Timeout broken with serial port

[Michal Suchanek]

Hello,

I was experiencing a mysterious error with grub. It would not boot
with timeout set.

It turns out that setting serial IO disables timeout.

grub-pc        1.99-11ubuntu1

I think it used to work with earlier grub, I have this file for ages:

# cat /etc/grub.d/03_serial
#!/bin/sh

echo serial --unit=0 --speed=115200
echo terminal_input --append serial\; terminal_output --append serial