使用方法
- 复制安装命令，在自己的智能体环境安装前先检查源码包。
- 从原始文档核对所需工具、凭据和支持的宿主。
- 说明输入材料与期望交付物，并对照来源检查输出。
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill freertos开始前需了解
- 安装不包含模型订阅、API 额度或访问文件的权限。
- 仓库星数和安装量反映活跃情况，不等于独立质量或安全测试。
仓库原始内容
按源仓库内容呈现，保留标题、案例、代码、表格、链接以及原文引用的演示图片。
FreeRTOS
Purpose
Guide agents through FreeRTOS application development: task creation and priorities, inter-task communication with queues and semaphores, stack overflow detection, configASSERT, and FreeRTOS-aware debugging with GDB and OpenOCD.
Triggers
- "How do I create a FreeRTOS task?"
- "How do I pass data between FreeRTOS tasks?"
- "My FreeRTOS task is crashing — how do I detect stack overflow?"
- "How do I use FreeRTOS mutexes?"
- "How do I debug FreeRTOS tasks with GDB?"
- "How do I configure FreeRTOSConfig.h?"
Workflow
1. Task creation and priorities
c
#include "FreeRTOS.h"
#include "task.h"
// Task function signature
void vMyTask(void *pvParameters) {
const char *name = (const char *)pvParameters;
for (;;) {
// Task body — must never return
printf("Task %s running\n", name);
vTaskDelay(pdMS_TO_TICKS(500)); // yield for 500ms
}
}
int main(void) {
// xTaskCreate(function, name, stack_depth_words, param, priority, handle)
TaskHandle_t xHandle = NULL;
xTaskCreate(vMyTask, "MyTask",
configMINIMAL_STACK_SIZE + 128, // words, not bytes!
(void *)"sensor",
tskIDLE_PRIORITY + 2, // higher = more urgent
&xHandle);
vTaskStartScheduler(); // never returns if heap is sufficient
for (;;); // should never reach here
}Priority guidelines:
tskIDLE_PRIORITY(0) — idle task, never block here- ISR-deferred tasks — highest priority to service interrupts quickly
- Avoid priorities above
configMAX_PRIORITIES - 1
2. Queues — inter-task data passing
c
#include "queue.h"
typedef struct { uint32_t sensor_id; float value; } SensorReading_t;
QueueHandle_t xSensorQueue;
void vProducerTask(void *pvParam) {
SensorReading_t reading;
for (;;) {
reading.sensor_id = 1;
reading.value = read_adc();
// Send; block max 10ms if queue full
xQueueSend(xSensorQueue, &reading, pdMS_TO_TICKS(10));
vTaskDelay(pdMS_TO_TICKS(100));
}
}
void vConsumerTask(void *pvParam) {
SensorReading_t reading;
for (;;) {
// Block forever until item available
if (xQueueReceive(xSensorQueue, &reading, portMAX_DELAY) == pdTRUE) {
process(reading.value);
}
}
}
// Create before starting scheduler
xSensorQueue = xQueueCreate(10, sizeof(SensorReading_t));From ISR: use xQueueSendFromISR() and pass &xHigherPriorityTaskWoken.
3. Semaphores and mutexes
c
#include "semphr.h"
// Binary semaphore — signaling (ISR→task)
SemaphoreHandle_t xSem = xSemaphoreCreateBinary();
void UART_ISR(void) {
BaseType_t xWoken = pdFALSE;
xSemaphoreGiveFromISR(xSem, &xWoken);
portYIELD_FROM_ISR(xWoken);
}
void vUartTask(void *p) {
for (;;) {
xSemaphoreTake(xSem, portMAX_DELAY);
// process received data
}
}
// Mutex — mutual exclusion (NOT from ISR)
SemaphoreHandle_t xMutex = xSemaphoreCreateMutex();
void vCriticalSection(void) {
if (xSemaphoreTake(xMutex, pdMS_TO_TICKS(100)) == pdTRUE) {
// protected access
shared_resource++;
xSemaphoreGive(xMutex);
}
}
// Recursive mutex (same task can take multiple times)
SemaphoreHandle_t xRecursive = xSemaphoreCreateRecursiveMutex();
xSemaphoreTakeRecursive(xRecursive, portMAX_DELAY);
xSemaphoreGiveRecursive(xRecursive);Use mutex (not binary semaphore) for shared resources to get priority inheritance.
