Refactor ownership of draw buffer data.

esp/cpp/06_i2c-scanner/main/idf_component.yml

@@ -2,7 +2,7 @@
 dependencies:
   ## Required IDF version
   idf:
-    version: '>=4.1.0'
+    version: '>=5.3.0'
   # # Put list of dependencies here
   # # For components maintained by Espressif:
   # component: "~1.0.0"

esp/cpp/06_i2c-scanner/sdkconfig

@@ -2091,6 +2091,15 @@ CONFIG_MDNS_TASK_STACK_SIZE=4096
 CONFIG_MDNS_TASK_AFFINITY_CPU0=y
 # CONFIG_MDNS_TASK_AFFINITY_CPU1 is not set
 CONFIG_MDNS_TASK_AFFINITY=0x0
+
+#
+# MDNS Memory Configuration
+#
+CONFIG_MDNS_TASK_CREATE_FROM_INTERNAL=y
+CONFIG_MDNS_MEMORY_ALLOC_INTERNAL=y
+# CONFIG_MDNS_MEMORY_CUSTOM_IMPL is not set
+# end of MDNS Memory Configuration
+
 CONFIG_MDNS_SERVICE_ADD_TIMEOUT_MS=2000
 CONFIG_MDNS_TIMER_PERIOD_MS=100
 # CONFIG_MDNS_NETWORKING_SOCKET is not set

esp/cpp/07_lcd-panel-i2c/README.md

@@ -12,8 +12,6 @@ For instructions on setting up the ESP-IDF see [04_-esp-idf-arduino](./../04_esp
 
 ![schematic](./schematic.png)
 
-Temperature and humidity sensor served on a web page within the local network.
-
 ![example](./example.gif)
 
 To build this example run the following commands.

esp/cpp/07_lcd-panel-i2c/main/CMakeLists.txt

@@ -1,5 +1,7 @@
 idf_component_register(
-    SRCS main.cpp display.cpp ssd1306.cpp i2c.h time_keeper.h panel.h panel_device.h
+    SRCS
+    main.cpp display.cpp panel_device.cpp scoped_lock.cpp
+    i2c.h time_keeper.h panel.h ssd1306.h
     INCLUDE_DIRS .
     REQUIRES driver
 )

esp/cpp/07_lcd-panel-i2c/main/display.cpp

@@ -10,19 +10,11 @@
 // TODO: Remove this dependency by relocating SSD1306::oledb_buffer_
 #include "ssd1306.h"
 
-// LVGL library is not thread-safe, this example calls LVGL APIs from tasks.
-// We must use a mutex to protect it.
-_lock_t Display::ScopedLock::lv_lock_;
-
 // Static TimeKeeper for managing ESP timers across all displays.
 TimeKeeper Display::timers_;
 
-/// Tag used for ESP logging.
-const char * TAG = "Display";
-
 Display::Display(IPanelDevice &device) :
-    panel_(device),
+    panel_(device)
-    lv_buf_(nullptr)
 {
   if (!lv_is_initialized()) {
     ESP_LOGI(TAG, "Initialize LVGL");
@@ -34,12 +26,7 @@ Display::Display(IPanelDevice &device) :
   // associate the i2c panel handle to the display
   lv_display_set_user_data(lv_display_, panel_.esp_panel_);
 
-  register_draw_buffer();
+  panel_.register_display_callbacks(lv_display_);
-  register_lvgl_tick_timer();
-
-  ESP_LOGI(TAG, "Create LVGL FreeRTOS task");
-  xTaskCreate(Display::lvgl_port_task, "LVGL", LVGL_TASK_STACK_SIZE,
-              nullptr, LVGL_TASK_PRIORITY, nullptr);
 }
 
