Serial console (Re: Running headless)

Jaakko Hyvatti (Jaakko.Hyvatti@www.fi)
Fri, 21 Jul 1995 11:24:07 +0200 (EET DST)

Andreas Koppenhoefer <koppenas@koppenas.informatik.uni-stuttgart.de>:
> What we need is a kernel function which is capable of redirecting
> printk's text output to serial device. And this function must be
> registered with register_console(serial_print). Just implenent
> serial_print() and you're finished.

Uh, I believe many have done this to debug their systems, me amongst
them. After one has solved his problems, none has had any interest to
refine the patches so that they could be included in kernel releases.
If anyone wishes to experiment, my ancient patches can be found at

ftp://www.fi/pub/linux/diffs/kernel/old/linux-1.1.serial_console.diff

which seem to be against 1.1.81. They also add kernel command line
optios to define multiple serial consoles, and kernel messages appear
on all the defined serial consoles and on system console too:

console=0 console=2

means /dev/ttyS0 and ttyS2 get the messages.

The problem with serial console is that you cannot trust on interrupts
but have to poll the chip. That's bad and may affect the timings in
other drivers.