freertos

Name: freertos
Author: mohitmishra786

353installs19forks

How to install freertos?

mohitmishra786/low-level-dev-skills/freertos

$npx -y skills add mohitmishra786/low-level-dev-skills --skill freertos

Installs into the current project.

Summary

FreeRTOS skill for embedded RTOS development. Use when creating tasks, managing priorities, using queues and mutexes, detecting stack overflows, configuring FreeRTOS via FreeRTOSConfig.h, or debugging FreeRTOS applications with OpenOCD and GDB. Activates on queries about FreeRTOS

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SKILL.md

1	# FreeRTOS
2
3	## Purpose
4
5	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.
6
7	## Triggers
8
9	- "How do I create a FreeRTOS task?"
10	- "How do I pass data between FreeRTOS tasks?"
11	- "My FreeRTOS task is crashing — how do I detect stack overflow?"
12	- "How do I use FreeRTOS mutexes?"
13	- "How do I debug FreeRTOS tasks with GDB?"
14	- "How do I configure FreeRTOSConfig.h?"
15
16	## Workflow
17
18	### 1. Task creation and priorities
19
20	```c
21	#include "FreeRTOS.h"
22	#include "task.h"
23
24	// Task function signature
25	void vMyTask(void *pvParameters) {
26	const char name = (const char )pvParameters;
27	for (;;) {
28	// Task body — must never return
29	printf("Task %s running\n", name);
30	vTaskDelay(pdMS_TO_TICKS(500)); // yield for 500ms
31	}
32	}
33
34	int main(void) {
35	// xTaskCreate(function, name, stack_depth_words, param, priority, handle)
36	TaskHandle_t xHandle = NULL;
37	xTaskCreate(vMyTask, "MyTask",
38	configMINIMAL_STACK_SIZE + 128, // words, not bytes!
39	(void *)"sensor",
40	tskIDLE_PRIORITY + 2, // higher = more urgent
41	&xHandle);
42
43	vTaskStartScheduler(); // never returns if heap is sufficient
44	for (;;); // should never reach here
45	}
46	```
47
48	Priority guidelines:
49	- `tskIDLE_PRIORITY` (0) — idle task, never block here
50	- ISR-deferred tasks — highest priority to service interrupts quickly
51	- Avoid priorities above `configMAX_PRIORITIES - 1`
52
53	### 2. Queues — inter-task data passing
54
55	```c
56	#include "queue.h"
57
58	typedef struct { uint32_t sensor_id; float value; } SensorReading_t;
59
60	QueueHandle_t xSensorQueue;
61
62	void vProducerTask(void *pvParam) {
63	SensorReading_t reading;
64	for (;;) {
65	reading.sensor_id = 1;
66	reading.value = read_adc();
67	// Send; block max 10ms if queue full
68	xQueueSend(xSensorQueue, &reading, pdMS_TO_TICKS(10));
69	vTaskDelay(pdMS_TO_TICKS(100));
70	}
71	}
72
73	void vConsumerTask(void *pvParam) {
74	SensorReading_t reading;