 void Display::set_text(const char *text,
@@ -68,110 +55,3 @@ void Display::set_text(const char *text,
   lv_obj_set_width(obj, lv_display_get_horizontal_resolution(lv_display_));
   lv_obj_align(obj, align, 0, 0);
 }
-
-bool Display::lvgl_flush_ready_cb(esp_lcd_panel_io_handle_t,
-                                  esp_lcd_panel_io_event_data_t *,
-                                  void *user_ctx)
-{
-  auto *disp = (lv_display_t *) user_ctx;
-  lv_display_flush_ready(disp);
-  return false;
-}
-
-void Display::lvgl_flush_cb(lv_display_t *display, const lv_area_t *area,
-                            uint8_t *px_map) // NOLINT(*-non-const-parameter)
-{
-  auto panel_handle =
-      (esp_lcd_panel_handle_t) lv_display_get_user_data(display);
-
-  // Necessary because LVGL reserves 2x4 bytes in the buffer for a palette.
-  // For more information about the monochrome, please refer to:
-  // https://docs.lvgl.io/9.2/porting/display.html#monochrome-displays
-  // Skip the palette here.
-  px_map += LVGL_PALETTE_SIZE;
-
-  uint16_t hor_res = lv_display_get_physical_horizontal_resolution(display);
-  int32_t x1 = area->x1;
-  int32_t x2 = area->x2;
-  int32_t y1 = area->y1;
-  int32_t y2 = area->y2;
-
-  for (int32_t y = y1; y <= y2; y++) {
-    for (int32_t x = x1; x <= x2; x++) {
-      /* The order of bits is MSB first.
-                  MSB           LSB
-         bits      7 6 5 4 3 2 1 0
-         pixels    0 1 2 3 4 5 6 7
-                  Left         Right
-      */
-      bool chroma_color = (px_map[(hor_res >> 3) * y + (x >> 3)] &
-                           1 << (7 - x % 8));
-
-      // Write to the buffer as required for the display.
-      // It writes only 1-bit for monochrome displays mapped vertically.
-      uint8_t *buf = SSD1306::oled_buffer_ + hor_res * (y >> 3) + (x);
-      if (chroma_color) {
-        (*buf) &= ~(1 << (y % 8));
-      } else {
-        (*buf) |= (1 << (y % 8));
-      }
-    }
-  }
-  // Pass the draw buffer to the driver.
-  ESP_ERROR_CHECK(
-      esp_lcd_panel_draw_bitmap(panel_handle, x1, y1, x2 + 1, y2 + 1,
-                                SSD1306::oled_buffer_));
-}
-
-void Display::lvgl_increase_tick_cb(void *)
-{
-  // Tell LVGL how many milliseconds has elapsed
-  lv_tick_inc(LVGL_TICK_PERIOD_MS);
-}
-
-[[noreturn]] void Display::lvgl_port_task(void *)
-{
-  ESP_LOGI(TAG, "Starting LVGL task");
-  for (uint32_t time_to_next_ms = 0; true; usleep(1000 * time_to_next_ms)) {
-    ScopedLock lock;
-    time_to_next_ms = lv_timer_handler();
-  }
-}
-
-void Display::register_draw_buffer()
-{
-  // Create draw buffer.
-  ESP_LOGI(TAG, "Allocate separate LVGL draw buffers");
-  lv_buf_ = heap_caps_calloc(1, panel_.device_->lv_buf_size_,
-                             MALLOC_CAP_INTERNAL | MALLOC_CAP_8BIT);
-  assert(lv_buf_);
-
-  ESP_LOGI(TAG, "Set LVGL draw buffers");
-  // Color format must be set first, LVGL9 suooprt new monochromatic format.
-  lv_display_set_color_format(lv_display_, LV_COLOR_FORMAT_I1);
-  lv_display_set_buffers(lv_display_, lv_buf_, nullptr,
-                         panel_.device_->lv_buf_size_,
-                         LV_DISPLAY_RENDER_MODE_FULL);
-  lv_display_set_rotation(lv_display_, LV_DISPLAY_ROTATION_0);
-
-  ESP_LOGI(TAG, "Set LVGL callback for flushing to the display");
-  lv_display_set_flush_cb(lv_display_, Display::lvgl_flush_cb);
-
-  ESP_LOGI(TAG, "Register io panel callback for LVGL flush ready notification");
-  const esp_lcd_panel_io_callbacks_t cbs = {
-      .on_color_trans_done = Display::lvgl_flush_ready_cb,
-  };
-  ESP_ERROR_CHECK(
-      esp_lcd_panel_io_register_event_callbacks(panel_.esp_io_, &cbs,
-                                                lv_display_));
-}
-
-void Display::register_lvgl_tick_timer()
-{
-  ESP_LOGI(TAG, "Use esp_timer to increase LVGL tick");
-  const esp_timer_create_args_t esp_timer_args = {
-      .callback = &Display::lvgl_increase_tick_cb,
-      .name = "lvgl_tick"
-  };
-  timers_.start_new_timer_periodic(esp_timer_args, LVGL_TICK_PERIOD_MS * 1000);
-}

