diff --git a/components/button/include/iot_button.h b/components/button/include/iot_button.h
index 8c7f8f088..ec548c8d9 100644
--- a/components/button/include/iot_button.h
+++ b/components/button/include/iot_button.h
@@ -29,8 +29,14 @@ typedef void *button_handle_t;
  * @brief Button events
  *
  */
-typedef enum {
-    BUTTON_PRESS_DOWN = 0,
+#ifdef __cplusplus
+typedef enum button_event_e : int { //C++ Definition
+#else
+typedef enum button_event_e {  //C Definition
+#endif
+	BUTTON_PRESS_INVALID = -1, //to enforce signed int also in C.
+	BUTTON_PRESS_NORMAL = 0,
+    BUTTON_PRESS_DOWN,
     BUTTON_PRESS_UP,
     BUTTON_PRESS_REPEAT,
     BUTTON_PRESS_REPEAT_DONE,
@@ -110,6 +116,7 @@ esp_err_t iot_button_delete(button_handle_t btn_handle);
  * @return
  *      - ESP_OK on success
  *      - ESP_ERR_INVALID_ARG   Arguments is invalid.
+ *      - ESP_ERR_INVALID_STATE the Callback is already registered. No free Space for another Callback.
  */
 esp_err_t iot_button_register_cb(button_handle_t btn_handle, button_event_t event, button_cb_t cb, void *usr_data);
 
diff --git a/components/button/iot_button.c b/components/button/iot_button.c
index 0b4d4e3a0..69794b449 100644
--- a/components/button/iot_button.c
+++ b/components/button/iot_button.c
@@ -97,6 +97,7 @@ static void button_handler(button_dev_t *btn)
         if (btn->button_level == btn->active_level) {
             btn->event = (uint8_t)BUTTON_PRESS_DOWN;
             CALL_EVENT_CB(BUTTON_PRESS_DOWN);
+            CALL_EVENT_CB(BUTTON_PRESS_NORMAL);
             btn->ticks = 0;
             btn->repeat = 1;
             btn->state = 1;
@@ -109,6 +110,7 @@ static void button_handler(button_dev_t *btn)
         if (btn->button_level != btn->active_level) {
             btn->event = (uint8_t)BUTTON_PRESS_UP;
             CALL_EVENT_CB(BUTTON_PRESS_UP);
+            CALL_EVENT_CB(BUTTON_PRESS_NORMAL);
             btn->ticks = 0;
             btn->state = 2;
 
@@ -123,6 +125,7 @@ static void button_handler(button_dev_t *btn)
         if (btn->button_level == btn->active_level) {
             btn->event = (uint8_t)BUTTON_PRESS_DOWN;
             CALL_EVENT_CB(BUTTON_PRESS_DOWN);
+            CALL_EVENT_CB(BUTTON_PRESS_NORMAL);
             btn->repeat++;
             CALL_EVENT_CB(BUTTON_PRESS_REPEAT); // repeat hit
             btn->ticks = 0;
@@ -145,6 +148,7 @@ static void button_handler(button_dev_t *btn)
         if (btn->button_level != btn->active_level) {
             btn->event = (uint8_t)BUTTON_PRESS_UP;
             CALL_EVENT_CB(BUTTON_PRESS_UP);
+            CALL_EVENT_CB(BUTTON_PRESS_NORMAL);
             if (btn->ticks < SHORT_TICKS) {
                 btn->ticks = 0;
                 btn->state = 2; //repeat press
@@ -165,6 +169,7 @@ static void button_handler(button_dev_t *btn)
         } else { //releasd
             btn->event = (uint8_t)BUTTON_PRESS_UP;
             CALL_EVENT_CB(BUTTON_PRESS_UP);
+            CALL_EVENT_CB(BUTTON_PRESS_NORMAL);
             btn->state = 0; //reset
             btn->long_press_hold_cnt = 0;
         }
@@ -326,6 +331,7 @@ esp_err_t iot_button_register_cb(button_handle_t btn_handle, button_event_t even
     BTN_CHECK(NULL != btn_handle, "Pointer of handle is invalid", ESP_ERR_INVALID_ARG);
     BTN_CHECK(event < BUTTON_EVENT_MAX, "event is invalid", ESP_ERR_INVALID_ARG);
     button_dev_t *btn = (button_dev_t *) btn_handle;
+    BTN_CHECK(NULL == btn->cb[event], "Callback is already registered", ESP_ERR_INVALID_STATE);
     btn->cb[event] = cb;
     btn->usr_data[event] = usr_data;
     return ESP_OK;
diff --git a/examples/camera/camera_components/esp32-camera b/examples/camera/camera_components/esp32-camera
new file mode 160000
index 000000000..108a33014
--- /dev/null
+++ b/examples/camera/camera_components/esp32-camera
@@ -0,0 +1 @@
+Subproject commit 108a33014902d2cc1b4e4523f6b14818288cb45e