What is the maximum baud rate for USB CDC device on STM32L4 Discovery board? I am trying to send data from PC to MCU over loopback and I am receiving garbage data over the serial bus. Is this because of the baud rate?

[Bob S]

By "serial bus", do you mean USB? When means your data flow is PC -> USB -> STM32L4 -> USB -> PC ??? If so, baud rate should make no difference. The data is transferred as fast as the PC sends it, or as fast as the STM32L4 sends it back (at USB transfer speeds). Baud rate only matters if the STM32L4 is taking the data and sending it out over a real physical UART.

If this is strictly transfers over USB, does the data reach the MCU OK? You may need to instrument your MCU code to see this.