This post contains personal learning notes regarding FreeRTOS and important contents extracted from the FreeRTOS Kernel Book .

Chapter 2

Ports

• Each supported combination of compiler and processor is called a FreeRTOS port.
• FreeRTOS is supplied as a set of C source files. Some source files are common to all ports, while others are specific to a port. Building the source files as part of your project makes the FreeRTOS API available to your application.

Data Types

TickType_t

• FreeRTOS configures a periodic interrupt called the tick interrupt.
• The number of tick interrupts that have occurred since the FreeRTOS application started is called the tick count. The tick count is used as a measure of time.
• TickType_t is the data type used to hold the tick count value, and to specify times. Its type depends on configTICK_TYPE_WIDTH_IN_BITS in FreeRTOSConfig.h.

BaseType_t

• BaseType_t is the data type used to define the most efficient data type for the architecture.
  • 64-bit type on a 64-bit architecture
  • 32-bit type on a 32-bit architecture
  • X-bit type on a X-bit architecture
• Generally used for return types that take only a very limited range of values, and for pdTRUE / pdFALSE type Booleans.

Variable Names

• Variables are prefixed with their type
  • a variable of type uint8_t will be prefixed with uc
  • a variable of type char* will be prefixed with pc

Function Names

• Functions are prefixed with both the type they return and the file they are defined within
  • vTaskPrioritySet() returns a void and is defined within tasks.c
  • xQueueReceive() returns a variable of type BaseType_t and is defined within queue.c
  • pvTimerGetTimerID() returns a void* and is defined within timers.c.
• File scope (private) functions are prefixed with prv.

Marco Names

• Most macros are written in upper case, and prefixed with lower case letters that indicate where the macro is defined
• Semaphore API is written almost entirely as a set of macros, but follows the function naming convention, rather than the macro naming convention.