CMSIS - pros and cons

Hi,

We're entering a new project with STM32F7676 and thinking about which RTOS to use.

Our [initial] understanding is that CMSIS is a set of standardized APIs to peripherals, driver and to an actual RTOS implementation. Seems that the CMSIS solution is being strongly promoted (over using an RTOS w\o CMSIS).

As for the RTOS - seems we can pick from either CMSIS+RTX or CMSIS+FreeRTOS (?) or FreeRTOS w\o CMSIS.

Few basic questions on CMSIS itself:

- does CMSIS simply map APIs to the RTOS or does it actually add a layer of intermediate code?

- what overhead (e.g., code and size) does CMSIS add on top of the underlying RTOS?

- what additional dependencies are added when using CMSIS?

A couple of question on CMSIS + an RTOS:

- any pros and cons using CMSIS-RTX vs CMSIS+FreeRTOS?

- what are the pros and cons using CMSIS+FreeRTOS vs FreeRTOS w\o CMSIS?

Thanks!

--roy