"
-
-class PowerHelper {
-public:
-    static PowerHelper& get();
-
-    bool       is_slow() const;
-    void       set_slow(bool slow);
-    BaseType_t reset_slow_isr(BaseType_t* xHigherPriorityTaskWoken);
-    void       delay(int slow_ms, int normal_ms);
-
-    void install_isr();
-
-private:
-    PowerHelper();
-
-    bool               _slow = false;
-    EventGroupHandle_t _event_group;
-};
-
-
-#endif // POWER_HELPER_HPP

Firmware/components/backend-esp/include/cardboy/backend/esp_backend.hpp

@@ -2,6 +2,7 @@
 
 #include <cardboy/sdk/display_spec.hpp>
 #include "cardboy/backend/esp/display.hpp"
+#include "cardboy/backend/esp/event_bus.hpp"
 #include "cardboy/sdk/platform.hpp"
 #include "cardboy/sdk/services.hpp"
 
@@ -58,16 +59,17 @@ private:
     class StorageService;
     class RandomService;
     class HighResClockService;
-    class PowerService;
     class FilesystemService;
+    class LoopHooksService;
 
     std::unique_ptr<BuzzerService>       buzzerService;
     std::unique_ptr<BatteryService>      batteryService;
     std::unique_ptr<StorageService>      storageService;
     std::unique_ptr<RandomService>       randomService;
     std::unique_ptr<HighResClockService> highResClockService;
-    std::unique_ptr<PowerService>        powerService;
     std::unique_ptr<FilesystemService>   filesystemService;
+    std::unique_ptr<EventBus>            eventBus;
+    std::unique_ptr<LoopHooksService>    loopHooksService;
 
     cardboy::sdk::Services services{};
 };

Firmware/components/backend-esp/src/bat_mon.cpp

@@ -4,8 +4,6 @@
 
 #include "cardboy/backend/esp/bat_mon.hpp"
 
-#include "cardboy/backend/esp/power_helper.hpp"
-
 #include "freertos/FreeRTOS.h"
 #include "freertos/task.h"
 
@@ -105,7 +103,7 @@ void BatMon::pooler() {
         _charge  = capToMah(ReadRegister(0x05));
         _current = regToCurrent(ReadRegister(0x0B));
         _voltage = regToVoltage(ReadRegister(0x09));
-        PowerHelper::get().delay(10000, 1000);
+        vTaskDelay(pdMS_TO_TICKS(10000));
         if (_voltage < 3.0f) {
             Shutdowner::get().shutdown();
         }

Firmware/components/backend-esp/src/buttons.cpp

@@ -6,7 +6,6 @@
 
 #include <driver/gpio.h>
 #include <esp_err.h>
-#include "cardboy/backend/esp/power_helper.hpp"
 #include <rom/ets_sys.h>
 
 #include "freertos/FreeRTOS.h"
@@ -14,6 +13,7 @@
 
 #include "cardboy/backend/esp/config.hpp"
 #include "cardboy/backend/esp/i2c_global.hpp"
+#include "cardboy/sdk/event_bus.hpp"
 
 static i2c_master_dev_handle_t    dev_handle;
 static inline i2c_device_config_t dev_cfg = {
@@ -37,12 +37,10 @@ static void wakeup(void* arg) {
         ESP_ERROR_CHECK(gpio_wakeup_enable(EXP_INT, GPIO_INTR_HIGH_LEVEL));
         is_on_low = false;
 
-        BaseType_t xResult                  = pdFAIL;
         BaseType_t xHigherPriorityTaskWoken = pdFALSE;
 
         xTaskNotifyFromISR(Buttons::get()._pooler_task, 0, eNoAction, &xHigherPriorityTaskWoken);
 
-        PowerHelper::get().reset_slow_isr(&xHigherPriorityTaskWoken);
         portYIELD_FROM_ISR(xHigherPriorityTaskWoken);
     } else {
         ESP_ERROR_CHECK(gpio_set_intr_type(EXP_INT, GPIO_INTR_LOW_LEVEL));
@@ -92,9 +90,13 @@ void Buttons::pooler() {
                 i2c_master_transmit_receive(dev_handle, &reg, sizeof(reg), reinterpret_cast<uint8_t*>(&buffer), 1, -1));
         if (_listener)
             xTaskNotifyGive(_listener);
+        if (_eventBus)
+            _eventBus->signal(cardboy::sdk::to_event_bits(cardboy::sdk::EventBusSignal::Input));
     }
 }
 uint8_t Buttons::get_pressed() { return _current; }
 void    Buttons::install_isr() { gpio_isr_handler_add(EXP_INT, wakeup, nullptr); }
 
 void Buttons::register_listener(TaskHandle_t task) { _listener = task; }
+
+void Buttons::setEventBus(cardboy::sdk::IEventBus* bus) { _eventBus = bus; }

Firmware/components/backend-esp/src/esp_backend.cpp

@@ -7,7 +7,6 @@
 #include "cardboy/backend/esp/display.hpp"
 #include "cardboy/backend/esp/fs_helper.hpp"
 #include "cardboy/backend/esp/i2c_global.hpp"
-#include "cardboy/backend/esp/power_helper.hpp"
 #include "cardboy/backend/esp/shutdowner.hpp"
 #include "cardboy/backend/esp/spi_global.hpp"
 
@@ -112,12 +111,6 @@ public:
     [[nodiscard]] std::uint64_t micros() override { return static_cast<std::uint64_t>(esp_timer_get_time()); }
 };
 
-class EspRuntime::PowerService final : public cardboy::sdk::IPowerManager {
-public:
-    void               setSlowMode(bool enable) override { PowerHelper::get().set_slow(enable); }
-    [[nodiscard]] bool isSlowMode() const override { return PowerHelper::get().is_slow(); }
-};
-
 class EspRuntime::FilesystemService final : public cardboy::sdk::IFilesystem {
 public:
     bool                      mount() override { return FsHelper::get().mount() == ESP_OK; }
@@ -128,6 +121,11 @@ public:
     }
 };
 
+class EspRuntime::LoopHooksService final : public cardboy::sdk::ILoopHooks {
+public:
+    void onLoopIteration() override { vTaskDelay(1); }
+};
+
 EspRuntime::EspRuntime() : framebuffer(), input(), clock() {
     initializeHardware();
 
@@ -136,16 +134,20 @@ EspRuntime::EspRuntime() : framebuffer(), input(), clock() {
     storageService      = std::make_unique<StorageService>();
     randomService       = std::make_unique<RandomService>();
     highResClockService = std::make_unique<HighResClockService>();
-    powerService        = std::make_unique<PowerService>();
     filesystemService   = std::make_unique<FilesystemService>();
+    eventBus            = std::make_unique<EventBus>();
+    loopHooksService    = std::make_unique<LoopHooksService>();
 
     services.buzzer       = buzzerService.get();
     services.battery      = batteryService.get();
     services.storage      = storageService.get();
     services.random       = randomService.get();
     services.highResClock = highResClockService.get();
-    services.powerManager = powerService.get();
     services.filesystem   = filesystemService.get();
+    services.eventBus     = eventBus.get();
+    services.loopHooks    = loopHooksService.get();
+
+    Buttons::get().setEventBus(eventBus.get());
 }
 
 EspRuntime::~EspRuntime() = default;
@@ -160,7 +162,6 @@ void EspRuntime::initializeHardware() {
 
     ensureNvsInit();
 
-    PowerHelper::get();
     Shutdowner::get();
     Buttons::get();
 
@@ -170,7 +171,6 @@ void EspRuntime::initializeHardware() {
     }
 
     Shutdowner::get().install_isr();
-    PowerHelper::get().install_isr();
     Buttons::get().install_isr();
 
     I2cGlobal::get();
@@ -224,7 +224,7 @@ std::uint32_t EspClock::millis_impl() {
 void EspClock::sleep_ms_impl(std::uint32_t ms) {
     if (ms == 0)
         return;
-    PowerHelper::get().delay(static_cast<int>(ms), static_cast<int>(ms));
+    vTaskDelay(pdMS_TO_TICKS(ms));
 }
 
 } // namespace cardboy::backend::esp

Firmware/components/backend-esp/src/event_bus.cpp

@@ -0,0 +1,81 @@
+#include "cardboy/backend/esp/event_bus.hpp"
+
+#include "cardboy/sdk/event_bus.hpp"
+
+#include "freertos/portmacro.h"
+
+#include <algorithm>
+
+namespace cardboy::backend::esp {
+
+namespace {
+[[nodiscard]] TickType_t toTicks(std::uint32_t timeout_ms) {
+    if (timeout_ms == cardboy::sdk::IEventBus::kWaitForever)
+        return portMAX_DELAY;
+    return pdMS_TO_TICKS(timeout_ms);
+}
+} // namespace
+
+static void timerCallback(TimerHandle_t handle) {
+    auto* bus = static_cast<EventBus*>(pvTimerGetTimerID(handle));
+    if (bus)
+        bus->signal(cardboy::sdk::to_event_bits(cardboy::sdk::EventBusSignal::Timer));
+}
+
+EventBus::EventBus() :
+    group(xEventGroupCreate()), timer(xTimerCreate("EventBusTimer", pdMS_TO_TICKS(1), pdFALSE, this, timerCallback)) {}
+
+EventBus::~EventBus() {
+    if (timer)
+        xTimerDelete(timer, portMAX_DELAY);
+    if (group)
+        vEventGroupDelete(group);
+}
+
+void EventBus::signal(std::uint32_t bits) {
+    if (!group || bits == 0)
+        return;
+    xEventGroupSetBits(group, bits);
+}
+
+void EventBus::signalFromISR(std::uint32_t bits) {
+    if (!group || bits == 0)
+        return;
+    BaseType_t higherPriorityTaskWoken = pdFALSE;
+    xEventGroupSetBitsFromISR(group, bits, &higherPriorityTaskWoken);
+    if (higherPriorityTaskWoken == pdTRUE)
+        portYIELD_FROM_ISR(higherPriorityTaskWoken);
+}
+
+std::uint32_t EventBus::wait(std::uint32_t mask, std::uint32_t timeout_ms) {
+    if (!group || mask == 0)
+        return 0;
+    const EventBits_t bits = xEventGroupWaitBits(group, mask, pdTRUE, pdFALSE, toTicks(timeout_ms));
+    return static_cast<std::uint32_t>(bits & mask);
+}
+
+void EventBus::scheduleTimerSignal(std::uint32_t delay_ms) {
+    if (!timer)
+        return;
+    xTimerStop(timer, 0);
+
+    if (delay_ms == cardboy::sdk::IEventBus::kWaitForever)
+        return;
+
+    if (delay_ms == 0) {
+        signal(cardboy::sdk::to_event_bits(cardboy::sdk::EventBusSignal::Timer));
+        return;
+    }
+
+    const TickType_t ticks = std::max<TickType_t>(pdMS_TO_TICKS(delay_ms), 1);
+    if (xTimerChangePeriod(timer, ticks, 0) == pdPASS)
+        xTimerStart(timer, 0);
+}
+
+void EventBus::cancelTimerSignal() {
+    if (!timer)
+        return;
+    xTimerStop(timer, 0);
+}
+
+} // namespace cardboy::backend::esp