esp/cpp/07_lcd-panel-i2c/main/display.h

@@ -1,17 +1,13 @@
 #ifndef DISPLAY_H
 #define DISPLAY_H
 
-
 #include <widgets/label/lv_label.h>
 
 #include <unordered_map>
 
 #include "time_keeper.h"
 #include "panel.h"
-
+#include "scoped_lock.h"
-#define LVGL_TICK_PERIOD_MS    5
-#define LVGL_TASK_STACK_SIZE   (4 * 1024)
-#define LVGL_TASK_PRIORITY     2
 
 /**
  * Encapsulates lv_display handle and related LVGL operations.
@@ -37,6 +33,8 @@ public:
 
   Display &operator=(Display &) = delete;
 
+  using lv_display_handle_t = lv_display_t *;
+
   //
   // GETTERS
 
@@ -45,20 +43,20 @@ public:
    *
    * @sa ScopedLock for calling custom LVGL API's not implemented by Display.
    */
-  [[nodiscard]] inline const lv_display_t *get() const { return lv_display_; }
+  [[nodiscard]] inline lv_display_handle_t get() const { return lv_display_; }
 
   /**
    * Getter for accessing LVGL display handle.
    *
    * @sa ScopedLock for calling custom LVGL API's not implemented by Display.
    */
-  [[nodiscard]] inline lv_display_t *get() { return lv_display_; }
+  [[nodiscard]] inline lv_display_handle_t get() { return lv_display_; }
 
   /// Dereference operator for accessing LVGL display handle.
-  [[nodiscard]] inline const lv_display_t *operator*() const { return get(); }
+  [[nodiscard]] inline lv_display_handle_t operator*() const { return get(); }
 
   /// Dereference operator for accessing LVGL display handle.
-  [[nodiscard]] inline lv_display_t *operator*() { return get(); }
+  [[nodiscard]] inline lv_display_handle_t operator*() { return get(); }
 
   //
   // LVGL OPERATIONS
@@ -77,24 +75,6 @@ public:
                 lv_label_long_mode_t long_mode = LV_LABEL_LONG_SCROLL_CIRCULAR,
                 lv_align_t align = LV_ALIGN_TOP_MID);
 
-  //
-  // TYPE DEFINITIONS
-
-  /**
-   * Obtains LVGL API mutex lock for the duration of local scope.
-   *
-   * LVGL library is not thread-safe, this lock should be held when making calls
-   * to the LVGL API, and released as soon as possible when finished.
-   */
-  struct ScopedLock {
-    explicit ScopedLock() { _lock_acquire(&lv_lock_); }
-
-    ~ScopedLock() { _lock_release(&lv_lock_); }
-
-    /// Mutex used to protect LVGL API calls.
-    static _lock_t lv_lock_;
-  };
-
   //
   // PUBLIC STATIC MEMBERS
 
@@ -103,30 +83,6 @@ public:
 
 private:
 
-  //
-  // PRIVATE METHODS
-
-  /// Registers LVGL draw buffers for this display.
-  void register_draw_buffer();
-
-  //
-  // PRIVATE STATIC METHODS
-
-  /// Registers LVGL ticker timer callback for rendering this display.
-  static void register_lvgl_tick_timer();
-
-  static bool lvgl_flush_ready_cb(esp_lcd_panel_io_handle_t panel,
-                                  esp_lcd_panel_io_event_data_t *data,
-                                  void *user_ctx);
-
-  static void lvgl_flush_cb(lv_display_t *display,
-                            const lv_area_t *area,
-                            uint8_t *px_map);
-
-  static void lvgl_increase_tick_cb(void *arg);
-
-  [[noreturn]] static void lvgl_port_task(void *arg);
-
   //
   // PRIVATE MEMBERS
 
