MC60/M66: Flush UART buffer immediately

I want to write serial data to the UART of MC60/M66 and flush it immediately (Used for RS485 data sending)
But i found that it will go to a middle buffer and after using Ql_Sleep it will be written on the hardware UART(1/2/3)

Is there a way to flush UART buffer immediately to the hardware?
its very important for me because i want to have full control on inter character timing of data

Please provide module model information, firmware information and SDK version.thank you

Module: M66FA-04-STDN
SDK: SDK 2.4
Revision: M66FAR01A12BT

Can anyone help me?

Please contact the local FAE to upgrade the firmware to the firmware version corresponding to the SDK version and then test it. Thank you.