75	for (;;) {
76	// Block forever until item available
77	if (xQueueReceive(xSensorQueue, &reading, portMAX_DELAY) == pdTRUE) {
78	process(reading.value);
79	}
80	}
81	}
82
83	// Create before starting scheduler
84	xSensorQueue = xQueueCreate(10, sizeof(SensorReading_t));
85	```
86
87	From ISR: use `xQueueSendFromISR()` and pass `&xHigherPriorityTaskWoken`.
88
89	### 3. Semaphores and mutexes
90
91	```c
92	#include "semphr.h"
93
94	// Binary semaphore — signaling (ISR→task)
95	SemaphoreHandle_t xSem = xSemaphoreCreateBinary();
96
97	void UART_ISR(void) {
98	BaseType_t xWoken = pdFALSE;
99	xSemaphoreGiveFromISR(xSem, &xWoken);
100	portYIELD_FROM_ISR(xWoken);
101	}
102
103	void vUartTask(void *p) {
104	for (;;) {
105	xSemaphoreTake(xSem, portMAX_DELAY);
106	// process received data
107	}
108	}
109
110	// Mutex — mutual exclusion (NOT from ISR)
111	SemaphoreHandle_t xMutex = xSemaphoreCreateMutex();
112
113	void vCriticalSection(void) {
114	if (xSemaphoreTake(xMutex, pdMS_TO_TICKS(100)) == pdTRUE) {
115	// protected access
116	shared_resource++;
117	xSemaphoreGive(xMutex);
118	}
119	}
120
121	// Recursive mutex (same task can take multiple times)
122	SemaphoreHandle_t xRecursive = xSemaphoreCreateRecursiveMutex();
123	xSemaphoreTakeRecursive(xRecursive, portMAX_DELAY);
124	xSemaphoreGiveRecursive(xRecursive);
125	```
126
127	Use mutex (not binary semaphore) for shared resources to get priority inheritance.
128
129	### 4. Stack overflow detection
130
131	```c
132	// FreeRTOSConfig.h
133	#define configCHECK_FOR_STACK_OVERFLOW 2 // Method 2 (pattern + watermark)
134	#define configUSE_MALLOC_FAILED_HOOK 1
135
136	// Implement the hook (called when overflow detected)
137	void vApplicationStackOverflowHook(TaskHandle_t xTask, char *pcTaskName) {
138	// Log the offending task name, then halt
139	configASSERT(0); // triggers assertion failure
140	}
141
142	void vApplicationMallocFailedHook(void) {
143	configASSERT(0);
144	}
145	```
146
147	Check watermarks at runtime:
148
149	```c
150	// Returns minimum ever free stack words
151	UBaseType_t uxHighWaterMark = uxTaskGetStackHighWaterMark(xHandle);
152	printf("Stack headroom: %lu words\n", uxHighWaterMark);
153	// Rule of thumb: keep headroom > 20 words
154	```
155
156	### 5. Essential FreeRTOSConfig.h settings
157
158	```c
159	// FreeRTOSConfig.h — adapt to your MCU
160	#define configCPU_CLOCK_HZ (SystemCoreClock)
161	#define configTICK_RATE_HZ 1000 // 1ms tick
162	#define configMAX_PRIORITIES 8
163	#define configMINIMAL_STACK_SIZE 128 // words
164	#define configTOTAL

