The Cortex-M RT port also offers a compatibility layer with the CMSIS RTOS specification. The CMSIS RTOS API is mapped almost 1 to 1 on the RT native API, there is close to no overhead caused by the layer.
The implemented CMSIS RTOS features are:
Most CMSIS data types are mapped directly on the equivalent RT types.
The ChibiOS/RT own API is a superset of the features specified by the CMSIS specification.
Unfortunately CMSIS does not specify many features typical of an RTOS, for example and not limited to:
The equivalent RT API is available to fill this kind of gaps. The RT API is available even when using the CMSIS RTOS compatibility layer, mixed use is permitted.
When an exact behavior is not specified by CMSIS RTOS the equivalent RT behavior is to be expected.