目录
- FreeRTOS学习第5篇--任务优先级
- 任务优先级
- 设计实验
- 任务一StartDefaultTask任务相关代码片段
- 任务二ColorLED_Test任务相关代码片段
- 任务三IRReceiver_Task相关代码片段
- 实验现象
- 本文中使用的测试工程
FreeRTOS学习第5篇–任务优先级
本文目标：学习与使用FreeRTOS中的任务优先级。
按照本文的描述，应该可以跑通实验并举一反三。
本文实验条件：拥有C语言基础，装有编译和集成的开发环境，比如：Keil uVision5
任务优先级
每个任务都有一个优先级，用来决定哪些任务可以被执行。在FreeRTOS中任务优先级数值越小，任务优先级越低。不过有时也记不住，直接看封装层的信息比较好，在文件cmsis_os2.h中定义了相关的优先级，看英文意思就是越往后优先级就越高的。
/// Priority values.
typedef enum {osPriorityNone = 0, ///< No priority (not initialized).osPriorityIdle = 1, ///< Reserved for Idle thread.osPriorityLow = 8, ///< Priority: lowosPriorityLow1 = 8+1, ///< Priority: low + 1osPriorityLow2 = 8+2, ///< Priority: low + 2osPriorityLow3 = 8+3, ///< Priority: low + 3osPriorityLow4 = 8+4, ///< Priority: low + 4osPriorityLow5 = 8+5, ///< Priority: low + 5osPriorityLow6 = 8+6, ///< Priority: low + 6osPriorityLow7 = 8+7, ///< Priority: low + 7osPriorityBelowNormal = 16, ///< Priority: below normalosPriorityBelowNormal1 = 16+1, ///< Priority: below normal + 1osPriorityBelowNormal2 = 16+2, ///< Priority: below normal + 2osPriorityBelowNormal3 = 16+3, ///< Priority: below normal + 3osPriorityBelowNormal4 = 16+4, ///< Priority: below normal + 4osPriorityBelowNormal5 = 16+5, ///< Priority: below normal + 5osPriorityBelowNormal6 = 16+6, ///< Priority: below normal + 6osPriorityBelowNormal7 = 16+7, ///< Priority: below normal + 7osPriorityNormal = 24, ///< Priority: normalosPriorityNormal1 = 24+1, ///< Priority: normal + 1osPriorityNormal2 = 24+2, ///< Priority: normal + 2osPriorityNormal3 = 24+3, ///< Priority: normal + 3osPriorityNormal4 = 24+4, ///< Priority: normal + 4osPriorityNormal5 = 24+5, ///< Priority: normal + 5osPriorityNormal6 = 24+6, ///< Priority: normal + 6osPriorityNormal7 = 24+7, ///< Priority: normal + 7osPriorityAboveNormal = 32, ///< Priority: above normalosPriorityAboveNormal1 = 32+1, ///< Priority: above normal + 1osPriorityAboveNormal2 = 32+2, ///< Priority: above normal + 2osPriorityAboveNormal3 = 32+3, ///< Priority: above normal + 3osPriorityAboveNormal4 = 32+4, ///< Priority: above normal + 4osPriorityAboveNormal5 = 32+5, ///< Priority: above normal + 5osPriorityAboveNormal6 = 32+6, ///< Priority: above normal + 6osPriorityAboveNormal7 = 32+7, ///< Priority: above normal + 7osPriorityHigh = 40, ///< Priority: highosPriorityHigh1 = 40+1, ///< Priority: high + 1osPriorityHigh2 = 40+2, ///< Priority: high + 2osPriorityHigh3 = 40+3, ///< Priority: high + 3osPriorityHigh4 = 40+4, ///< Priority: high + 4osPriorityHigh5 = 40+5, ///< Priority: high + 5osPriorityHigh6 = 40+6, ///< Priority: high + 6osPriorityHigh7 = 40+7, ///< Priority: high + 7osPriorityRealtime = 48, ///< Priority: realtimeosPriorityRealtime1 = 48+1, ///< Priority: realtime + 1osPriorityRealtime2 = 48+2, ///< Priority: realtime + 2osPriorityRealtime3 = 48+3, ///< Priority: realtime + 3osPriorityRealtime4 = 48+4, ///< Priority: realtime + 4osPriorityRealtime5 = 48+5, ///< Priority: realtime + 5osPriorityRealtime6 = 48+6, ///< Priority: realtime + 6osPriorityRealtime7 = 48+7, ///< Priority: realtime + 7osPriorityISR = 56, ///< Reserved for ISR deferred thread.osPriorityError = -1, ///< System cannot determine priority or illegal priority.osPriorityReserved = 0x7FFFFFFF ///< Prevents enum down-size compiler optimization.