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Type

freertos

353installs19forks

View on GitHub

How to install freertos?

mohitmishra786/low-level-dev-skills/freertos

$npx -y skills add mohitmishra786/low-level-dev-skills --skill freertos

Installs into the current project.

Summary

Files · 1

View on GitHub

SKILL.md

1	# FreeRTOS
2
3	## Purpose
4
5	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.
6
7	## Triggers
8
9	- "How do I create a FreeRTOS task?"
10	- "How do I pass data between FreeRTOS tasks?"
11	- "My FreeRTOS task is crashing — how do I detect stack overflow?"
12	- "How do I use FreeRTOS mutexes?"
13	- "How do I debug FreeRTOS tasks with GDB?"
14	- "How do I configure FreeRTOSConfig.h?"
15
16	## Workflow
17
18	### 1. Task creation and priorities
19
20	```c
21	#include "FreeRTOS.h"
22	#include "task.h"
23
24	// Task function signature
25	void vMyTask(void *pvParameters) {
26	const char name = (const char )pvParameters;
27	for (;;) {
28	// Task body — must never return
29	printf("Task %s running\n", name);
30	vTaskDelay(pdMS_TO_TICKS(500)); // yield for 500ms
31	}
32	}
33
34	int main(void) {
35	// xTaskCreate(function, name, stack_depth_words, param, priority, handle)
36	TaskHandle_t xHandle = NULL;
37	xTaskCreate(vMyTask, "MyTask",
38	configMINIMAL_STACK_SIZE + 128, // words, not bytes!
39	(void *)"sensor",
40	tskIDLE_PRIORITY + 2, // higher = more urgent
41	&xHandle);
42
43	vTaskStartScheduler(); // never returns if heap is sufficient
44	for (;;); // should never reach here
45	}
46	```
47
48	Priority guidelines:
49	- `tskIDLE_PRIORITY` (0) — idle task, never block here
50	- ISR-deferred tasks — highest priority to service interrupts quickly
51	- Avoid priorities above `configMAX_PRIORITIES - 1`
52
53	### 2. Queues — inter-task data passing
54
55	```c
56	#include "queue.h"
57
58	typedef struct { uint32_t sensor_id; float value; } SensorReading_t;
59
60	QueueHandle_t xSensorQueue;
61
62	void vProducerTask(void *pvParam) {
63	SensorReading_t reading;
64	for (;;) {
65	reading.sensor_id = 1;
66	reading.value = read_adc();
67	// Send; block max 10ms if queue full
68	xQueueSend(xSensorQueue, &reading, pdMS_TO_TICKS(10));
69	vTaskDelay(pdMS_TO_TICKS(100));
70	}
71	}
72
73	void vConsumerTask(void *pvParam) {
74	SensorReading_t reading;
75	for (;;) {
76	// Block forever until item available
77	if (xQueueReceive(xSensorQueue, &reading, portMAX_DELAY) == pdTRUE) {
78	process(reading.value);
79	}
80	}
81	}
82
83	// Create before starting scheduler
84	xSensorQueue = xQueueCreate(10, sizeof(SensorReading_t));
85	```
86
87	From ISR: use `xQueueSendFromISR()` and pass `&xHigherPriorityTaskWoken`.
88
89	### 3. Semaphores and mutexes
90
91	```c
92	#include "semphr.h"
93
94	// Binary semaphore — signaling (ISR→task)
95	SemaphoreHandle_t xSem = xSemaphoreCreateBinary();
96
97	void UART_ISR(void) {
98	BaseType_t xWoken = pdFALSE;
99	xSemaphoreGiveFromISR(xSem, &xWoken);
100	portYIELD_FROM_ISR(xWoken);
101	}
102
103	void vUartTask(void *p) {
104	for (;;) {
105	xSemaphoreTake(xSem, portMAX_DELAY);
106	// process received data
107	}
108	}
109
110	// Mutex — mutual exclusion (NOT from ISR)
111	SemaphoreHandle_t xMutex = xSemaphoreCreateMutex();
112
113	void vCriticalSection(void) {
114	if (xSemaphoreTake(xMutex, pdMS_TO_TICKS(100)) == pdTRUE) {
115	// protected access
116	shared_resource++;
117	xSemaphoreGive(xMutex);
118	}
119	}
120
121	// Recursive mutex (same task can take multiple times)
122	SemaphoreHandle_t xRecursive = xSemaphoreCreateRecursiveMutex();
123	xSemaphoreTakeRecursive(xRecursive, portMAX_DELAY);
124	xSemaphoreGiveRecursive(xRecursive);
125	```
126
127	Use mutex (not binary semaphore) for shared resources to get priority inheritance.
128
129	### 4. Stack overflow detection
130
131	```c
132	// FreeRTOSConfig.h
133	#define configCHECK_FOR_STACK_OVERFLOW 2 // Method 2 (pattern + watermark)
134	#define configUSE_MALLOC_FAILED_HOOK 1
135
136	// Implement the hook (called when overflow detected)
137	void vApplicationStackOverflowHook(TaskHandle_t xTask, char *pcTaskName) {
138	// Log the offending task name, then halt
139	configASSERT(0); // triggers assertion failure
140	}
141
142	void vApplicationMallocFailedHook(void) {
143	configASSERT(0);
144	}
145	```
146
147	Check watermarks at runtime:
148
149	```c
150	// Returns minimum ever free stack words
151	UBaseType_t uxHighWaterMark = uxTaskGetStackHighWaterMark(xHandle);
152	printf("Stack headroom: %lu words\n", uxHighWaterMark);
153	// Rule of thumb: keep headroom > 20 words
154	```
155
156	### 5. Essential FreeRTOSConfig.h settings
157
158	```c
159	// FreeRTOSConfig.h — adapt to your MCU
160	#define configCPU_CLOCK_HZ (SystemCoreClock)
161	#define configTICK_RATE_HZ 1000 // 1ms tick
162	#define configMAX_PRIORITIES 8
163	#define configMINIMAL_STACK_SIZE 128 // words
164	#define configTOTAL

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