@@ -134,10 +90,7 @@ private:
   Panel panel_;
 
   /// LVGL display handle.
-  lv_display_t *lv_display_;
+  lv_display_handle_t lv_display_;
-
-  /// LVGL draw buffer associated with this Display's lv_display_t.
-  void *lv_buf_;
 
   /**
    * LVGL object handles stored in the LVGL screen associated with this Display.
@@ -146,6 +99,9 @@ private:
    * @sa lv_display_get_screen_active
    */
   std::unordered_map<const char *, lv_obj_t *> lv_objects_;
+
+  /// Tag used for ESP logging.
+  constexpr static const char *TAG = "Display";
 };
 
 #endif // DISPLAY_H

esp/cpp/07_lcd-panel-i2c/main/i2c.h

@@ -78,7 +78,7 @@ private:
   // PRIVATE MEMBERS
 
   /// Tag used for ESP logging.
-  const char * TAG = "I2C";
+  constexpr static const char *TAG = "I2C";
 };
 
 #endif //I2C_H

esp/cpp/07_lcd-panel-i2c/main/panel.h

@@ -57,13 +57,24 @@ struct Panel {
   /// ESP LCD panel configuration structure.
   esp_lcd_panel_dev_config_t esp_panel_config_;
 
+  /**
+   * Registers LVGL draw buffers and callbacks for rendering the display.
+   *
+   * @param display_handle Pointer to the LVGL display to use for rendering.
+   */
+  inline void register_display_callbacks(lv_display_t *display_handle) const
+  {
+    device_->register_draw_buffer(display_handle, esp_io_);
+    device_->register_lvgl_tick_timer();
+  }
+
 private:
 
   //
   // PRIVATE MEMBERS
 
   /// Tag used for ESP logging.
-  const char * TAG = "Panel";
+  constexpr static const char *TAG = "Panel";
 };
 