Firmware/components/backend-esp/src/power_helper.cpp

@@ -1,58 +0,0 @@
-//
-// Created by Stepan Usatiuk on 03.03.2025.
-//
-
-#include "cardboy/backend/esp/power_helper.hpp"
-
-#include "freertos/FreeRTOS.h"
-#include "freertos/task.h"
-
-PowerHelper& PowerHelper::get() {
-    static PowerHelper powerHelper;
-    return powerHelper;
-}
-bool PowerHelper::is_slow() const { return _slow; }
-void PowerHelper::set_slow(bool slow) {
-    _slow = slow;
-    if (_slow) {
-        xEventGroupClearBits(_event_group, 1);
-    } else {
-        xEventGroupSetBits(_event_group, 1);
-    }
-}
-
-BaseType_t PowerHelper::reset_slow_isr(BaseType_t* xHigherPriorityTaskWoken) {
-    _slow = false;
-    return xEventGroupSetBitsFromISR(_event_group, 1, xHigherPriorityTaskWoken);
-}
-
-static void wakeup(void* arg) {
-    BaseType_t xHigherPriorityTaskWoken, xResult;
-
-    xHigherPriorityTaskWoken = pdFALSE;
-    xResult                  = static_cast<PowerHelper*>(arg)->reset_slow_isr(&xHigherPriorityTaskWoken);
-    if (xResult != pdFAIL) {
-        portYIELD_FROM_ISR(xHigherPriorityTaskWoken);
-    };
-}
-
-PowerHelper::PowerHelper() : _event_group(xEventGroupCreate()) { set_slow(false); }
-
-void PowerHelper::delay(int slow_ms, int normal_ms) {
-    if (is_slow()) {
-        auto       cur_ticks      = xTaskGetTickCount();
-        TickType_t to_wait        = slow_ms / portTICK_PERIOD_MS;
-        TickType_t to_wait_normal = normal_ms / portTICK_PERIOD_MS;
-        auto       expected_ticks = cur_ticks + to_wait_normal;
-        xEventGroupWaitBits(_event_group, 1, pdFALSE, pdTRUE, to_wait);
-        auto realTicks = xTaskGetTickCount();
-        if (realTicks < expected_ticks) {
-            vTaskDelay(expected_ticks - realTicks);
-        }
-    } else {
-        vTaskDelay(normal_ms / portTICK_PERIOD_MS);
-    }
-}
-void PowerHelper::install_isr() {
-    // gpio_isr_handler_add(EXP_INT, wakeup, this);
-}

Firmware/sdk/apps/clock/src/clock_app.cpp

@@ -25,14 +25,14 @@ using Framebuffer = typename AppContext::Framebuffer;
 using Clock       = typename AppContext::Clock;
 
 struct TimeSnapshot {
-    bool     hasWallTime   = false;
-    int      hour24        = 0;
-    int      minute        = 0;
-    int      second        = 0;
-    int      year          = 0;
-    int      month         = 0;
-    int      day           = 0;
-    int      weekday       = 0;
+    bool          hasWallTime   = false;
+    int           hour24        = 0;
+    int           minute        = 0;
+    int           second        = 0;
+    int           year          = 0;
+    int           month         = 0;
+    int           day           = 0;
+    int           weekday       = 0;
     std::uint64_t uptimeSeconds = 0;
 };
 
@@ -42,8 +42,8 @@ public:
 
     void onStart() override {
         cancelRefreshTimer();
-        lastSnapshot = {};
-        dirty        = true;
+        lastSnapshot    = {};
+        dirty           = true;
         const auto snap = captureTime();
         renderIfNeeded(snap);
         lastSnapshot = snap;
@@ -69,8 +69,8 @@ private:
     Framebuffer& framebuffer;
     Clock&       clock;
 
-    bool            use24Hour    = true;
-    bool            dirty        = false;
+    bool                         use24Hour    = true;
+    bool                         dirty        = false;
     cardboy::sdk::AppTimerHandle refreshTimer = cardboy::sdk::kInvalidAppTimer;
 
     TimeSnapshot lastSnapshot{};
@@ -199,7 +199,7 @@ private:
         drawCenteredText(framebuffer, timeY + font16x8::kGlyphHeight * scaleLarge + 28, dateLine, scaleSmall, 1);
 
         if (!snap.hasWallTime) {
-            char              uptimeLine[32];
+            char                uptimeLine[32];
             const std::uint64_t days = snap.uptimeSeconds / 86400ULL;
             const std::uint64_t hrs  = (snap.uptimeSeconds / 3600ULL) % 24ULL;
             const std::uint64_t mins = (snap.uptimeSeconds / 60ULL) % 60ULL;
@@ -225,7 +225,7 @@ private:
 
 class ClockAppFactory final : public cardboy::sdk::IAppFactory {
 public:
-    const char*           name() const override { return kClockAppName; }
+    const char*                         name() const override { return kClockAppName; }
     std::unique_ptr<cardboy::sdk::IApp> create(cardboy::sdk::AppContext& context) override {
         return std::make_unique<ClockApp>(context);
     }

Firmware/sdk/apps/gameboy/CMakeLists.txt

@@ -1,10 +1,17 @@
 target_sources(cardboy_apps
         PRIVATE
         ${CMAKE_CURRENT_SOURCE_DIR}/src/gameboy_app.cpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/minigb_apu/minigb_apu.c
         ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/apps/peanut_gb.h
 )
 
 target_include_directories(cardboy_apps
         PUBLIC
         ${CMAKE_CURRENT_SOURCE_DIR}/include
+        ${CMAKE_CURRENT_SOURCE_DIR}
 )
+
+target_compile_definitions(cardboy_apps
+        PRIVATE
+        MINIGB_APU_AUDIO_FORMAT_S16SYS=1
+)

