Garbage data on config console after reset

[kzyapkov]

To reproduce: connect PB5 to GND and connect the USB cable. Open a screen session to the first serial port, observe some garbage data, no banner:

  *ed
Error, unknown command, use "help" to get the list of available commands.
>
>Ee    eree

This is reliably reproducible in my setup. Hitting enter does bring up the command prompt and the console can be used normally, the problem is just the garbage data at the beginning. Reproduces with main and r2axz-re-enumerate-on-reset.

Works OK if PB5 is connected to GND after the board has booted up and enumerated on the USB bus.

[r2axz]

Turns out it is not a bluepill-serial-monster bug, but a feature of Linux terminal subsystem. More details here:
https://stackoverflow.com/questions/14866899/linux-cdc-acm-device-unexpected-characters-sent-to-device