FreeRTOS memory management understanding

Kernel
1

sachingole wrote on Tuesday, June 27, 2017:

Hi All,

Configuration I am using as below :

define configMINIMAL_STACK_SIZE ((uint16_t)512)
define configTOTAL_HEAP_SIZE ((size_t)(75 * 1024))
define configLARGE_STACK_SIZE ((uint16_t)3072)

Heap memory = 75KB
3 threads created, thread 1 with 512 stack, thread 2 with 512 stack and thread 3 with 3KB

Following is function call sequence and respective memory allocation debug message :-

  1. FreeHeap = 0, StackHighWaterMark = 0, xTaskGetTickCount = 0
  2. xQueue = xQueueCreate( mainQUEUE_LENGTH, sizeof( unsigned long ) );
  3. FreeHeap = 76696, StackHighWaterMark = 0, xTaskGetTickCount = 0
  4. xReturned = xTaskCreate( prvQueueReceiveTask, “Rx”, configMINIMAL_STACK_SIZE, NULL, mainQUEUE_RECEIVE_TASK_PRIORITY, NULL );
  5. prvQueueReceiveTask created.
  6. FreeHeap = 74536, StackHighWaterMark = 501, xTaskGetTickCount = 0
  7. xReturned = xTaskCreate( prvQueueSendTask, “TX”, configMINIMAL_STACK_SIZE, NULL, mainQUEUE_SEND_TASK_PRIORITY, NULL );
  8. prvQueueSendTask created.

9.** FreeHeap = 72376, StackHighWaterMark = 501, xTaskGetTickCount = 0**
10. xReturned = xTaskCreate( prvRamDiskTask, “DISK”, (configLARGE_STACK_SIZE), NULL, tskIDLE_PRIORITY, &xHandle );
11. prvRamDiskTask created.
12. FreeHeap = 59976, StackHighWaterMark = 501, xTaskGetTickCount = 0
13. FreeHeap = 57816, StackHighWaterMark = 3033, xTaskGetTickCount = 9

Q. 2KB memory got allocated after each thread creation in case of first 2 threads, but suddenly 12KB memory got allocated after 3rd thread creation. Change is in case of 3rd thread is 3KB stack is configured.

Can any one help to understand why this much memory got allocated at each stage.

Best regards,
Sachin

2

rtel wrote on Wednesday, June 28, 2017:

As is documented in the API documentation, in the source code, and in
the book, the stack size parameter to xTaskCreate() is specified in
words. The numbers you have provided would indicate that you are using
a 32-bit processor. Each item on the stack is 32-bits, so when you
specify a stack size of 512 words 2K bytes get allocated. When you
specify a stack of 3K words, 12K bytes get allocated.

3

sachingole wrote on Wednesday, June 28, 2017:

Thank you for information.