Firmware/sdk/apps/gameboy/minigb_apu/minigb_apu.c

@@ -0,0 +1,542 @@
+/**
+ * Game Boy APU emulator.
+ * Copyright (c) 2019 Mahyar Koshkouei <mk@deltabeard.com>
+ * Copyright (c) 2017 Alex Baines <alex@abaines.me.uk>
+ * minigb_apu is released under the terms of the MIT license.
+ *
+ * minigb_apu emulates the audio processing unit (APU) of the Game Boy. This
+ * project is based on MiniGBS by Alex Baines: https://github.com/baines/MiniGBS
+ */
+
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+
+#include "minigb_apu.h"
+
+#define DMG_CLOCK_FREQ_U	((unsigned)DMG_CLOCK_FREQ)
+#define AUDIO_NSAMPLES		(AUDIO_SAMPLES_TOTAL)
+
+#define MAX(a, b)		( a > b ? a : b )
+#define MIN(a, b)		( a <= b ? a : b )
+
+/* Factor in which values are multiplied to compensate for fixed-point
+ * arithmetic. Some hard-coded values in this project must be recreated. */
+#ifndef FREQ_INC_MULT
+# define FREQ_INC_MULT		105
+#endif
+/* Handles time keeping for sound generation.
+ * FREQ_INC_REF must be equal to, or larger than AUDIO_SAMPLE_RATE in order
+ * to avoid a division by zero error.
+ * Using a square of 2 simplifies calculations. */
+#define FREQ_INC_REF		(AUDIO_SAMPLE_RATE * FREQ_INC_MULT)
+
+#define MAX_CHAN_VOLUME		15
+
+static void set_note_freq(struct chan *c)
+{
+	/* Lowest expected value of freq is 64. */
+	uint32_t freq = (DMG_CLOCK_FREQ_U / 4) / (2048 - c->freq);
+	c->freq_inc = freq * (uint32_t)(FREQ_INC_REF / AUDIO_SAMPLE_RATE);
+}
+
+static void chan_enable(struct minigb_apu_ctx *ctx,
+		const uint_fast8_t i, const bool enable)
+{
+	uint8_t val;
+
+	ctx->chans[i].enabled = enable;
+	val = (ctx->audio_mem[0xFF26 - AUDIO_ADDR_COMPENSATION] & 0x80) |
+		(ctx->chans[3].enabled << 3) | (ctx->chans[2].enabled << 2) |
+		(ctx->chans[1].enabled << 1) | (ctx->chans[0].enabled << 0);
+
+	ctx->audio_mem[0xFF26 - AUDIO_ADDR_COMPENSATION] = val;
+}
+
+static void update_env(struct chan *c)
+{
+	c->env.counter += c->env.inc;
+
+	while (c->env.counter > FREQ_INC_REF) {
+		if (c->env.step) {
+			c->volume += c->env.up ? 1 : -1;
+			if (c->volume == 0 || c->volume == MAX_CHAN_VOLUME) {
+				c->env.inc = 0;
+			}
+			c->volume = MAX(0, MIN(MAX_CHAN_VOLUME, c->volume));
+		}
+		c->env.counter -= FREQ_INC_REF;
+	}
+}
+
+static void update_len(struct minigb_apu_ctx *ctx, struct chan *c)
+{
+	if (!c->len.enabled)
+		return;
+
+	c->len.counter += c->len.inc;
+	if (c->len.counter > FREQ_INC_REF) {
+		chan_enable(ctx, c - ctx->chans, 0);
+		c->len.counter = 0;
+	}
+}
+
+static bool update_freq(struct chan *c, uint32_t *pos)
+{
+	uint32_t inc = c->freq_inc - *pos;
+	c->freq_counter += inc;
+
+	if (c->freq_counter > FREQ_INC_REF) {
+		*pos		= c->freq_inc - (c->freq_counter - FREQ_INC_REF);
+		c->freq_counter = 0;
+		return true;
+	} else {
+		*pos = c->freq_inc;
+		return false;
+	}
+}
+
+static void update_sweep(struct chan *c)
+{
+	c->sweep.counter += c->sweep.inc;
+
+	while (c->sweep.counter > FREQ_INC_REF) {
+		if (c->sweep.shift) {
+			uint16_t inc = (c->sweep.freq >> c->sweep.shift);
+			if (c->sweep.down)
+				inc *= -1;
+
+			c->freq = c->sweep.freq + inc;
+			if (c->freq > 2047) {
+				c->enabled = 0;
+			} else {
+				set_note_freq(c);
+				c->sweep.freq = c->freq;
+			}
+		} else if (c->sweep.rate) {
+			c->enabled = 0;
+		}
+		c->sweep.counter -= FREQ_INC_REF;
+	}
+}
+
+static void update_square(struct minigb_apu_ctx *ctx, audio_sample_t *samples,
+		const bool ch2)
+{
+	struct chan *c = &ctx->chans[ch2];
+
+	if (!c->powered || !c->enabled)
+		return;
+
+	set_note_freq(c);
+
+	for (uint_fast16_t i = 0; i < AUDIO_NSAMPLES; i += 2) {
+		update_len(ctx, c);
+		if (!c->enabled)
+			return;
+
+		update_env(c);
+		if (!c->volume)
+			continue;
+
+		if (!ch2)
+			update_sweep(c);
+
+		uint32_t pos = 0;
+		uint32_t prev_pos = 0;
+		int32_t sample = 0;
+
+		while (update_freq(c, &pos)) {
+			c->square.duty_counter = (c->square.duty_counter + 1) & 7;
+			sample += ((pos - prev_pos) / c->freq_inc) * c->val;
+			c->val = (c->square.duty & (1 << c->square.duty_counter)) ?
+				VOL_INIT_MAX / MAX_CHAN_VOLUME :
+				VOL_INIT_MIN / MAX_CHAN_VOLUME;
+			prev_pos = pos;
+		}
+
+		sample += c->val;
+		sample *= c->volume;
+		sample /= 4;
+
+		samples[i + 0] += sample * c->on_left * ctx->vol_l;
+		samples[i + 1] += sample * c->on_right * ctx->vol_r;
+	}
+}
+
+static uint8_t wave_sample(struct minigb_apu_ctx *ctx,
+		const unsigned int pos, const unsigned int volume)
+{
+	uint8_t sample;
+
+	sample =  ctx->audio_mem[(0xFF30 + pos / 2) - AUDIO_ADDR_COMPENSATION];
+	if (pos & 1) {
+		sample &= 0xF;
+	} else {
+		sample >>= 4;
+	}
+	return volume ? (sample >> (volume - 1)) : 0;
+}
+
+static void update_wave(struct minigb_apu_ctx *ctx, audio_sample_t *samples)
+{
+	struct chan *c = &ctx->chans[2];
+
+	if (!c->powered || !c->enabled || !c->volume)
+		return;
+
+	set_note_freq(c);
+	c->freq_inc *= 2;
+
+	for (uint_fast16_t i = 0; i < AUDIO_NSAMPLES; i += 2) {
+		update_len(ctx, c);
+		if (!c->enabled)
+			return;
+
+		uint32_t pos = 0;
+		uint32_t prev_pos = 0;
+		audio_sample_t sample = 0;
+
+		c->wave.sample = wave_sample(ctx, c->val, c->volume);
+
+		while (update_freq(c, &pos)) {
+			c->val = (c->val + 1) & 31;
+			sample += ((pos - prev_pos) / c->freq_inc) *
+				((audio_sample_t)c->wave.sample - 8) *
+					(AUDIO_SAMPLE_MAX/64);
+			c->wave.sample = wave_sample(ctx, c->val, c->volume);
+			prev_pos  = pos;
+		}
+
+		sample += ((audio_sample_t)c->wave.sample - 8) *
+				(audio_sample_t)(AUDIO_SAMPLE_MAX/64);
+		{
+			/* First element is unused. */
+			audio_sample_t div[] = { AUDIO_SAMPLE_MAX, 1, 2, 4 };
+			sample = sample / (div[c->volume]);
+		}
+
+		sample /= 4;
+		samples[i + 0] += sample * c->on_left * ctx->vol_l;
+		samples[i + 1] += sample * c->on_right * ctx->vol_r;
+	}
+}
+
+static void update_noise(struct minigb_apu_ctx *ctx, audio_sample_t *samples)
+{
+	struct chan *c = &ctx->chans[3];
+
+	if (c->freq >= 14)
+		c->enabled = 0;
+
+	if (!c->powered || !c->enabled)
+		return;
+
+	{
+		const uint32_t lfsr_div_lut[] = {
+			8, 16, 32, 48, 64, 80, 96, 112
+		};
+		uint32_t freq;
+
+		freq = DMG_CLOCK_FREQ_U / (lfsr_div_lut[c->noise.lfsr_div] << c->freq);
+		c->freq_inc = freq * (uint32_t)(FREQ_INC_REF / AUDIO_SAMPLE_RATE);
+	}
+
+	for (uint_fast16_t i = 0; i < AUDIO_NSAMPLES; i += 2) {
+		update_len(ctx, c);
+		if (!c->enabled)
+			return;
+
+		update_env(c);
+		if (!c->volume)
+			continue;
+
+		uint32_t pos      = 0;
+		uint32_t prev_pos = 0;
+		int32_t sample    = 0;
+
+		while (update_freq(c, &pos)) {
+			c->noise.lfsr_reg = (c->noise.lfsr_reg << 1) |
+				(c->val >= VOL_INIT_MAX/MAX_CHAN_VOLUME);
+
+			if (c->noise.lfsr_wide) {
+				c->val = !(((c->noise.lfsr_reg >> 14) & 1) ^
+						((c->noise.lfsr_reg >> 13) & 1)) ?
+					VOL_INIT_MAX / MAX_CHAN_VOLUME :
+					VOL_INIT_MIN / MAX_CHAN_VOLUME;
+			} else {
+				c->val = !(((c->noise.lfsr_reg >> 6) & 1) ^
+						((c->noise.lfsr_reg >> 5) & 1)) ?
+					VOL_INIT_MAX / MAX_CHAN_VOLUME :
+					VOL_INIT_MIN / MAX_CHAN_VOLUME;
+			}
+
+			sample += ((pos - prev_pos) / c->freq_inc) * c->val;
+			prev_pos = pos;
+		}
+
+		sample += c->val;
+		sample *= c->volume;
+		sample /= 4;
+
+		samples[i + 0] += sample * c->on_left * ctx->vol_l;
+		samples[i + 1] += sample * c->on_right * ctx->vol_r;
+	}
+}
+
+/**
+ * SDL2 style audio callback function.
+ */
+void minigb_apu_audio_callback(struct minigb_apu_ctx *ctx,
+		audio_sample_t *stream)
+{
+	memset(stream, 0, AUDIO_SAMPLES_TOTAL * sizeof(audio_sample_t));
+	update_square(ctx, stream, 0);
+	update_square(ctx, stream, 1);
+	update_wave(ctx, stream);
+	update_noise(ctx, stream);
+}
+
+static void chan_trigger(struct minigb_apu_ctx *ctx, uint_fast8_t i)
+{
+	struct chan *c = &ctx->chans[i];
+
+	chan_enable(ctx, i, 1);
+	c->volume = c->volume_init;
+
+	// volume envelope
+	{
+		/* LUT created in Julia with:
+		 * `(FREQ_INC_MULT * 64)./vcat(8, 1:7)`
+		 * Must be recreated when FREQ_INC_MULT modified.
+		 */
+		const uint32_t inc_lut[8] = {
+#if FREQ_INC_MULT == 16
+			128, 1024, 512, 341,
+			256,  205, 171, 146
+#elif FREQ_INC_MULT == 64
+            512,  4096, 2048, 1365,
+            1024,  819,  683,  585
+#elif FREQ_INC_MULT == 105
+            /* Multiples of 105 provide integer values. */
+            840,  6720, 3360, 2240,
+            1680, 1344, 1120,  960
+#else
+#error "LUT not calculated for this value of FREQ_INC_MULT"
+#endif
+		};
+		uint8_t val;
+
+		val = ctx->audio_mem[(0xFF12 + (i * 5)) - AUDIO_ADDR_COMPENSATION];
+
+		c->env.step = val & 0x7;
+		c->env.up   = val & 0x8;
+		c->env.inc  = inc_lut[c->env.step];
+		c->env.counter = 0;
+	}
+
+	// freq sweep
+	if (i == 0) {
+		uint8_t val = ctx->audio_mem[0xFF10 - AUDIO_ADDR_COMPENSATION];
+
+		c->sweep.freq  = c->freq;
+		c->sweep.rate  = (val >> 4) & 0x07;
+		c->sweep.down  = (val & 0x08);
+		c->sweep.shift = (val & 0x07);
+		c->sweep.inc   = c->sweep.rate ?
+			((128u * FREQ_INC_REF) / (c->sweep.rate * AUDIO_SAMPLE_RATE)) : 0;
+		c->sweep.counter = FREQ_INC_REF;
+	}
+
+	int len_max = 64;
+
+	if (i == 2) { // wave
+		len_max = 256;
+		c->val = 0;
+	} else if (i == 3) { // noise
+		c->noise.lfsr_reg = 0xFFFF;
+		c->val = VOL_INIT_MIN / MAX_CHAN_VOLUME;
+	}
+
+	c->len.inc = (256u * FREQ_INC_REF) / (AUDIO_SAMPLE_RATE * (len_max - c->len.load));
+	c->len.counter = 0;
+}
+
+/**
+ * Read audio register.
+ * \param addr	Address of audio register. Must be 0xFF10 <= addr <= 0xFF3F.
+ *				This is not checked in this function.
+ * \return	Byte at address.
+ */
+uint8_t minigb_apu_audio_read(struct minigb_apu_ctx *ctx, const uint16_t addr)
+{
+	static const uint8_t ortab[] = {
+		0x80, 0x3f, 0x00, 0xff, 0xbf,
+		0xff, 0x3f, 0x00, 0xff, 0xbf,
+		0x7f, 0xff, 0x9f, 0xff, 0xbf,
+		0xff, 0xff, 0x00, 0x00, 0xbf,
+		0x00, 0x00, 0x70,
+		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00
+	};
+
+	return ctx->audio_mem[addr - AUDIO_ADDR_COMPENSATION] |
+		ortab[addr - AUDIO_ADDR_COMPENSATION];
+}
+
+/**
+ * Write audio register.
+ * \param addr	Address of audio register. Must be 0xFF10 <= addr <= 0xFF3F.
+ *				This is not checked in this function.
+ * \param val	Byte to write at address.
+ */
+void minigb_apu_audio_write(struct minigb_apu_ctx *ctx,
+		const uint16_t addr, const uint8_t val)
+{
+	/* Find sound channel corresponding to register address. */
+	uint_fast8_t i;
+
+	if(addr == 0xFF26)
+	{
+		ctx->audio_mem[addr - AUDIO_ADDR_COMPENSATION] = val & 0x80;
+		/* On APU power off, clear all registers apart from wave
+		 * RAM. */
+		if((val & 0x80) == 0)
+		{
+			memset(ctx->audio_mem,
+					0x00, 0xFF26 - AUDIO_ADDR_COMPENSATION);
+			ctx->chans[0].enabled = false;
+			ctx->chans[1].enabled = false;
+			ctx->chans[2].enabled = false;
+			ctx->chans[3].enabled = false;
+		}
+
+		return;
+	}
+
+	/* Ignore register writes if APU powered off. */
+	if(ctx->audio_mem[0xFF26 - AUDIO_ADDR_COMPENSATION] == 0x00)
+		return;
+
+	ctx->audio_mem[addr - AUDIO_ADDR_COMPENSATION] = val;
+	i = (addr - AUDIO_ADDR_COMPENSATION) / 5;
+
+	switch (addr) {
+	case 0xFF12:
+	case 0xFF17:
+	case 0xFF21: {
+		ctx->chans[i].volume_init = val >> 4;
+		ctx->chans[i].powered     = (val >> 3) != 0;
+
+		// "zombie mode" stuff, needed for Prehistorik Man and probably
+		// others
+		if (ctx->chans[i].powered && ctx->chans[i].enabled) {
+			if ((ctx->chans[i].env.step == 0 && ctx->chans[i].env.inc != 0)) {
+				if (val & 0x08) {
+					ctx->chans[i].volume++;
+				} else {
+					ctx->chans[i].volume += 2;
+				}
+			} else {
+				ctx->chans[i].volume = 16 - ctx->chans[i].volume;
+			}
+
+			ctx->chans[i].volume &= 0x0F;
+			ctx->chans[i].env.step = val & 0x07;
+		}
+	} break;
+
+	case 0xFF1C:
+		ctx->chans[i].volume = ctx->chans[i].volume_init = (val >> 5) & 0x03;
+		break;
+
+	case 0xFF11:
+	case 0xFF16:
+	case 0xFF20: {
+		const uint8_t duty_lookup[] = { 0x10, 0x30, 0x3C, 0xCF };
+		ctx->chans[i].len.load = val & 0x3f;
+		ctx->chans[i].square.duty = duty_lookup[val >> 6];
+		break;
+	}
+
+	case 0xFF1B:
+		ctx->chans[i].len.load = val;
+		break;
+
+	case 0xFF13:
+	case 0xFF18:
+	case 0xFF1D:
+		ctx->chans[i].freq &= 0xFF00;
+		ctx->chans[i].freq |= val;
+		break;
+
+	case 0xFF1A:
+		ctx->chans[i].powered = (val & 0x80) != 0;
+		chan_enable(ctx, i, val & 0x80);
+		break;
+
+	case 0xFF14:
+	case 0xFF19:
+	case 0xFF1E:
+		ctx->chans[i].freq &= 0x00FF;
+		ctx->chans[i].freq |= ((val & 0x07) << 8);
+		/* Intentional fall-through. */
+	case 0xFF23:
+		ctx->chans[i].len.enabled = val & 0x40;
+		if (val & 0x80)
+			chan_trigger(ctx, i);
+
+		break;
+
+	case 0xFF22:
+		ctx->chans[3].freq = val >> 4;
+		ctx->chans[3].noise.lfsr_wide = !(val & 0x08);
+		ctx->chans[3].noise.lfsr_div = val & 0x07;
+		break;
+
+	case 0xFF24:
+	{
+		ctx->vol_l = ((val >> 4) & 0x07);
+		ctx->vol_r = (val & 0x07);
+		break;
+	}
+
+	case 0xFF25:
+		for (uint_fast8_t j = 0; j < 4; j++) {
+			ctx->chans[j].on_left  = (val >> (4 + j)) & 1;
+			ctx->chans[j].on_right = (val >> j) & 1;
+		}
+		break;
+	}
+}
+
+void minigb_apu_audio_init(struct minigb_apu_ctx *ctx)
+{
+	/* Initialise channels and samples. */
+	memset(ctx->chans, 0, sizeof(ctx->chans));
+	ctx->chans[0].val = ctx->chans[1].val = -1;
+
+	/* Initialise IO registers. */
+	{
+		const uint8_t regs_init[] = { 0x80, 0xBF, 0xF3, 0xFF, 0x3F,
+					      0xFF, 0x3F, 0x00, 0xFF, 0x3F,
+					      0x7F, 0xFF, 0x9F, 0xFF, 0x3F,
+					      0xFF, 0xFF, 0x00, 0x00, 0x3F,
+					      0x77, 0xF3, 0xF1 };
+
+		for(uint_fast8_t i = 0; i < sizeof(regs_init); ++i)
+			minigb_apu_audio_write(ctx, 0xFF10 + i, regs_init[i]);
+	}
+
+	/* Initialise Wave Pattern RAM. */
+	{
+		const uint8_t wave_init[] = { 0xac, 0xdd, 0xda, 0x48,
+					      0x36, 0x02, 0xcf, 0x16,
+					      0x2c, 0x04, 0xe5, 0x2c,
+					      0xac, 0xdd, 0xda, 0x48 };
+
+		for(uint_fast8_t i = 0; i < sizeof(wave_init); ++i)
+			minigb_apu_audio_write(ctx, 0xFF30 + i, wave_init[i]);
+	}
+}

