Re: Support for serial console on legacy free machines

From: Andreas Dilger (
Date: Mon Jul 30 2001 - 17:40:31 EST

Khalid Aziz writes:
> Andreas Dilger wrote:
> > Has anyone considered allowing console devices to run over bi-directional
> > parallel ports? I imagine most of the required code is in PLIP and serial,
> > which unfortunately I know nothing about.
> >
> > Several newer systems I have today do not have physical serial ports at all,
> > but all of them (even laptops) still have bi-directional parallel ports.
> >
> > I suppose there may be some difficulties in exporting a "serial-like"
> > interface to the user apps (e.g. minicom and such), but maybe not.
> >
> SH supports console on line printer which I assume is a parallel port
> console. You can check if that code will work for you and if it can be
> ported to x86.

 From what I have been told, the "line printer console" is unidirectional
only. This would make it OK for console output, but you could not do real
debugging over such a setup.

What bothers me is that new systems don't have a serial port, and no ISA
slots, so there is no hope of getting a "serial console" support without
ACPI (which is rather heavyweight AFAIK). USB is far too complex to use
for early-boot debugging, so what else is left?

There was some talk about using a low level IP console over ethernet,
but I would imagine this is more complex than the same thing on a
parallel-port. I could be wrong. Of course, an IP console has the
advantage of being useful over a longer distance than a parallel cable,
but may have the disadvantage of poor security.

Cheers, Andreas

Andreas Dilger  \ "If a man ate a pound of pasta and a pound of antipasto,
                 \  would they cancel out, leaving him still hungry?"               -- Dogbert

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