freertos_cheatsheet

FREERTOS Notes / Cheat Sheet

Heap

Heap_1 - Small embedded systems

• All memory allocation happens at start-up
• Pseudo "static"

Heap_2 - Deprecated

• Heap is allocated at task creation time
• available for backwards compatibility

Heap_3 - Standard malloc() free()

• thread-safe by temporarily suspending the scheduler

Heap_4 - First Fit Algorithm

• Coalescences adjacent free blocks together
• Single statically allocated array

Heap_5

• Identical to Heap_4 with the exception that heap_5 is not limited to allocating memory to a statically declared array
• Heap_5 can allocate memory from multiple and separate memory spaces

Task Management

• Tasks are concurrent functions
• Tasks must not be allowed to return, rather tasks infinitely loop
• Tasks have their own stack

Task Priorities

• configMAX_PRIORITIES should be kept to the minimum value necessary to minimize RAM usage
• set configUSE_PORT_OPTIMIISED_TASK_SELECTION to 1 if possible to take advantage of architecture specific optimizations
• The highest priority task will be selected to enter the running stage
• When more than one task is available at equal priority, each task will be scheduled round-robin

Time Measurement and Tick Interrupt

• configTICK_RATE_HZ sets the tick rate a typical value is 100
• pdMS_TO_TICKS( macro converts a time specific in milliseconds into a time specified in ticks (note that pdMS_TO_TICKS() cannot be used if configTICK_RATE_HZ is greater than 1000

Running State

Not Running State

BLocked State

• vTaskDelay() places the calling task into the Blocked state for a fixed number of tick interrupts

Suspended State

Ready State