Firmware/sdk/apps/gameboy/minigb_apu/minigb_apu.h

@@ -0,0 +1,149 @@
+/**
+ * minigb_apu is released under the terms listed within the LICENSE file.
+ *
+ * minigb_apu emulates the audio processing unit (APU) of the Game Boy. This
+ * project is based on MiniGBS by Alex Baines: https://github.com/baines/MiniGBS
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#ifndef AUDIO_SAMPLE_RATE
+# define AUDIO_SAMPLE_RATE	20000
+#endif
+
+/* The audio output format is in platform native endian. */
+#if defined(MINIGB_APU_AUDIO_FORMAT_S16SYS)
+typedef int16_t audio_sample_t;
+# define AUDIO_SAMPLE_MAX INT16_MAX
+# define AUDIO_SAMPLE_MIN INT16_MIN
+# define VOL_INIT_MAX (AUDIO_SAMPLE_MAX/8)
+# define VOL_INIT_MIN (AUDIO_SAMPLE_MIN/8)
+#elif defined(MINIGB_APU_AUDIO_FORMAT_S32SYS)
+typedef int32_t audio_sample_t;
+# define AUDIO_SAMPLE_MAX INT32_MAX
+# define AUDIO_SAMPLE_MIN INT32_MIN
+# define VOL_INIT_MAX (INT32_MAX/8)
+# define VOL_INIT_MIN (INT32_MIN/8)
+#else
+#error MiniGB APU: Invalid or unsupported audio format selected
+#endif
+
+#define DMG_CLOCK_FREQ		4194304.0
+#define SCREEN_REFRESH_CYCLES	70224.0
+#define VERTICAL_SYNC		(DMG_CLOCK_FREQ/SCREEN_REFRESH_CYCLES)
+
+/* Number of audio samples in each channel. */
+#define AUDIO_SAMPLES		((unsigned)(AUDIO_SAMPLE_RATE / VERTICAL_SYNC))
+/* Number of audio channels. The audio output is in interleaved stereo format.*/
+#define AUDIO_CHANNELS		2
+/* Number of audio samples output in each audio_callback call. */
+#define AUDIO_SAMPLES_TOTAL	(AUDIO_SAMPLES * 2)
+
+#define AUDIO_MEM_SIZE		(0xFF3F - 0xFF10 + 1)
+#define AUDIO_ADDR_COMPENSATION	0xFF10
+
+struct chan_len_ctr {
+	uint8_t load;
+	uint8_t enabled;
+	uint32_t counter;
+	uint32_t inc;
+};
+
+struct chan_vol_env {
+	uint8_t step;
+	uint8_t up;
+	uint32_t counter;
+	uint32_t inc;
+};
+
+struct chan_freq_sweep {
+	uint8_t rate;
+	uint8_t shift;
+	uint8_t down;
+	uint16_t freq;
+	uint32_t counter;
+	uint32_t inc;
+};
+
+struct chan {
+	uint8_t enabled;
+	uint8_t powered;
+	uint8_t on_left;
+	uint8_t on_right;
+
+	uint8_t volume;
+	uint8_t volume_init;
+
+	uint16_t freq;
+	uint32_t freq_counter;
+	uint32_t freq_inc;
+
+	int32_t val;
+
+	struct chan_len_ctr    len;
+	struct chan_vol_env    env;
+	struct chan_freq_sweep sweep;
+
+	union {
+		struct {
+			uint8_t duty;
+			uint8_t duty_counter;
+		} square;
+		struct {
+			uint16_t lfsr_reg;
+			uint8_t  lfsr_wide;
+			uint8_t  lfsr_div;
+		} noise;
+		struct {
+			uint8_t sample;
+		} wave;
+	};
+};
+
+struct minigb_apu_ctx {
+	struct chan chans[4];
+	int32_t vol_l, vol_r;
+
+	/**
+	 * Memory holding audio registers between 0xFF10 and 0xFF3F inclusive.
+	 */
+	uint8_t audio_mem[AUDIO_MEM_SIZE];
+};
+
+/**
+ * Fill allocated buffer "stream" with AUDIO_SAMPLES_TOTAL number of 16-bit
+ * signed samples (native endian order) in stereo interleaved format.
+ * Each call corresponds to the time taken for each VSYNC in the Game Boy.
+ *
+ * \param ctx Library context. Must be initialised with audio_init().
+ * \param stream Allocated pointer to store audio samples. Must be at least
+ *		AUDIO_SAMPLES_TOTAL in size.
+ */
+void minigb_apu_audio_callback(struct minigb_apu_ctx *ctx,
+		audio_sample_t *stream);
+
+/**
+ * Read audio register at given address "addr".
+ * \param ctx Library context. Must be initialised with audio_init().
+ * \param addr Address of registers to read. Must be within 0xFF10 and 0xFF3F,
+ *	inclusive.
+ */
+uint8_t minigb_apu_audio_read(struct minigb_apu_ctx *ctx, const uint16_t addr);
+
+/**
+ * Write "val" to audio register at given address "addr".
+ * \param ctx Library context. Must be initialised with audio_init().
+ * \param addr Address of registers to read. Must be within 0xFF10 and 0xFF3F,
+ *	inclusive.
+ * \param val Value to write to address.
+ */
+void minigb_apu_audio_write(struct minigb_apu_ctx *ctx,
+		const uint16_t addr, const uint8_t val);
+
+/**
+ * Initialise audio driver.
+ * \param ctx Library context.
+ */
+void minigb_apu_audio_init(struct minigb_apu_ctx *ctx);

