FreeRTOS allocation error

Question

I am using FreeRTOS V6.1.1 on a STM32F107VC and get frequent malloc errors. The heap area is defined in the linker script but it keeps getting stuck in this loop of pvPortMalloc() after a few allocations:

while( ( pxBlock->xBlockSize < xWantedSize ) && ( pxBlock->pxNextFreeBlock != NULL ) )
{
    pxPreviousBlock = pxBlock;
    pxBlock = pxBlock->pxNextFreeBlock;
}

pxBlock: 0x20002300
pxPreviousBlock: 0x20002300
pxNewBlockLink: 0x00
xHeapHasBeenInitialised: 0x01

linker script:

/* Entry Point */
ENTRY(Reset_Handler)

/* Highest address of the user mode stack */
_estack = 0x20010000;    /* end of 64K RAM */

/* Generate a link error if heap and stack don't fit into RAM */
_Min_Heap_Size = 0;      /* required amount of heap  */
_Min_Stack_Size = 0x200; /* required amount of stack */

/* Specify the memory areas */
MEMORY
{
  FLASH (rx)      : ORIGIN = 0x08000000, LENGTH = 256K
  RAM (xrw)       : ORIGIN = 0x20000000, LENGTH = 64K
  MEMORY_B1 (rx)  : ORIGIN = 0x60000000, LENGTH = 0K
}

...

How can this be?

Answer 1

This was probably caused by fragmentation in heap_2.c. Even though the allocations were pretty small, the behaviour was consistent. Using heap_4.c solved it.