 #endif //PANEL_H

esp/cpp/07_lcd-panel-i2c/main/panel_device.cpp

@@ -0,0 +1,135 @@
+
+#include "panel_device.h"
+#include "display.h"
+#include "scoped_lock.h"
+#include "time_keeper.h"
+
+// To use LV_COLOR_FORMAT_I1 we need an extra buffer to hold the converted data.
+uint8_t IPanelDevice::oled_buffer_[LCD_H_RES * LCD_V_RES / 8];
+
+bool IPanelDevice::lvgl_flush_ready_cb(esp_lcd_panel_io_handle_t,
+                                       esp_lcd_panel_io_event_data_t *,
+                                       void *user_ctx)
+{
+  auto *disp = (lv_display_t *) user_ctx;
+  lv_display_flush_ready(disp);
+  return false;
+}
+
+void IPanelDevice::lvgl_flush_cb(lv_display_t *display, const lv_area_t *area,
+                                 uint8_t *px_map) // NOLINT(*-non-const-parameter)
+{
+  auto panel_handle =
+      (esp_lcd_panel_handle_t) lv_display_get_user_data(display);
+
+  // Necessary because LVGL reserves 2x4 bytes in the buffer for a palette.
+  // For more information about the monochrome, please refer to:
+  // https://docs.lvgl.io/9.2/porting/display.html#monochrome-displays
+  // Skip the palette here.
+  px_map += LVGL_PALETTE_SIZE;
+
+  uint16_t hor_res = lv_display_get_physical_horizontal_resolution(display);
+  int32_t x1 = area->x1;
+  int32_t x2 = area->x2;
+  int32_t y1 = area->y1;
+  int32_t y2 = area->y2;
+
+  for (int32_t y = y1; y <= y2; y++) {
+    for (int32_t x = x1; x <= x2; x++) {
+      /* The order of bits is MSB first.
+                  MSB           LSB
+         bits      7 6 5 4 3 2 1 0
+         pixels    0 1 2 3 4 5 6 7
+                  Left         Right
+      */
+      bool chroma_color = (px_map[(hor_res >> 3) * y + (x >> 3)] &
+                           1 << (7 - x % 8));
+
+      // Write to the buffer as required for the display.
+      // It writes only 1-bit for monochrome displays mapped vertically.
+      uint8_t *buf = IPanelDevice::oled_buffer_ + hor_res * (y >> 3) + (x);
+      if (chroma_color) {
+        (*buf) &= ~(1 << (y % 8));
+      } else {
+        (*buf) |= (1 << (y % 8));
+      }
+    }
+  }
+  // Pass the draw buffer to the driver.
+  ESP_ERROR_CHECK(
+      esp_lcd_panel_draw_bitmap(panel_handle, x1, y1, x2 + 1, y2 + 1,
+                                IPanelDevice::oled_buffer_));
+}
+
+void IPanelDevice::lvgl_increase_tick_cb(void *)
+{
+  // Tell LVGL how many milliseconds has elapsed
+  lv_tick_inc(LVGL_TICK_PERIOD_MS);
+}
+
+[[noreturn]] void IPanelDevice::lvgl_port_task(void *)
+{
+  // Optionally initialize some LVGL objects here before entering loop below.
+
+  ESP_LOGI(TAG, "Starting LVGL task");
+  for (uint32_t time_to_next_ms = 0; true; usleep(1000 * time_to_next_ms)) {
+    // Obtain LVGL API lock before calling any LVGL methods.
+    ScopedLock lock;
+
+    // Optionally handle LVGL input or event logic here.
+
+    // Update LVGL periodic timers.
+    time_to_next_ms = lv_timer_handler();
+  }
+}
+
+void IPanelDevice::register_draw_buffer(lv_display_t *display_handle,
+                                        esp_lcd_panel_io_handle_t io_handle)
+{
+  // Create draw buffer.
+  ESP_LOGI(TAG, "Allocate separate LVGL draw buffers");
+  lv_buf_ = heap_caps_calloc(1, lv_buf_size_,
+                             MALLOC_CAP_INTERNAL | MALLOC_CAP_8BIT);
+  assert(lv_buf_);
+
+  ESP_LOGI(TAG, "Set LVGL draw buffers");
+  // Color format must be set first, LVGL9 suooprt new monochromatic format.
+  lv_display_set_color_format(display_handle, LV_COLOR_FORMAT_I1);
+  lv_display_set_buffers(display_handle, lv_buf_, nullptr,
+                         lv_buf_size_,
+                         LV_DISPLAY_RENDER_MODE_FULL);
+  lv_display_set_rotation(display_handle, LV_DISPLAY_ROTATION_0);
+
+  ESP_LOGI(TAG, "Set LVGL callback for flushing to the display");
+  lv_display_set_flush_cb(display_handle, IPanelDevice::lvgl_flush_cb);
+
+  ESP_LOGI(TAG, "Register io panel callback for LVGL flush ready notification");
+  const esp_lcd_panel_io_callbacks_t cbs = {
+      .on_color_trans_done = IPanelDevice::lvgl_flush_ready_cb,
+  };
+  ESP_ERROR_CHECK(
+      esp_lcd_panel_io_register_event_callbacks(io_handle, &cbs,
+                                                display_handle));
+}
+
+void IPanelDevice::register_lvgl_tick_timer()
+{
+  ESP_LOGI(TAG, "Use esp_timer to increase LVGL tick");
+  const esp_timer_create_args_t esp_timer_args = {
+      .callback = &IPanelDevice::lvgl_increase_tick_cb,
+      // Data to pass to the IPanelDevice::lvgl_port_task callback.
+      .arg = nullptr,
+      .name = "lvgl_tick",
+  };
+  Display::timers_.start_new_timer_periodic(esp_timer_args,
+                                            LVGL_TICK_PERIOD_MS * 1000);
+
+  // LVGL requires a FreeRTOS task for running it's event loop.
+  // The lvgl_port_task callback can update the UI or handle input logic.
+  // For this basic example we don't do either of these things.
+  ESP_LOGI(TAG, "Create LVGL FreeRTOS task");
+  // Optionally set user data to pass to LVGL's FreeRTOS task callback here.
+  void *user_data = nullptr;
+  xTaskCreate(lvgl_port_task, "LVGL", LVGL_TASK_STACK_SIZE,
+              user_data, LVGL_TASK_PRIORITY, nullptr);
+}