Firmware/sdk/apps/gameboy/src/gameboy_app.cpp

@@ -1,6 +1,33 @@
 #include "cardboy/apps/gameboy_app.hpp"
+
+uint8_t audio_read(uint16_t addr);
+void    audio_write(uint16_t addr, uint8_t value);
+
+namespace {
+using AudioReadThunk  = uint8_t (*)(void*, uint16_t);
+using AudioWriteThunk = void (*)(void*, uint16_t, uint8_t);
+
+void*           gAudioCtx        = nullptr;
+AudioReadThunk  gAudioReadThunk  = nullptr;
+AudioWriteThunk gAudioWriteThunk = nullptr;
+} // namespace
+
+uint8_t audio_read(uint16_t addr) {
+    if (gAudioReadThunk && gAudioCtx)
+        return gAudioReadThunk(gAudioCtx, addr);
+    return 0xFF;
+}
+
+void audio_write(uint16_t addr, uint8_t value) {
+    if (gAudioWriteThunk && gAudioCtx)
+        gAudioWriteThunk(gAudioCtx, addr, value);
+}
+
+#define ENABLE_SOUND 1
 #include "cardboy/apps/peanut_gb.h"
 
+#include "cardboy/apps/menu_app.hpp"
+
 #include "cardboy/gfx/font16x8.hpp"
 #include "cardboy/sdk/app_framework.hpp"
 #include "cardboy/sdk/app_system.hpp"
@@ -12,17 +39,84 @@
 
 #include <algorithm>
 #include <array>
+#include <atomic>
 #include <cctype>
 #include <cerrno>
 #include <chrono>
+#include <cmath>
 #include <cstdint>
 #include <cstdio>
 #include <cstring>
 #include <dirent.h>
+#include <mutex>
 #include <string>
 #include <string_view>
 #include <sys/stat.h>
 #include <vector>
+#include "esp_pm.h"
+
+#include "driver/gpio.h"
+#include "driver/gptimer.h"
+#include "hal/sdm_types.h"
+#include "esp_attr.h"
+#include "esp_err.h"
+#include "esp_heap_caps.h"
+#include "esp_log.h"
+#include "esp_check.h"
+#include "esp_pm.h"
+#include "esp_clk_tree.h"
+#include "driver/gpio.h"
+#include "driver/sdm.h"
+#include "hal/gpio_hal.h"
+#include "hal/sdm_hal.h"
+#include "hal/sdm_ll.h"
+#include "hal/hal_utils.h"
+#include "soc/sdm_periph.h"
+
+
+struct sdm_group_t {
+    int group_id;               // Group ID, index from 0
+    portMUX_TYPE spinlock;      // to protect per-group register level concurrent access
+    sdm_hal_context_t hal; // hal context
+    sdm_channel_t *channels[SOC_SDM_CHANNELS_PER_GROUP]; // array of sdm channels
+    sdm_clock_source_t clk_src; // Clock source
+};
+struct sdm_platform_t {
+    _lock_t mutex;                                 // platform level mutex lock
+    sdm_group_t *groups[SOC_SDM_GROUPS]; // sdm group pool
+    int group_ref_counts[SOC_SDM_GROUPS];     // reference count used to protect group install/uninstall
+};
+
+typedef enum {
+    SDM_FSM_INIT,
+    SDM_FSM_ENABLE,
+} sdm_fsm_t;
+#define SDM_PM_LOCK_NAME_LEN_MAX 16
+
+struct sdm_channel_t {
+    sdm_group_t *group;         // which group the sdm channel belongs to
+    uint32_t chan_id;                // allocated channel numerical ID
+    int gpio_num;                    // GPIO number
+    uint32_t sample_rate_hz;         // Sample rate, in Hz
+    portMUX_TYPE spinlock;           // to protect per-channels resources concurrently accessed by task and ISR handler
+    esp_pm_lock_handle_t pm_lock;    // PM lock, for glitch filter, as that module can only be functional under APB
+    sdm_fsm_t fsm;              // FSM state
+#if CONFIG_PM_ENABLE
+    char pm_lock_name[SDM_PM_LOCK_NAME_LEN_MAX]; // pm lock name
+#endif
+};
+
+
+#include "hal/sdm_hal.h"
+#include "hal/sdm_ll.h"
+#include "driver/sdm.h"
+#include "esp_err.h"
+#include "esp_log.h"
+#include "esp_random.h"
+
+extern "C" {
+#include "minigb_apu/minigb_apu.h"
+}
 
 #define GAMEBOY_PERF_METRICS 0
 
@@ -38,6 +132,12 @@
 
 static constexpr uint8_t kPattern2x2[4] = {0, 2, 3, 1}; // [ (y&1)<<1 | (x&1) ]
 
+static constexpr bool       kEnableGbPwmPrototype  = true;
+static constexpr gpio_num_t kGbPwmPrototypePin     = GPIO_NUM_25;
+static constexpr uint32_t   kGbPwmSampleRateHz     = AUDIO_SAMPLE_RATE;
+static constexpr uint32_t   kGbPwmCarrierHz        = 8000000;
+static constexpr int        kGbSdmHardwareChannels = 4; // ESP32-H2 SDM offers up to four channels per TRM Section 4.4
+
 // exact predicate per your shouldPixelBeOn
 static constexpr uint8_t on_bit(uint8_t v, uint8_t threshold) {
     if (v >= 3)
@@ -106,6 +206,22 @@ namespace {
 constexpr int kMenuStartY  = 48;
 constexpr int kMenuSpacing = font16x8::kGlyphHeight + 6;
 
+// Compile-time toggles for APU channel mix
+#ifndef GB_BUZZER_ENABLE_CH1
+#define GB_BUZZER_ENABLE_CH1 1
+#endif
+#ifndef GB_BUZZER_ENABLE_CH2
+#define GB_BUZZER_ENABLE_CH2 1
+#endif
+#ifndef GB_BUZZER_ENABLE_CH3
+#define GB_BUZZER_ENABLE_CH3 1
+#endif
+#ifndef GB_BUZZER_ENABLE_CH4
+#define GB_BUZZER_ENABLE_CH4 1
+#endif
+
+class GameboyApp;
+
 
 using cardboy::sdk::AppContext;
 using cardboy::sdk::AppEvent;
@@ -174,10 +290,15 @@ public:
         context(ctx), framebuffer(ctx.framebuffer), filesystem(ctx.filesystem()), highResClock(ctx.highResClock()) {}
 
     void onStart() override {
+        ::gAudioCtx        = this;
+        ::gAudioReadThunk  = &GameboyApp::audioReadThunk;
+        ::gAudioWriteThunk = &GameboyApp::audioWriteThunk;
+        apu.attach(this);
+        apu.reset();
         cancelTick();
         frameDelayCarryUs = 0;
         GB_PERF_ONLY(perf.resetAll();)
-        prevInput = {};
+        prevInput = context.input.readState();
         statusMessage.clear();
         resetFpsStats();
         scaleMode = ScaleMode::FullHeightWide;
@@ -193,6 +314,13 @@ public:
         frameDelayCarryUs = 0;
         GB_PERF_ONLY(perf.maybePrintAggregate(true);)
         unloadRom();
+        apu.reset();
+        apu.attach(nullptr);
+        if (::gAudioCtx == this) {
+            ::gAudioCtx        = nullptr;
+            ::gAudioReadThunk  = nullptr;
+            ::gAudioWriteThunk = nullptr;
+        }
     }
 
     void handleEvent(const AppEvent& event) override {
@@ -250,6 +378,8 @@ public:
                 gb_run_frame(&gb);
                 GB_PERF_ONLY(perf.runUs = nowMicros() - runStartUs;)
 
+                apu.generateFrameAudio();
+
                 GB_PERF_ONLY(const uint64_t renderStartUs = nowMicros();)
                 renderGameFrame();
                 GB_PERF_ONLY(perf.renderUs = nowMicros() - renderStartUs;)
@@ -266,7 +396,224 @@ public:
         GB_PERF_ONLY(perf.maybePrintAggregate();)
     }
 
