Virtual serial port questions to consult

freeRTOS use virtual serial port? If the support, can be switched threads between sending each bit of uart data? Where can I find this demo.
If freeRTOS don’t support virtual serial function,would you tell me reason.
thank you every one.

FreeRTOS can integrate with virtual serial ports, but does not provide an implementation itself. You will find FreeRTOS working with commercial USB drivers from companies like HCC Embedded, or with open source drivers from companies such as Atmel (now Microchip). I think there are some really old demos in the FreeRTOS download with open source USB.