esp/cpp/07_lcd-panel-i2c/main/panel_device.h

@@ -13,6 +13,12 @@
 // LVGL reserves 2x4 bytes in the buffer to be used as a palette.
 // This additional space must be added to the IPanelDevice::buf_size_.
 #define LVGL_PALETTE_SIZE      8
+#define LVGL_TICK_PERIOD_MS    5
+#define LVGL_TASK_STACK_SIZE   (4 * 1024)
+#define LVGL_TASK_PRIORITY     2
+
+#define LCD_H_RES              128
+#define LCD_V_RES              64
 
 /**
  * Encapsulates vendor specific ESP LCD panel initialization logic.
@@ -139,28 +145,116 @@ public:
   /// ESP LCD panel IO configuration.
   esp_lcd_panel_io_i2c_config_t esp_io_config_;
 
+  /**
+   * Registers LVGL draw buffers for this display.
+   *
+   * An implementation of the interface can optionally override this method to
+   * provide custom LVGL callbacks and display configurations.
+   *
+   * @param display_handle LVGL display handle to use for rendering.
+   * @param io_handle IO handle for the ESP LCD panel.
+   */
+  virtual void register_draw_buffer(lv_display_t *display_handle,
+                                    esp_lcd_panel_io_handle_t io_handle);
+
+  /**
+   * Registers LVGL ticker timer callback for rendering this display.
+   *
+   * An implementation of the interface can optionally override this method to
+   * provide custom LVGL callbacks and tick configurations.
+   */
+  virtual void register_lvgl_tick_timer();
+
 private:
 
   //
   // PRIVATE METHODS
 
   /**
-   * Initializes the ESP panel using vendor specific APIs and configurations.
+    * Initializes the ESP panel using vendor specific APIs and configurations.
-   * This method should implement any setup logic specific to the device.
+    * This method should implement any setup logic specific to the device.
-   *
+    *
-   * @param config ESP LCD panel configuration.
+    * @param config ESP LCD panel configuration.
-   * @param io ESP LCD panel IO handle.
+    * @param io ESP LCD panel IO handle.
-   * @param [out] panel ESP LCD panel handle output pointer location.
+    * @param [out] panel ESP LCD panel handle output pointer location.
-   */
+    */
   virtual void init_panel(esp_lcd_panel_dev_config_t &config,
                           esp_lcd_panel_io_handle_t io,
                           esp_lcd_panel_handle_t &panel) = 0;
 
+  //
+  // PRIVATE STATIC METHODS
+
+/**
+ * The callback invoked when panel IO finishes transferring color data.
+ * This signals that the panel is ready to flush image data to the display.
+ *
+ * @param panel LCD panel IO handles.
+ * @param data Panel IO event data, fed by driver.
+ * @param user_ctx User data, passed from `esp_lcd_panel_io_xxx_config_t`.
+ * @return Whether a high priority task has been waken up by this function.
+ * @sa SSD1306::SSD1306 for setting user_ctx data passed to the callback.
+ * @sa register_rendering_data for overriding this callback.
+ */
+  static bool lvgl_flush_ready_cb(esp_lcd_panel_io_handle_t panel,
+                                  esp_lcd_panel_io_event_data_t *data,
+                                  void *user_ctx);
+
+  /**
+   * The callback invoked for flushing the rendered image to the display.
+   *
+   * `px_map` contains the rendered image as raw pixel map and it should be
+   *  copied to `area` on the display.
+   *
+   * @param display LVGL display handle to use for rendering.
+   * @param area Area of the display being flushed.
+   * @param px_map Rendered image data for writing to the display area.
+   * @sa register_rendering_data for overriding this callback.
+   */
+  static void lvgl_flush_cb(lv_display_t *display,
+                            const lv_area_t *area,
+                            uint8_t *px_map);
+
+  /**
+   * Callback invoked for every period of the timer.
+   *
+   * This callback _must_ call lv_tick_inc to inform LVGL how much time has
+   * elapsed since the last period of the timer.
+   *
+   * @param data User data passed to the callback.
+   * @sa register_lvgl_tick_timer for setting user data and the tick period of
+   *        the timer, or overriding this callback entirely.
+   */
+  static void lvgl_increase_tick_cb(void *data);
+
+  /**
+   * FreeRTOS task callback invoked for handling LVGL events or updating the UI.
+   *
+   * This function is intentionally an endless loop and should never return.
+   * LVGL initialization logic can optionally be added before entering the loop.
+   * Input logic can optionally be handled within the loop.
+   *
+   * This callback _must_ call lv_timer_handler to handle LVGL periodic timers.
+   *
+   * @param data User data passed to the callback.
+   * @sa register_lvgl_tick_timer for overriding this callback.
+   */
+  [[noreturn]] static void lvgl_port_task(void *data);
+
+  /**
+   * Draw buffer for this panel device.
+   * For LV_COLOR_FORMAT_I1 we need an extra buffer to hold the converted data.
+   */
+  static uint8_t oled_buffer_[LCD_H_RES * LCD_V_RES / 8];
+
   //
   // PRIVATE MEMBERS
 
