An RTOS API defines the programming interface that the user interacts with when using the RTOS. Native APIs expose all of the RTOS's functionality. So far in this book, we've been using the native FreeRTOS API only. This was done to make it easier to search for help for a given function and to rule out any possibility of a poorly behaving wrapper layer between FreeRTOS and a generic API. However, this is not the only API option for FreeRTOS. There are also generic APIs available that can be used to interface with the RTOS functionality – but instead of being tied to a specific RTOS, they can be used across multiple operating systems.
These generic APIs are usually implemented as a wrapper layer above the native RTOS API (the exception to this is RTX, which has only the CMSIS-RTOS API). Here we can see where a typical API would...