+    [[nodiscard]] uint8_t audioReadRegister(uint16_t addr) const { return apu.read(addr); }
+    void                  audioWriteRegister(uint16_t addr, uint8_t value) { apu.write(addr, value); }
+
 private:
+    class SimpleApu {
+    public:
+        SimpleApu() {}
+
+        void attach(GameboyApp* ownerInstance) { owner = ownerInstance; }
+
+        void reset() {
+            stopAudio();
+            minigb_apu_audio_init(&ctx);
+            frameCursor = kFramesPerBuffer;
+            lastDensity = 0;
+        }
+
+        [[nodiscard]] uint8_t read(uint16_t addr) const {
+            return minigb_apu_audio_read(const_cast<minigb_apu_ctx*>(&ctx), addr);
+        }
+
+        void write(uint16_t addr, uint8_t value) { minigb_apu_audio_write(&ctx, addr, value); }
+
+        void generateFrameAudio() {
+            if (!kEnableGbPwmPrototype)
+                return;
+            minigb_apu_audio_callback(&ctx, playbackBuf.data());
+            // pendingReady = true;
+        }
+
+        void startAudio() {
+            if (!kEnableGbPwmPrototype)
+                return;
+            if (audioRunning)
+                return;
+            stopAudio();
+            {
+                // std::lock_guard<std::mutex> lock(bufferMutex);
+                pendingReady = false;
+                frameCursor  = kFramesPerBuffer;
+            }
+            generateFrameAudio();
+            frameCursor = 0;
+
+            sdm_config_t config{};
+            config.gpio_num       = static_cast<int>(kGbPwmPrototypePin);
+            config.clk_src        = SDM_CLK_SRC_DEFAULT;
+            config.sample_rate_hz = kGbPwmCarrierHz;
+
+            esp_err_t err = sdm_new_channel(&config, &sdmChannel);
+            if (err != ESP_OK) {
+                ESP_LOGE(kAudioLogTag, "sdm_new_channel failed (%s)", esp_err_to_name(err));
+                sdmChannel = nullptr;
+                return;
+            }
+            err = sdm_channel_enable(sdmChannel);
+            if (err != ESP_OK) {
+                ESP_LOGE(kAudioLogTag, "sdm_channel_enable failed (%s)", esp_err_to_name(err));
+                sdm_del_channel(sdmChannel);
+                sdmChannel = nullptr;
+                return;
+            }
+
+            auto cleanupTimer = [&]() {
+                if (!audioTimer)
+                    return;
+                gptimer_stop(audioTimer);
+                gptimer_disable(audioTimer);
+                gptimer_del_timer(audioTimer);
+                audioTimer = nullptr;
+            };
+
+            gptimer_config_t timerConfig{};
+            timerConfig.clk_src       = GPTIMER_CLK_SRC_DEFAULT;
+            timerConfig.direction     = GPTIMER_COUNT_UP;
+            timerConfig.resolution_hz = kTimerResolutionHz;
+
+            err = gptimer_new_timer(&timerConfig, &audioTimer);
+            if (err != ESP_OK) {
+                ESP_LOGE(kAudioLogTag, "gptimer_new_timer failed (%s)", esp_err_to_name(err));
+                sdm_channel_disable(sdmChannel);
+                sdm_del_channel(sdmChannel);
+                sdmChannel = nullptr;
+                return;
+            }
+
+            gptimer_event_callbacks_t callbacks{};
+            callbacks.on_alarm = &SimpleApu::audioTimerThunk;
+            err                = gptimer_register_event_callbacks(audioTimer, &callbacks, this);
+            if (err != ESP_OK) {
+                ESP_LOGE(kAudioLogTag, "gptimer_register_event_callbacks failed (%s)", esp_err_to_name(err));
+                cleanupTimer();
+                sdm_channel_disable(sdmChannel);
+                sdm_del_channel(sdmChannel);
+                sdmChannel = nullptr;
+                return;
+            }
+
+            const uint32_t ticksPerSample = std::max<uint32_t>(1, timerConfig.resolution_hz / kGbPwmSampleRateHz);
+
+            gptimer_alarm_config_t alarmConfig{};
+            alarmConfig.reload_count               = 0;
+            alarmConfig.alarm_count                = ticksPerSample;
+            alarmConfig.flags.auto_reload_on_alarm = true;
+
+            err = gptimer_set_alarm_action(audioTimer, &alarmConfig);
+            if (err != ESP_OK) {
+                ESP_LOGE(kAudioLogTag, "gptimer_set_alarm_action failed (%s)", esp_err_to_name(err));
+                cleanupTimer();
+                sdm_channel_disable(sdmChannel);
+                sdm_del_channel(sdmChannel);
+                sdmChannel = nullptr;
+                return;
+            }
+
+            err = gptimer_enable(audioTimer);
+            if (err != ESP_OK) {
+                ESP_LOGE(kAudioLogTag, "gptimer_enable failed (%s)", esp_err_to_name(err));
+                cleanupTimer();
+                sdm_channel_disable(sdmChannel);
+                sdm_del_channel(sdmChannel);
+                sdmChannel = nullptr;
+                return;
+            }
+
+            err = gptimer_start(audioTimer);
+            if (err != ESP_OK) {
+                ESP_LOGE(kAudioLogTag, "gptimer_start failed (%s)", esp_err_to_name(err));
+                cleanupTimer();
+                sdm_channel_disable(sdmChannel);
+                sdm_del_channel(sdmChannel);
+                sdmChannel = nullptr;
+                return;
+            }
+
+            audioRunning = true;
+            lastDensity  = 0;
+            sdm_channel_set_pulse_density(sdmChannel, 0);
+            ESP_LOGI(kAudioLogTag, "sigma-delta audio active on GPIO%d (%u Hz sample, %u Hz carrier)",
+                     static_cast<int>(kGbPwmPrototypePin), kGbPwmSampleRateHz, kGbPwmCarrierHz);
+        }
+
+        void stopAudio() {
+            if (audioTimer) {
+                gptimer_stop(audioTimer);
+                gptimer_disable(audioTimer);
+                gptimer_del_timer(audioTimer);
+                audioTimer = nullptr;
+            }
+            if (sdmChannel) {
+                sdm_channel_set_pulse_density(sdmChannel, 0);
+                sdm_channel_disable(sdmChannel);
+                sdm_del_channel(sdmChannel);
+                sdmChannel = nullptr;
+            }
+            audioRunning = false;
+            frameCursor  = kFramesPerBuffer;
+            lastDensity  = 0;
+        }
+
+        bool computeEffectiveTone(uint32_t& outFreqHz, uint8_t& outLoudness) const {
+            (void) outFreqHz;
+            (void) outLoudness;
+            return false;
+        }
+
+    private:
+        static constexpr const char* kAudioLogTag       = "gb_sdm";
+        static constexpr uint16_t    kBaseAddr          = 0xFF10;
+        static constexpr uint16_t    kEndAddr           = 0xFF3F;
+        static constexpr std::size_t kFramesPerBuffer   = AUDIO_SAMPLES;
+        static constexpr std::size_t kSamplesPerBuffer  = AUDIO_SAMPLES_TOTAL;
+        static constexpr uint32_t    kTimerResolutionHz = 1'000'000;
+
+        static constexpr bool inRange(uint16_t addr) { return addr >= kBaseAddr && addr <= kEndAddr; }
+
+        static IRAM_ATTR bool audioTimerThunk(gptimer_handle_t, const gptimer_alarm_event_data_t*, void* userData) {
+            auto* self = static_cast<SimpleApu*>(userData);
+            if (self)
+                self->handleAudioTick();
+            return true;
+        }
+
+        IRAM_ATTR void handleAudioTick() {
+            if (!audioRunning || !sdmChannel)
+                return;
+
+            if (frameCursor >= kFramesPerBuffer) {
+                frameCursor = 0;
+            }
+
+            const std::size_t offset = frameCursor * 2;
+            ++frameCursor;
+
+            const audio_sample_t sample   = playbackBuf[offset];
+
+            int32_t density = sample >> 7;
+            if (density > 127)
+                density = 127;
+            else if (density < -128)
+                density = -128;
+            sdm_group_t *group = sdmChannel->group;
+            int chan_id = sdmChannel->chan_id;
+
+            sdm_ll_set_pulse_density(group->hal.dev, chan_id, density);
+        }
+
+        GameboyApp*                                   owner = nullptr;
+        minigb_apu_ctx                                ctx{};
+        std::array<audio_sample_t, kSamplesPerBuffer> playbackBuf;
+        bool                                          pendingReady = false;
+        std::size_t                                   frameCursor  = kFramesPerBuffer;
+        sdm_channel_handle_t                          sdmChannel   = nullptr;
+        gptimer_handle_t                              audioTimer   = nullptr;
+        bool                                          audioRunning = false;
+        int8_t                                        lastDensity  = 0;
+    };
+
     enum class Mode { Browse, Running };
     enum class ScaleMode { Original, FullHeight, FullHeightWide };
 
@@ -575,6 +922,11 @@ private:
     uint32_t             fpsCurrent        = 0;
     std::string          activeRomName;
     std::string          activeRomSavePath;
+    SimpleApu            apu{};
+    // Smoothing state for buzzer tone
+    uint32_t lastFreqHz   = 0;
+    uint8_t  lastLoud     = 0;
+    uint32_t stableFrames = 0;
 
     void cancelTick() {
         if (tickTimer != kInvalidAppTimer) {
@@ -760,6 +1112,11 @@ private:
 
         if (roms.empty())
             return;
+
+        if (input.b && !prevInput.b) {
+            context.requestAppSwitchByName(apps::kMenuAppName);
+            return;
+        }
         const auto wrapDecrement = [&]() {
             if (selectedIndex == 0)
                 selectedIndex = roms.size() - 1;
@@ -822,7 +1179,7 @@ private:
             }
 
             font16x8::drawText(framebuffer, 16, framebuffer.height() - 52, "A/START PLAY", 1, true, 1);
-            font16x8::drawText(framebuffer, 16, framebuffer.height() - 32, "SELECT RESCAN", 1, true, 1);
+            font16x8::drawText(framebuffer, 16, framebuffer.height() - 32, "B BACK   SELECT RESCAN", 1, true, 1);
         }
 
         if (!statusMessage.empty()) {
@@ -891,6 +1248,7 @@ private:
             return false;
         }
 
+        apu.reset();
         std::memset(&gb, 0, sizeof(gb));
         const auto initResult = gb_init(&gb, &GameboyApp::cartRamRead, &GameboyApp::cartRamWrite,
                                         &GameboyApp::errorCallback, this, romDataView);
@@ -927,6 +1285,8 @@ private:
         frameDirty    = true;
         activeRomName = rom.name.empty() ? "Game" : rom.name;
 
+        apu.startAudio();
+
         std::string statusText = "Running " + activeRomName;
         if (!fsReady)
             statusText.append(" (no save)");
@@ -943,12 +1303,15 @@ private:
             cartRam.clear();
             activeRomName.clear();
             activeRomSavePath.clear();
+            apu.stopAudio();
             return;
         }
 
         maybeSaveRam();
         resetFpsStats();
 
+        apu.stopAudio();
+
         gbReady = false;
         romData.clear();
         romDataView     = nullptr;
@@ -957,6 +1320,7 @@ private:
         activeRomName.clear();
         activeRomSavePath.clear();
         std::memset(&gb, 0, sizeof(gb));
+        apu.reset();
         mode         = Mode::Browse;
         browserDirty = true;
     }
@@ -1165,6 +1529,15 @@ private:
             setStatus("Partial save loaded");
         }
     }
+    static uint8_t audioReadThunk(void* ctx, uint16_t addr) {
+        auto* self = static_cast<GameboyApp*>(ctx);
+        return self ? self->audioReadRegister(addr) : 0xFF;
+    }
+
+    static void audioWriteThunk(void* ctx, uint16_t addr, uint8_t value) {
+        if (auto* self = static_cast<GameboyApp*>(ctx))
+            self->audioWriteRegister(addr, value);
+    }
 
     void setStatus(std::string message) {
         statusMessage = std::move(message);

Firmware/sdk/apps/menu/src/menu_app.cpp

@@ -47,7 +47,7 @@ public:
             moveSelection(+1);
         }
 
-        const bool launch = (current.a && !previous.a) || (current.select && !previous.select);
+        const bool launch = (current.a && !previous.a) || (current.start && !previous.start);
         if (launch)
             launchSelected();
 
@@ -153,7 +153,7 @@ private:
             font16x8::drawText(framebuffer, topRightX, 20, indexLabel, 1, true, 0);
 
             drawPagerDots();
-            drawCenteredText(framebuffer, framebuffer.height() - 48, "A/SELECT START", 1, 1);
+            drawCenteredText(framebuffer, framebuffer.height() - 48, "A START APP", 1, 1);
             drawCenteredText(framebuffer, framebuffer.height() - 28, "L/R CHOOSE", 1, 1);
         }
 
@@ -163,7 +163,7 @@ private:
 
 class MenuAppFactory final : public cardboy::sdk::IAppFactory {
 public:
-    const char*           name() const override { return kMenuAppName; }
+    const char*                         name() const override { return kMenuAppName; }
     std::unique_ptr<cardboy::sdk::IApp> create(cardboy::sdk::AppContext& context) override {
         return std::make_unique<MenuApp>(context);
     }

Firmware/sdk/apps/settings/src/settings_app.cpp

@@ -64,8 +64,8 @@ public:
             moved = true;
         }
 
-        const bool togglePressed = (current.a && !previous.a) || (current.select && !previous.select) ||
-                                   (current.start && !previous.start);
+        const bool togglePressed = (current.a && !previous.a) || (current.start && !previous.start) ||
+                                   (current.select && !previous.select);
         if (togglePressed)
             handleToggle();
 

