Dynamic Memory Allocation
In the past, FreeRTOS commonly utilized the function
malloc()to allocate dynamic memory. As a result, if an application allowed
malloc()to allocate memory from external RAM (by configuring the CONFIG_SPIRAM_USE option as
CONFIG_SPIRAM_USE_MALLOC), FreeRTOS had the potential to allocate dynamic memory from external RAM, and the specific location was determined by the heap allocator.
Dynamic memory allocation for tasks (which are likely to consume the most memory) were an exception to the scenario above. FreeRTOS would use a separate memory allocation function to guarantee that dynamic memory allocate for a task was always placed in internal RAM.
Allowing FreeRTOS objects (such as queues and semaphores) to be placed in external RAM becomes an issue if those objects are accessed while the cache is disabled (such as during SPI flash write operations) and would lead to a cache access errors (see Fatal Errors for more details).
Therefore, FreeRTOS has been updated to always use internal memory (i.e., DRAM) for dynamic memory allocation. Calling FreeRTOS creation functions (e.g.,
xQueueCreate()) guarantees that the memory allocated for those tasks/objects is from internal memory (see FreeRTOS Heap for more details).
If you previously relied on CONFIG_SPIRAM_USE to place FreeRTOS objects into external memory, this change will lead to increased usage of internal memory due the FreeRTOS objects now being allocated there.
To place a FreeRTOS task/object into external memory, it is now necessary to do so explicitly. The following methods can be employed:
Manually allocate external memory for those objects using
heap_caps_malloc(), then create the objects from the allocated memory using one of the
esp_pm_config_esp32xx_tis deprecated, use
esp32xx/pm.his deprecated, use