} osPriority_t;
FreeRTOS 中任务的最高优先级是通过 FreeRTOSConfig.h 文件中的 configMAX_PRIORITIES 进行
配置的，用户实际可以使用的优先级范围是 0 到 configMAX_PRIORITIES – 1。这是我工程中优先级的宏定义，用户可以使用的优先级号是 0,1,2,3,4 …55，不包含 55
设计实验
基于以上信息的了解，我在我的硬件操作平台来设计一些实验来看一下相关的实验现象，创建3个优先级相同的任务，过一段时间后，我在我其中一个任务中设置一个更高的优先级，直接霸占cpu资源，让另两个任务没办法继续执行。基于这个设想，下面是相关代码片段。
任务一StartDefaultTask任务相关代码片段
osThreadId_t defaultTaskHandle;
const osThreadAttr_t defaultTask_attributes = {.name = "defaultTask",.stack_size = 128 * 4,.priority = (osPriority_t) osPriorityNormal,
};void StartDefaultTask(void *argument)
{/* USER CODE BEGIN StartDefaultTask *//* Infinite loop */for(;;){HAL_GPIO_TogglePin(LED1_GPIO_Port,LED1_Pin);HAL_GPIO_TogglePin(LED2_GPIO_Port,LED2_Pin);HAL_GPIO_TogglePin(LED3_GPIO_Port,LED3_Pin);mdelay(100);}/* USER CODE END StartDefaultTask */
}
/* creation of defaultTask */defaultTaskHandle = osThreadNew(StartDefaultTask, NULL, &defaultTask_attributes);
任务二ColorLED_Test任务相关代码片段
static StackType_t g_pucStackOfColorTask[75];
static StaticTask_t g_TCBofColorTask;
static TaskHandle_t xColorTaskHandle;
void ColorLED_Test(void * pvParameters)
{uint32_t color = 0;ColorLED_Init();while (1){//LCD_PrintString(0, 0, "Show Color: ");//LCD_PrintHex(0, 2, color, 1);ColorLED_Set(color);color += 200000;color &= 0x00ffffff;mdelay(1000);}
}
/* 创建任务: 色 */xColorTaskHandle = xTaskCreateStatic(ColorLED_Test, "ColorTask", 75, NULL, osPriorityNormal, g_pucStackOfColorTask, &g_TCBofColorTask);
任务三IRReceiver_Task相关代码片段
void IRReceiver_Task(void * pvParameters)
{uint8_t dev, data;OLED_Init();IRReceiver_Init();while(1){OLED_ShowString(0,0,"IR Receiver: ",16);OLED_ShowString(0,16,"Device Data",16);if (!IRReceiver_Read(&dev, &data)){OLED_ShowString(0, 32, " ",16);OLED_ShowNum(0,32,dev,4,16);OLED_ShowNum(64,32,data,4,16);OLED_ShowString(0, 48, " ",16);OLED_ShowString(0,48,"Key name: ",16);OLED_ShowString(80,48,(u8 *)IRReceiver_CodeToString(data),16);// 某个按键值if(data == 48){// 设置优先级vTaskPrioritySet(defaultTaskHandle, osPriorityAboveNormal2);}// 某个按键 if(data == 24){// 设置优先级vTaskPrioritySet(xColorTaskHandle, osPriorityAboveNormal1);}}OLED_Refresh(); // 刷新屏幕}}
xTaskCreate( IRReceiver_Task, "IRReceiver_Task", configMINIMAL_STACK_SIZE, NULL, osPriorityNormal, NULL );
其中要使用vTaskPrioritySet的函数，则需要在配置文件中配置相应的宏，默认是打开的。
实验现象
下载代码到板子上，一开始时，这三个任务的优先级都是osPriorityNormal级别的，都在按部就班的运行各自的功能函数，但是当我在IRReceiver_Task任务中按下相应的按键时，把对应的优先级任务提高之后，这三个任务中就只有一个高优先级的任务在执行了，直接霸占了cpu资源，让另两个任务都没法得到执行，连IRReceiver_Task后续也不执行了。为此本次实验设计成功。
本文中使用的测试工程
https://download.csdn.net/download/weixin_44317448/88666471