+  /// LVGL draw buffer associated with this Display's lv_display_t.
+  void *lv_buf_;
+
   /// Tag used for ESP logging.
-  const char * TAG = "IPanelDevice";
+  constexpr static const char *TAG = "IPanelDevice";
 };
 
 #endif // PANEL_DEVICE_H

esp/cpp/07_lcd-panel-i2c/main/scoped_lock.cpp

@@ -0,0 +1,5 @@
+#include "scoped_lock.h"
+
+// LVGL library is not thread-safe, this example calls LVGL APIs from tasks.
+// We must use a mutex to protect it.
+_lock_t ScopedLock::lv_lock_;

esp/cpp/07_lcd-panel-i2c/main/scoped_lock.h

@@ -0,0 +1,21 @@
+#ifndef SCOPED_LOCK_H
+#define SCOPED_LOCK_H
+
+#include <mutex>
+
+/**
+ * Obtains LVGL API mutex lock for the duration of local scope.
+ *
+ * LVGL library is not thread-safe, this lock should be held when making calls
+ * to the LVGL API, and released as soon as possible when finished.
+ */
+struct ScopedLock {
+  explicit ScopedLock() { _lock_acquire(&lv_lock_); }
+
+  ~ScopedLock() { _lock_release(&lv_lock_); }
+
+  /// Mutex used to protect LVGL API calls.
+  static _lock_t lv_lock_;
+};
+
+#endif // SCOPED_LOCK_H

esp/cpp/07_lcd-panel-i2c/main/ssd1306.cpp

@@ -1,6 +0,0 @@
-
-#include "ssd1306.h"
-
-// To use LV_COLOR_FORMAT_I1 we need an extra buffer to hold the converted data.
-// TODO: Remove this and SSD1306 can be header only.
-uint8_t SSD1306::oled_buffer_[LCD_H_RES * LCD_V_RES / 8];

esp/cpp/07_lcd-panel-i2c/main/ssd1306.h

@@ -25,8 +25,6 @@
 
 // According to SSD1306 datasheet.
 // https://cdn-shop.adafruit.com/datasheets/SSD1306.pdf
-#define LCD_H_RES              128
-#define LCD_V_RES              64
 #define I2C_HW_ADDR            0x3C
 #define LCD_PIXEL_CLOCK_HZ     (400 * 1000)
 // Bit number used to represent command and parameter
@@ -62,6 +60,9 @@ public:
       IPanelDevice(i2c,
                    (esp_lcd_panel_io_i2c_config_t) {
                        .dev_addr = I2C_HW_ADDR,
+                       // User data to pass to the LVGL flush_ready callback.
+                       // See IPanelDevice::lvgl_flush_ready_cb
+                       .user_ctx = nullptr,
                        .control_phase_bytes = 1,
                        .dc_bit_offset = 6,
                        .lcd_cmd_bits = LCD_CMD_BITS,
@@ -95,12 +96,6 @@ public:
   /// SSD1306 configuration structure.
   esp_lcd_panel_ssd1306_config_t ssd1306_config_;
 
