Embedded RTOS and using malloc/free

Question

I am currently evaluating embOS from SEGGER running on Cortex M4F. It has 128 kilobytes of internal RAM, and 2 megabytes of external RAM, so I know I have plenty of memory.

My program uses some dynamic allocations (yes, I am aware that is not recommended on embedded systems).

When starting my task, I am trying to call malloc/OS_malloc, where the OS_malloc is the thread-safe version provided from embOS. In both cases, malloc failed and returned NULL pointer.

When doing the same malloc/OS_malloc before the OS starts, it works correctly:

**//Malloc here does not fail**
OS_IncDI();                      /* Initially disable interrupts  */
**//Malloc here does not fail**
OS_InitKern();                   /* Initialize OS                  */
**//Malloc here does  fail !!**
OS_InitHW();                     /* Initialize Hardware for OS    */

OS_CREATETASK(&TCBHP, "My Task", HPTask, 50, StackHP); //**<--And off course malloc failes inside teh task also**

OS_Start();

I went and tried using uCOS from MICRIUM, and I see the same behavior. Any ideas why this happens?

Answer 1

I think that i am on my way to fix the problem .

it seems that setting in the linker script :

_Min_Heap_Size = 0x19000; /* required amount of heap */ _Min_Stack_Size = 0x200; /* required amount of stack */

instead of :

_Min_Heap_Size = 0x00; /* required amount of heap */ _Min_Stack_Size = 0x200; /* required amount of stack */

Answer 2

malloc may returns fail in following condition

1)Running out of memory but as you said i have plenty of memory so this is not the case.

2)malloc is not able to allocate contiguous memory of requested size.

I guess option 2 is responsible for your case.