Firmware/sdk/apps/tetris/src/tetris_app.cpp

@@ -185,8 +185,6 @@ private:
         state.paused       = false;
         dirty              = true;
         scheduleDropTimer();
-        if (auto* power = context.powerManager())
-            power->setSlowMode(false);
     }
 
     void handleButtons(const AppButtonEvent& evt) {
@@ -204,8 +202,6 @@ private:
                 reset();
             } else {
                 state.paused = !state.paused;
-                if (auto* power = context.powerManager())
-                    power->setSlowMode(state.paused);
             }
             dirty = true;
         }
@@ -387,8 +383,6 @@ private:
             cancelDropTimer();
             if (auto* buzzer = context.buzzer())
                 buzzer->beepGameOver();
-            if (auto* power = context.powerManager())
-                power->setSlowMode(true);
         } else {
             if (auto* buzzer = context.buzzer())
                 buzzer->beepLock();

Firmware/sdk/backend_interface/CMakeLists.txt

@@ -16,6 +16,8 @@ target_sources(cardboy_backend_interface
         ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/backend/backend_interface.hpp
         ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/sdk/backend.hpp
         ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/sdk/display_spec.hpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/sdk/event_bus.hpp
+        ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/sdk/loop_hooks.hpp
         ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/sdk/input_state.hpp
         ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/sdk/platform.hpp
         ${CMAKE_CURRENT_SOURCE_DIR}/include/cardboy/sdk/services.hpp

Firmware/sdk/backend_interface/include/cardboy/sdk/event_bus.hpp

@@ -0,0 +1,42 @@
+#pragma once
+
+#include <cstdint>
+
+namespace cardboy::sdk {
+
+enum class EventBusSignal : std::uint32_t {
+    None     = 0,
+    Input    = 1u << 0,
+    Timer    = 1u << 1,
+    External = 1u << 2,
+};
+
+inline EventBusSignal operator|(EventBusSignal lhs, EventBusSignal rhs) {
+    return static_cast<EventBusSignal>(static_cast<std::uint32_t>(lhs) | static_cast<std::uint32_t>(rhs));
+}
+
+inline EventBusSignal& operator|=(EventBusSignal& lhs, EventBusSignal rhs) {
+    lhs = lhs | rhs;
+    return lhs;
+}
+
+inline EventBusSignal operator&(EventBusSignal lhs, EventBusSignal rhs) {
+    return static_cast<EventBusSignal>(static_cast<std::uint32_t>(lhs) & static_cast<std::uint32_t>(rhs));
+}
+
+inline std::uint32_t to_event_bits(EventBusSignal signal) { return static_cast<std::uint32_t>(signal); }
+
+class IEventBus {
+public:
+    static constexpr std::uint32_t kWaitForever = 0xFFFFFFFFu;
+
+    virtual ~IEventBus() = default;
+
+    virtual void          signal(std::uint32_t bits)                         = 0;
+    virtual void          signalFromISR(std::uint32_t bits)                  = 0;
+    virtual std::uint32_t wait(std::uint32_t mask, std::uint32_t timeout_ms) = 0;
+    virtual void          scheduleTimerSignal(std::uint32_t delay_ms)        = 0;
+    virtual void          cancelTimerSignal()                                = 0;
+};
+
+} // namespace cardboy::sdk

Firmware/sdk/backend_interface/include/cardboy/sdk/loop_hooks.hpp

@@ -0,0 +1,11 @@
+#pragma once
+
+namespace cardboy::sdk {
+
+class ILoopHooks {
+public:
+    virtual ~ILoopHooks()          = default;
+    virtual void onLoopIteration() = 0;
+};
+
+} // namespace cardboy::sdk

Firmware/sdk/backend_interface/include/cardboy/sdk/services.hpp

@@ -1,5 +1,8 @@
 #pragma once
 
+#include "cardboy/sdk/event_bus.hpp"
+#include "cardboy/sdk/loop_hooks.hpp"
+
 #include <cstdint>
 #include <string>
 #include <string_view>
@@ -57,14 +60,6 @@ public:
     [[nodiscard]] virtual std::uint64_t micros() = 0;
 };
 
-class IPowerManager {
-public:
-    virtual ~IPowerManager() = default;
-
-    virtual void               setSlowMode(bool enable) = 0;
-    [[nodiscard]] virtual bool isSlowMode() const       = 0;
-};
-
 class IFilesystem {
 public:
     virtual ~IFilesystem() = default;
@@ -80,8 +75,9 @@ struct Services {
     IStorage*        storage      = nullptr;
     IRandom*         random       = nullptr;
     IHighResClock*   highResClock = nullptr;
-    IPowerManager*   powerManager = nullptr;
     IFilesystem*     filesystem   = nullptr;
+    IEventBus*       eventBus     = nullptr;
+    ILoopHooks*      loopHooks    = nullptr;
 };
 
 } // namespace cardboy::sdk

Firmware/sdk/backends/desktop/include/cardboy/backend/desktop_backend.hpp

@@ -1,14 +1,17 @@
 #pragma once
 
+#include "cardboy/sdk/event_bus.hpp"
 #include "cardboy/sdk/platform.hpp"
 #include "cardboy/sdk/services.hpp"
 
 #include <SFML/Graphics.hpp>
 #include <SFML/Window/Keyboard.hpp>
 #include <chrono>
+#include <condition_variable>
 #include <cstdint>
 #include <filesystem>
 #include <limits>
+#include <mutex>
 #include <random>
 #include <string>
 #include <string_view>
@@ -70,15 +73,6 @@ private:
     const std::chrono::steady_clock::time_point start;
 };
 
-class DesktopPowerManager final : public cardboy::sdk::IPowerManager {
-public:
-    void               setSlowMode(bool enable) override { slowMode = enable; }
-    [[nodiscard]] bool isSlowMode() const override { return slowMode; }
-
-private:
-    bool slowMode = false;
-};
-
 class DesktopFilesystem final : public cardboy::sdk::IFilesystem {
 public:
     DesktopFilesystem();
@@ -92,6 +86,29 @@ private:
     bool                  mounted = false;
 };
 
+class DesktopEventBus final : public cardboy::sdk::IEventBus {
+public:
+    explicit DesktopEventBus(DesktopRuntime& owner);
+    ~DesktopEventBus() override;
+
+    void          signal(std::uint32_t bits) override;
+    void          signalFromISR(std::uint32_t bits) override;
+    std::uint32_t wait(std::uint32_t mask, std::uint32_t timeout_ms) override;
+    void          scheduleTimerSignal(std::uint32_t delay_ms) override;
+    void          cancelTimerSignal() override;
+
+private:
+    DesktopRuntime&         runtime;
+    std::mutex              mutex;
+    std::condition_variable cv;
+    std::uint32_t           pendingBits = 0;
+
+    std::mutex              timerMutex;
+    std::condition_variable timerCv;
+    std::thread             timerThread;
+    bool                    timerCancel = false;
+};
+
 class DesktopFramebuffer final : public cardboy::sdk::FramebufferFacade<DesktopFramebuffer> {
 public:
     explicit DesktopFramebuffer(DesktopRuntime& runtime);
@@ -168,8 +185,8 @@ private:
     DesktopStorage         storageService;
     DesktopRandom          randomService;
     DesktopHighResClock    highResService;
-    DesktopPowerManager    powerService;
     DesktopFilesystem      filesystemService;
+    DesktopEventBus        eventBusService;
     cardboy::sdk::Services services{};
 };
 

Firmware/sdk/backends/desktop/src/desktop_backend.cpp

@@ -13,6 +13,92 @@
 
 namespace cardboy::backend::desktop {
 
+DesktopEventBus::DesktopEventBus(DesktopRuntime& owner) : runtime(owner) {}
+
+DesktopEventBus::~DesktopEventBus() { cancelTimerSignal(); }
+
+void DesktopEventBus::signal(std::uint32_t bits) {
+    if (bits == 0)
+        return;
+    {
+        std::lock_guard<std::mutex> lock(mutex);
+        pendingBits |= bits;
+    }
+    cv.notify_all();
+}
+
+void DesktopEventBus::signalFromISR(std::uint32_t bits) { signal(bits); }
+
+std::uint32_t DesktopEventBus::wait(std::uint32_t mask, std::uint32_t timeout_ms) {
+    if (mask == 0)
+        return 0;
+
+    const auto start    = std::chrono::steady_clock::now();
+    const bool infinite = timeout_ms == cardboy::sdk::IEventBus::kWaitForever;
+
+    while (true) {
+        {
+            std::lock_guard<std::mutex> lock(mutex);
+            const std::uint32_t         ready = pendingBits & mask;
+            if (ready != 0) {
+                pendingBits &= ~mask;
+                return ready;
+            }
+        }
+
+        if (!infinite) {
+            const auto now       = std::chrono::steady_clock::now();
+            const auto elapsedMs = std::chrono::duration_cast<std::chrono::milliseconds>(now - start).count();
+            if (elapsedMs >= static_cast<std::int64_t>(timeout_ms))
+                return 0;
+            const auto remaining = timeout_ms - static_cast<std::uint32_t>(elapsedMs);
+            runtime.sleepFor(std::min<std::uint32_t>(remaining, 8));
+        } else {
+            runtime.sleepFor(8);
+        }
+    }
+}
+
+void DesktopEventBus::scheduleTimerSignal(std::uint32_t delay_ms) {
+    cancelTimerSignal();
+
+    if (delay_ms == cardboy::sdk::IEventBus::kWaitForever)
+        return;
+
+    if (delay_ms == 0) {
+        signal(cardboy::sdk::to_event_bits(cardboy::sdk::EventBusSignal::Timer));
+        return;
+    }
+
+    {
+        std::lock_guard<std::mutex> lock(timerMutex);
+        timerCancel = false;
+    }
+
+    timerThread = std::thread([this, delay_ms]() {
+        std::unique_lock<std::mutex> lock(timerMutex);
+        const bool                   cancelled =
+                timerCv.wait_for(lock, std::chrono::milliseconds(delay_ms), [this] { return timerCancel; });
+        lock.unlock();
+        if (!cancelled)
+            signal(cardboy::sdk::to_event_bits(cardboy::sdk::EventBusSignal::Timer));
+    });
+}
+
+void DesktopEventBus::cancelTimerSignal() {
+    {
+        std::lock_guard<std::mutex> lock(timerMutex);
+        timerCancel = true;
+    }
+    timerCv.notify_all();
+    if (timerThread.joinable())
+        timerThread.join();
+    {
+        std::lock_guard<std::mutex> lock(timerMutex);
+        timerCancel = false;
+    }
+}
+
 bool DesktopStorage::readUint32(std::string_view ns, std::string_view key, std::uint32_t& out) {
     auto it = data.find(composeKey(ns, key));
     if (it == data.end())
@@ -90,6 +176,7 @@ DesktopInput::DesktopInput(DesktopRuntime& runtime) : runtime(runtime) {}
 cardboy::sdk::InputState DesktopInput::readState_impl() { return state; }
 
 void DesktopInput::handleKey(sf::Keyboard::Key key, bool pressed) {
+    bool handled = true;
     switch (key) {
         case sf::Keyboard::Key::Up:
             state.up = pressed;
@@ -118,8 +205,11 @@ void DesktopInput::handleKey(sf::Keyboard::Key key, bool pressed) {
             state.start = pressed;
             break;
         default:
+            handled = false;
             break;
     }
+    if (handled)
+        runtime.eventBusService.signal(cardboy::sdk::to_event_bits(cardboy::sdk::EventBusSignal::Input));
 }
 