-  /**
-   * Draw buffer for this panel device.
-   * For LV_COLOR_FORMAT_I1 we need an extra buffer to hold the converted data.
-   */
-  static uint8_t oled_buffer_[LCD_H_RES * LCD_V_RES / 8];
-
 private:
 
   //
@@ -113,12 +108,6 @@ private:
   {
     ESP_ERROR_CHECK(esp_lcd_new_panel_ssd1306(io, &config, &panel));
   }
-
-  //
-  // PRIVATE MEMBERS
-
-  /// Tag used for ESP logging.
-  const char * TAG = "SSD1306";
 };
 
 #endif // SSD1306_H

esp/cpp/07_lcd-panel-i2c/main/time_keeper.h

@@ -1,4 +1,3 @@
-
 #ifndef TIME_KEEPER_H
 #define TIME_KEEPER_H
 
@@ -20,13 +19,13 @@ struct Timer {
   explicit Timer(esp_timer_create_args_t args) :
       args_(args), esp_timer_(nullptr)
   {
-    ESP_LOGI(TAG, "Creating esp_timer with name: %s", args_.name);
+    ESP_LOGI(TAG, "Creating esp_timer with name: '%s'", args_.name);
     ESP_ERROR_CHECK(esp_timer_create(&args, &esp_timer_));
   }
 
   ~Timer()
   {
-    ESP_LOGI(TAG, "Destroying esp_timer with name: %s", args_.name);
+    ESP_LOGI(TAG, "Destroying esp_timer with name: '%s'", args_.name);
     ESP_ERROR_CHECK(esp_timer_delete(esp_timer_));
   }
 
@@ -51,7 +50,7 @@ private:
   // PRIVATE MEMBERS
 
   /// Tag used for ESP logging.
-  const char * TAG = "Timer";
+  constexpr static const char *TAG = "Timer";
 };
 
 /**
@@ -86,11 +85,11 @@ struct TimeKeeper {
    * @sa get_handle
    * @sa operator[](const char*)
    */
-  TimerHandle create_timer(esp_timer_create_args_t args)
+  [[maybe_unused]] TimerHandle create_timer(esp_timer_create_args_t args)
   {
     auto rt = managed_timers_.emplace(args.name, args);
     if (!rt.second) {
-      ESP_LOGE(TAG, "Display::Timer already exists with name %s", args.name);
+      ESP_LOGE(TAG, "Timer already exists with name '%s'", args.name);
       return nullptr;
     }
     return &rt.first->second;
@@ -105,7 +104,9 @@ struct TimeKeeper {
   /// Delete a Timer with the given name.
   [[maybe_unused]] void delete_timer(const char *name)
   {
-    managed_timers_.erase(name);
+    if (managed_timers_.erase(name) == 0) {
+      ESP_LOGE(TAG, "Attempt to delete timer that does not exist: '%s'", name);
+    }
   }
 
   /// Create a Timer with the ESP args and call esp_timer_start_periodic.
@@ -149,7 +150,7 @@ private:
   std::unordered_map<const char *, Timer> managed_timers_;
 
   /// Tag used for ESP logging.
-  const char * TAG = "TimeKeeper";
+  constexpr static const char *TAG = "TimeKeeper";
 };
 
 #endif // TIME_KEEPER_H

esp/cpp/07_lcd-panel-i2c/sdkconfig

@@ -2091,7 +2091,15 @@ CONFIG_MDNS_TASK_STACK_SIZE=4096
 CONFIG_MDNS_TASK_AFFINITY_CPU0=y
 # CONFIG_MDNS_TASK_AFFINITY_CPU1 is not set
 CONFIG_MDNS_TASK_AFFINITY=0x0
+
+#
+# MDNS Memory Configuration
+#
 CONFIG_MDNS_TASK_CREATE_FROM_INTERNAL=y
+CONFIG_MDNS_MEMORY_ALLOC_INTERNAL=y
+# CONFIG_MDNS_MEMORY_CUSTOM_IMPL is not set
+# end of MDNS Memory Configuration
+
 CONFIG_MDNS_SERVICE_ADD_TIMEOUT_MS=2000
 CONFIG_MDNS_TIMER_PERIOD_MS=100
 # CONFIG_MDNS_NETWORKING_SOCKET is not set