Hi Markus:
There is no special reason for no flexCAN freeRTOS driver. I will issue a new feature request to the develop team.
The FreeRTOS driver is a wrapper built on top of standard SDK peripheral drivers.
The wrappers provide an API which blocks the calling task until the I/O operation completes and allows other tasks to run. This is achieved by using the asynchronous API of the underlying driver along with RTOS task synchronization object.
You can refer to the FreeRTOS usart driver in SDK installation folder. I am assuming you are using K64.
SDK_2.5.0_TWR-K64F120M\devices\MK64F12\drivers\fsk_uart_freertos.c
SDK_2.5.0_TWR-K64F120M\devices\MK64F12\drivers\fsk_uart_freertos.h
Regards
Daniel