 DesktopClock::DesktopClock(DesktopRuntime& runtime) : runtime(runtime), start(std::chrono::steady_clock::now()) {}
@@ -137,13 +227,13 @@ DesktopRuntime::DesktopRuntime() :
            "Cardboy Desktop"),
     texture(), sprite(texture),
     pixels(static_cast<std::size_t>(cardboy::sdk::kDisplayWidth * cardboy::sdk::kDisplayHeight) * 4, 0),
-    framebuffer(*this), input(*this), clock(*this) {
+    framebuffer(*this), input(*this), clock(*this), eventBusService(*this) {
     window.setFramerateLimit(60);
     if (!texture.resize(sf::Vector2u{cardboy::sdk::kDisplayWidth, cardboy::sdk::kDisplayHeight}))
         throw std::runtime_error("Failed to allocate texture for desktop framebuffer");
     sprite.setTexture(texture, true);
     sprite.setScale(sf::Vector2f{static_cast<float>(kPixelScale), static_cast<float>(kPixelScale)});
-    clearPixels(false);
+    clearPixels(true);
     presentIfNeeded();
 
     services.buzzer       = &buzzerService;
@@ -151,8 +241,9 @@ DesktopRuntime::DesktopRuntime() :
     services.storage      = &storageService;
     services.random       = &randomService;
     services.highResClock = &highResService;
-    services.powerManager = &powerService;
     services.filesystem   = &filesystemService;
+    services.eventBus     = &eventBusService;
+    services.loopHooks    = nullptr;
 }
 
 cardboy::sdk::Services& DesktopRuntime::serviceRegistry() { return services; }
@@ -161,7 +252,7 @@ void DesktopRuntime::setPixel(int x, int y, bool on) {
     if (x < 0 || y < 0 || x >= cardboy::sdk::kDisplayWidth || y >= cardboy::sdk::kDisplayHeight)
         return;
     const std::size_t  idx   = static_cast<std::size_t>(y * cardboy::sdk::kDisplayWidth + x) * 4;
-    const std::uint8_t value = on ? static_cast<std::uint8_t>(255) : static_cast<std::uint8_t>(0);
+    const std::uint8_t value = on ? static_cast<std::uint8_t>(0) : static_cast<std::uint8_t>(255);
     pixels[idx + 0]          = value;
     pixels[idx + 1]          = value;
     pixels[idx + 2]          = value;
@@ -170,7 +261,7 @@ void DesktopRuntime::setPixel(int x, int y, bool on) {
 }
 
 void DesktopRuntime::clearPixels(bool on) {
-    const std::uint8_t value = on ? static_cast<std::uint8_t>(255) : static_cast<std::uint8_t>(0);
+    const std::uint8_t value = on ? static_cast<std::uint8_t>(0) : static_cast<std::uint8_t>(255);
     for (std::size_t i = 0; i < pixels.size(); i += 4) {
         pixels[i + 0] = value;
         pixels[i + 1] = value;

Firmware/sdk/core/include/cardboy/sdk/app_framework.hpp

@@ -61,8 +61,9 @@ struct AppContext {
     [[nodiscard]] IStorage*        storage() const { return services ? services->storage : nullptr; }
     [[nodiscard]] IRandom*         random() const { return services ? services->random : nullptr; }
     [[nodiscard]] IHighResClock*   highResClock() const { return services ? services->highResClock : nullptr; }
-    [[nodiscard]] IPowerManager*   powerManager() const { return services ? services->powerManager : nullptr; }
     [[nodiscard]] IFilesystem*     filesystem() const { return services ? services->filesystem : nullptr; }
+    [[nodiscard]] IEventBus*       eventBus() const { return services ? services->eventBus : nullptr; }
+    [[nodiscard]] ILoopHooks*      loopHooks() const { return services ? services->loopHooks : nullptr; }
 
     void requestAppSwitchByIndex(std::size_t index) {
         pendingAppIndex = index;

Firmware/sdk/core/include/cardboy/sdk/app_system.hpp

@@ -1,5 +1,6 @@
 #pragma once
 
+#include <cardboy/sdk/event_bus.hpp>
 #include "app_framework.hpp"
 
 #include <cstdint>
@@ -51,6 +52,7 @@ private:
     void          clearTimersForCurrentApp();
     TimerRecord*  findTimer(AppTimerHandle handle);
     bool          handlePendingSwitchRequest();
+    void          notifyEventBus(EventBusSignal signal);
 
     AppContext                                context;
     std::vector<std::unique_ptr<IAppFactory>> factories;
@@ -61,6 +63,7 @@ private:
     AppTimerHandle                            nextTimerId       = 1;
     std::uint32_t                             currentGeneration = 0;
     InputState                                lastInputState{};
+    bool                                      suppressInputs = false;
 };
 
 inline AppTimerHandle AppContext::scheduleTimerInternal(std::uint32_t delay_ms, bool repeat) {

Firmware/sdk/core/src/app_system.cpp

@@ -13,7 +13,9 @@ namespace {
            a.select != b.select || a.start != b.start;
 }
 
-constexpr std::uint32_t kIdlePollMs = 16;
+[[nodiscard]] bool anyButtonPressed(const InputState& state) {
+    return state.up || state.down || state.left || state.right || state.a || state.b || state.select || state.start;
+}
 
 template<typename Framebuffer>
 void statusBarPreSendHook(void* framebuffer, void* userData) {
@@ -71,6 +73,7 @@ bool AppSystem::startAppByIndex(std::size_t index) {
     clearTimersForCurrentApp();
     current        = std::move(app);
     lastInputState = context.input.readState();
+    suppressInputs = true;
     StatusBar::instance().setServices(context.services);
     StatusBar::instance().setCurrentAppName(activeFactory ? activeFactory->name() : "");
     current->onStart();
@@ -87,6 +90,9 @@ void AppSystem::run() {
     events.reserve(4);
 
     while (true) {
+        if (auto* hooks = context.loopHooks())
+            hooks->onLoopIteration();
+
         events.clear();
         const std::uint32_t now = context.clock.millis();
         processDueTimers(now, events);
@@ -94,7 +100,11 @@ void AppSystem::run() {
         const InputState inputNow               = context.input.readState();
         const bool       consumedByStatusToggle = StatusBar::instance().handleToggleInput(inputNow, lastInputState);
 
-        if (!consumedByStatusToggle && inputsDiffer(inputNow, lastInputState)) {
+        if (suppressInputs) {
+            lastInputState = inputNow;
+            if (!anyButtonPressed(inputNow))
+                suppressInputs = false;
+        } else if (!consumedByStatusToggle && inputsDiffer(inputNow, lastInputState)) {
             AppEvent evt{};
             evt.type            = AppEventType::Button;
             evt.timestamp_ms    = now;
@@ -118,13 +128,19 @@ void AppSystem::run() {
         if (waitMs == 0)
             continue;
 
-        if (waitMs == std::numeric_limits<std::uint32_t>::max())
-            waitMs = kIdlePollMs;
-        else
-            waitMs = std::min(waitMs, kIdlePollMs);
+        auto* eventBus = context.eventBus();
+        if (!eventBus)
+            return;
 
-        if (waitMs > 0)
-            context.clock.sleep_ms(waitMs);
+        const std::uint32_t mask = to_event_bits(EventBusSignal::Input) | to_event_bits(EventBusSignal::Timer);
+
+        if (waitMs == std::numeric_limits<std::uint32_t>::max()) {
+            eventBus->cancelTimerSignal();
+            eventBus->wait(mask, IEventBus::kWaitForever);
+        } else {
+            eventBus->scheduleTimerSignal(waitMs);
+            eventBus->wait(mask, IEventBus::kWaitForever);
+        }
     }
 }
 
@@ -158,24 +174,32 @@ AppTimerHandle AppSystem::scheduleTimer(std::uint32_t delay_ms, bool repeat) {
     record.repeat      = repeat;
     record.active      = true;
     timers.push_back(record);
+    notifyEventBus(EventBusSignal::Timer);
     return record.id;
 }
 
 void AppSystem::cancelTimer(AppTimerHandle handle) {
     auto* timer = findTimer(handle);
-    if (timer)
-        timer->active = false;
+    if (!timer)
+        return;
+    timer->active = false;
     timers.erase(std::remove_if(timers.begin(), timers.end(), [](const TimerRecord& rec) { return !rec.active; }),
                  timers.end());
+    notifyEventBus(EventBusSignal::Timer);
 }
 
 void AppSystem::cancelAllTimers() {
+    bool changed = false;
     for (auto& timer: timers) {
-        if (timer.generation == currentGeneration)
+        if (timer.generation == currentGeneration && timer.active) {
             timer.active = false;
+            changed      = true;
+        }
     }
     timers.erase(std::remove_if(timers.begin(), timers.end(), [](const TimerRecord& rec) { return !rec.active; }),
                  timers.end());
+    if (changed)
+        notifyEventBus(EventBusSignal::Timer);
 }
 
 void AppSystem::dispatchEvent(const AppEvent& event) {
@@ -220,8 +244,11 @@ std::uint32_t AppSystem::nextTimerDueMs(std::uint32_t now) const {
 }
 
 void AppSystem::clearTimersForCurrentApp() {
+    const bool hadTimers = !timers.empty();
     ++currentGeneration;
     timers.clear();
+    if (hadTimers)
+        notifyEventBus(EventBusSignal::Timer);
 }
 
 AppSystem::TimerRecord* AppSystem::findTimer(AppTimerHandle handle) {
@@ -251,4 +278,11 @@ bool AppSystem::handlePendingSwitchRequest() {
     return switched;
 }
 
+void AppSystem::notifyEventBus(EventBusSignal signal) {
+    if (signal == EventBusSignal::None)
+        return;
+    if (auto* bus = context.eventBus())
+        bus->signal(to_event_bits(signal));
+}
+
 } // namespace cardboy::sdk

Firmware/sdk/core/src/status_bar.cpp

@@ -63,12 +63,6 @@ std::string StatusBar::prepareRightText() const {
         right.assign(buf);
     }
 
-    if (services_->powerManager && services_->powerManager->isSlowMode()) {
-        if (!right.empty())
-            right.append(" ");
-        right.append("SLOW");
-    }
-
     if (services_->buzzer && services_->buzzer->isMuted()) {
         if (!right.empty())
             right.append(" ");