serial console output - characters printed twice

[mcb30]

(2015-09-10 11:11)lupowolfi Wrote:  You were right, that was the "problem". Thank you for your fast help!

I did not realize that the PCBIOS console was enabled, because the option was commented out in config/console.h.
Undefining CONSOLE_PCBIOS in config/console.h solved my problem.

Sorry, I didn't explain myself clearly enough.

CONSOLE_PCBIOS is the "normal" console which writes to the screen and reads from the keyboard.

CONSOLE_SERIAL is iPXE's own serial port driver.

BIOS serial redirection is a feature implemented by your BIOS (and configurable via your BIOS setup screen) in which characters written to the screen will also be sent to the serial port.

The problem is that you have both CONSOLE_SERIAL and BIOS serial redirection enabled. iPXE writes each character both to the screen (due to CONSOLE_PCBIOS) and to the serial port (due to CONSOLE_SERIAL). Your BIOS then writes an additional copy of the character to the serial port, since you have BIOS serial redirection enabled. You therefore end up with two copies of each character on the serial port: one written directly by iPXE, one written by your BIOS.

The solution is to either disable CONSOLE_SERIAL or to disable your BIOS serial redirection (via your BIOS setup screen). Do not disable CONSOLE_BIOS unless you really don't want to be able to interact via a local keyboard and monitor.

You may find that iPXE's CONSOLE_SERIAL is more robust than your BIOS's serial redirection feature, and so it might be preferable to leave CONSOLE_SERIAL enabled and disable the BIOS serial redirection (via your BIOS setup screen).

Michael