feat(esp_timer): Move esp_timer-related init steps into the component

components/esp_timer/CMakeLists.txt

@@ -4,6 +4,7 @@ if(${target} STREQUAL "linux")
     idf_component_register(INCLUDE_DIRS include)
 else()
     set(srcs "src/esp_timer.c"
+             "src/esp_timer_init.c"
              "src/ets_timer_legacy.c"
              "src/system_time.c"
              "src/esp_timer_impl_common.c")
@@ -21,4 +22,7 @@ else()
     idf_component_register(SRCS "${srcs}"
                            INCLUDE_DIRS include
                            PRIV_INCLUDE_DIRS private_include)
+
+    # Forces the linker to include esp_timer_init.c
+    target_link_libraries(${COMPONENT_LIB} INTERFACE "-u esp_timer_init_include_func")
 endif()

components/esp_timer/src/esp_timer.c

@@ -514,15 +514,6 @@ static IRAM_ATTR inline bool is_initialized(void)
     return s_timer_task != NULL;
 }
 
-esp_err_t esp_timer_early_init(void)
-{
-    esp_timer_impl_early_init();
-#if CONFIG_ESP_TIME_FUNCS_USE_ESP_TIMER
-    esp_timer_impl_init_system_time();
-#endif
-    return ESP_OK;
-}
-
 static esp_err_t init_timer_task(void)
 {
     esp_err_t err = ESP_OK;
@@ -582,7 +573,14 @@ esp_err_t esp_timer_init(void)
 #define ESP_TIMER_INIT_MASK ESP_SYSTEM_INIT_ALL_CORES
 #endif // CONFIG_ESP_TIMER_ISR_AFFINITY_*
 
-ESP_SYSTEM_INIT_FN(esp_timer_startup_init, SECONDARY, ESP_TIMER_INIT_MASK, 100)
+/*
+ * This function initializes a task and ISR that esp_timer uses.
+ *
+ * We keep the esp_timer initialization function here to allow the linker
+ * to automatically include esp_timer_init_os if other components call esp_timer APIs.
+ * If no other code calls esp_timer APIs, then esp_timer_init_os will be skipped.
+*/
+ESP_SYSTEM_INIT_FN(esp_timer_init_os, SECONDARY, ESP_TIMER_INIT_MASK, 100)
 {
     return esp_timer_init();
 }

components/esp_timer/src/esp_timer_init.c

@@ -0,0 +1,35 @@
+/*
+ * SPDX-FileCopyrightText: 2024 Espressif Systems (Shanghai) CO LTD
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include "esp_private/startup_internal.h"
+#include "esp_timer_impl.h"
+#include "sdkconfig.h"
+
+esp_err_t esp_timer_early_init(void)
+{
+    esp_timer_impl_early_init();
+#if CONFIG_ESP_TIME_FUNCS_USE_ESP_TIMER
+    esp_timer_impl_init_system_time();
+#endif
+    return ESP_OK;
+}
+
+/*
+ * This function starts a timer, which is used by esp_timer
+ * to count time from the very start of the application.
+ *
+ * Another initialization function, esp_timer_init_nonos (which initializes ISR and task),
+ * is called only if other code calls the esp_timer API.
+ */
+ESP_SYSTEM_INIT_FN(esp_timer_init_nonos, CORE, BIT(0), 101)
+{
+    return esp_timer_early_init();
+}
+
+void esp_timer_init_include_func(void)
+{
+    // Hook to force the linker to include this file
+}