From ec3764886a7f203a6ef994a5da42a1f9ddfcf25b Mon Sep 17 00:00:00 2001
From: youhy <haoyuan2019@outlook.com>
Date: Tue, 19 Dec 2023 15:04:15 -0800
Subject: [PATCH 1/2] add eventflag example

---
 examples/rtos/CMakeLists.txt |  3 ++
 examples/rtos/eventflag.cc   | 95 ++++++++++++++++++++++++++++++++++++
 2 files changed, 98 insertions(+)
 create mode 100644 examples/rtos/eventflag.cc

diff --git a/examples/rtos/CMakeLists.txt b/examples/rtos/CMakeLists.txt
index e16531ab..4b93e664 100644
--- a/examples/rtos/CMakeLists.txt
+++ b/examples/rtos/CMakeLists.txt
@@ -28,3 +28,6 @@ irm_add_arm_executable(${PROJECT_NAME}_spin
     TARGET DJI_Board_TypeA
     SOURCES spinlock.cc)
 
+irm_add_arm_executable(${PROJECT_NAME}_eventflag
+    TARGET DJI_Board_TypeA
+    SOURCES eventflag.cc)
diff --git a/examples/rtos/eventflag.cc b/examples/rtos/eventflag.cc
new file mode 100644
index 00000000..e95bd918
--- /dev/null
+++ b/examples/rtos/eventflag.cc
@@ -0,0 +1,95 @@
+/****************************************************************************
+ *                                                                          *
+ *  Copyright (C) 2023 RoboMaster.                                          *
+ *  Illini RoboMaster @ University of Illinois at Urbana-Champaign          *
+ *                                                                          *
+ *  This program is free software: you can redistribute it and/or modify    *
+ *  it under the terms of the GNU General Public License as published by    *
+ *  the Free Software Foundation, either version 3 of the License, or       *
+ *  (at your option) any later version.                                     *
+ *                                                                          *
+ *  This program is distributed in the hope that it will be useful,         *
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of          *
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the           *
+ *  GNU General Public License for more details.                            *
+ *                                                                          *
+ *  You should have received a copy of the GNU General Public License       *
+ *  along with this program. If not, see <http://www.gnu.org/licenses/>.    *
+ *                                                                          *
+ ****************************************************************************/
+
+#include "bsp_gpio.h"
+#include "cmsis_os.h"
+#include "main.h"
+#include "utils.h"
+
+#define KEY_GPIO_GROUP GPIOB
+#define KEY_GPIO_PIN GPIO_PIN_2
+
+#define VX_READY_SIGNAL (1 << 1)
+
+/* Event flag example
+ * Press user key on type A board and the green led should toggle.
+ *
+ * The difference between event flag VS thread flag is:
+ * Event flag: thread -> event flag -> N threads
+ * Thread flag: thread -> specific thread
+ */
+
+static bsp::GPIO *gpio_green;
+BoolEdgeDetector key_detector(false);
+
+osEventFlagsId_t key_event_flag;
+
+static osThreadId_t LED_GREEN_TaskHandle;
+
+const osThreadAttr_t LED2Task_attributes = {.name = "LEDGreenTask",
+                                            .attr_bits = osThreadDetached,
+                                            .cb_mem = nullptr,
+                                            .cb_size = 0,
+                                            .stack_mem = nullptr,
+                                            .stack_size = 128 * 4,
+                                            .priority = (osPriority_t)osPriorityNormal,
+                                            .tz_module = 0,
+                                            .reserved = 0};
+
+void LED_GREEN_Task(void* argument) {
+  UNUSED(argument);
+  uint32_t flags;
+  while (true) {
+
+    flags = osEventFlagsWait(key_event_flag, VX_READY_SIGNAL, osFlagsWaitAny, osWaitForever);
+
+    if (flags & VX_READY_SIGNAL) {
+      print("\r\nOK!\r\n");
+      gpio_green->Toggle();
+      osDelay(200);
+    }
+  }
+}
+
+void RM_RTOS_Threads_Init(void) {
+  LED_GREEN_TaskHandle = osThreadNew(LED_GREEN_Task, nullptr, &LED2Task_attributes);
+}
+
+void RM_RTOS_Init(void) {
+  print_use_uart(&huart8);
+  gpio_green = new bsp::GPIO(LED_GREEN_GPIO_Port, LED_GREEN_Pin);
+  gpio_green->Low();
+
+  key_event_flag = osEventFlagsNew(nullptr);
+}
+
+void RM_RTOS_Default_Task(const void* args) {
+  UNUSED(args);
+  bsp::GPIO key(KEY_GPIO_GROUP, KEY_GPIO_PIN);
+  while (true) {
+    key_detector.input(key.Read());
+    if (key_detector.posEdge()) {
+
+      osEventFlagsSet(key_event_flag, VX_READY_SIGNAL);
+
+      print("event flag sent!");
+    }
+  }
+}

From 8cad513cb5d2884545988a401b83f53600535d1e Mon Sep 17 00:00:00 2001
From: youhy <haoyuan2019@outlook.com>
Date: Tue, 19 Dec 2023 15:30:04 -0800
Subject: [PATCH 2/2] add comments on error code

---
 examples/rtos/eventflag.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/examples/rtos/eventflag.cc b/examples/rtos/eventflag.cc
index e95bd918..34d9a223 100644
--- a/examples/rtos/eventflag.cc
+++ b/examples/rtos/eventflag.cc
@@ -59,7 +59,8 @@ void LED_GREEN_Task(void* argument) {
   while (true) {
 
     flags = osEventFlagsWait(key_event_flag, VX_READY_SIGNAL, osFlagsWaitAny, osWaitForever);
-
+    // Note that if osEventFlagsWait returns a error code (most commonly, timeout), flags is negative
+    // and only checking flags & SIGNAL is not enough
     if (flags & VX_READY_SIGNAL) {
       print("\r\nOK!\r\n");
       gpio_green->Toggle();