4. Stack overflow detection
c
// FreeRTOSConfig.h
#define configCHECK_FOR_STACK_OVERFLOW 2 // Method 2 (pattern + watermark)
#define configUSE_MALLOC_FAILED_HOOK 1
// Implement the hook (called when overflow detected)
void vApplicationStackOverflowHook(TaskHandle_t xTask, char *pcTaskName) {
// Log the offending task name, then halt
configASSERT(0); // triggers assertion failure
}
void vApplicationMallocFailedHook(void) {
configASSERT(0);
}Check watermarks at runtime:
c
// Returns minimum ever free stack words
UBaseType_t uxHighWaterMark = uxTaskGetStackHighWaterMark(xHandle);
printf("Stack headroom: %lu words\n", uxHighWaterMark);
// Rule of thumb: keep headroom > 20 words5. Essential FreeRTOSConfig.h settings
c
// FreeRTOSConfig.h — adapt to your MCU
#define configCPU_CLOCK_HZ (SystemCoreClock)
#define configTICK_RATE_HZ 1000 // 1ms tick
#define configMAX_PRIORITIES 8
#define configMINIMAL_STACK_SIZE 128 // words
#define configTOTAL_HEAP_SIZE (16 * 1024) // bytes
#define configMAX_TASK_NAME_LEN 16
// Debug / safety
#define configUSE_TRACE_FACILITY 1
#define configUSE_STATS_FORMATTING_FUNCTIONS 1
#define configCHECK_FOR_STACK_OVERFLOW 2
#define configUSE_MALLOC_FAILED_HOOK 1
#define configASSERT(x) if((x)==0) { taskDISABLE_INTERRUPTS(); for(;;); }
// Features
#define configUSE_MUTEXES 1
#define configUSE_RECURSIVE_MUTEXES 1
#define configUSE_COUNTING_SEMAPHORES 1
#define configUSE_TIMERS 1
#define configTIMER_TASK_STACK_DEPTH (configMINIMAL_STACK_SIZE * 2)6. GDB debugging with OpenOCD
bash
# Connect GDB with FreeRTOS thread awareness
# OpenOCD provides FreeRTOS-aware RTOS plugin
# openocd.cfg addition
# source [find rtos/FreeRTOS.cfg] # auto-loads with most targets
# GDB session
(gdb) info threads # lists all FreeRTOS tasks
(gdb) thread 3 # switch to task 3
(gdb) bt # backtrace of that task's stack
(gdb) frame 2 # inspect specific frame
# Print task list from GDB (if trace facility enabled)
(gdb) call vTaskList(buf)
(gdb) printf "%s\n", buf7. FreeRTOS v11 API updates
FreeRTOS v11 (2024+) extends task notifications and stream buffers:
c
// Task notifications v2 — 32-bit values with action semantics
xTaskNotifyIndexed(xHandle, 0, ulValue, eSetValueWithOverwrite);
xTaskNotifyWaitIndexed(0, 0, ULONG_MAX, &ulNotified, portMAX_DELAY);
// Stream buffers — ISR-safe send with trigger level
xStreamBufferSend(xStream, data, len, 0);
xStreamBufferSetTriggerLevel(xStream, 1); // wake receiver on 1 byteCheck FreeRTOS.h tskKERNEL_VERSION_NUMBER at compile time for API availability.
8. ARM TrustZone integration
Secure/non-secure world split on Cortex-M33/M55:
c
#include "secure_context.h"
// Initialize secure context management (secure side or NSC veneer)
SecureContext_Init();
// Allocate secure context for task calling secure functions
xTaskCreateSecure(vSecureTask, "SecTask", STACK, NULL, priority, &xHandle);
// MPU defines NSC (Non-Secure Callable) regions for SG veneersRequires TrustZone-enabled MCU, secure firmware partition, and NSC linker section placement.
9. FreeRTOS+TCP basics
c
#include "FreeRTOS_IP.h"
#include "FreeRTOS_Sockets.h"
// After network stack init (FreeRTOS_IPInit)
Socket_t xSocket = FreeRTOS_socket(FREERTOS_AF_INET, FREERTOS_SOCK_STREAM,
FREERTOS_IPPROTO_TCP);
FreeRTOS_connect(xSocket, &xAddress, sizeof(xAddress));
FreeRTOS_send(xSocket, buffer, len, 0);Configure buffer counts and TCP/IP options in FreeRTOSIPConfig.h (e.g., ipconfigUSE_TCP, ipconfigNUM_NETWORK_BUFFER_DESCRIPTORS). Pairs with an Ethernet MAC driver and FreeRTOS+TCP buffer management.
10. MPU region configuration
c
// Restricted task with MPU regions (Cortex-M with MPU)
static const TaskParameters_t xRestrictedTaskParams = {
.pvTaskCode = vRestrictedTask,
.pcName = "Restricted",
.usStackDepth = configMINIMAL_STACK_SIZE,
.pvParameters = NULL,
.uxPriority = tskIDLE_PRIORITY + 1,
.puxStackBuffer = stackBuffer,
.xRegions = {
{ .pvBaseAddress = 0x20000000, .ulLength = 0x10000,
.ulParameters = tskMPU_REGION_READ_ONLY | tskMPU_REGION_EXECUTE_NEVER },
{ .pvBaseAddress = 0x00000000, .ulLength = 0, .ulParameters = 0 } // terminator
}
};
xTaskCreateRestricted(&xRestrictedTaskParams, &xHandle);Define separate RAM regions for read-only code/data, privileged peripherals, and task-private stacks.
For OpenOCD setup details, see skills/embedded/openocd-jtag. For FreeRTOSConfig.h reference, see references/freertos-config.md.
Related skills
- Use
skills/embedded/openocd-jtagfor GDB/OpenOCD remote debugging setup - Use
skills/embedded/linker-scriptsfor placing FreeRTOS heap in specific RAM regions - Use
skills/debuggers/gdbfor general GDB session management - Use
skills/embedded/zephyrfor an alternative RTOS with built-in device management
