Standard serial/parallel ports for new PC

[D. Hugh Redelmeier]

| From: Kevin Cozens <kevin-4dS5u2o1hCn3fQ9qLvQP4Q at public.gmane.org>

| The boards I have found are a in the $60 to close to $100 but seem to share a
| single IRQ. Since they do that, I would question their compatibility with the
| ports found on older computers.

PCI boards are supposed to use PCI bus interrupt request lines (INTA, INTB,
INTC, INTD).  That is all they can do.  It is the duty of the host
system to map these IRQ request lines to interrupt numbers.

So: it doesn't seem possible for a PCI board to emulate the old-style
interrupts purely in hardware.  The host could have a kludge to do the
trick.  Perhaps the BIOS could manage the trick (but how would it know
that it should?).  I don't think that a BIOS extension on the PCI card
could do this.



Slightly related issue:

If you have a hard to debug kernel problem, you might want to use a
serial console: then panic and oops messages might not be lost (or
hidden under the X screen).  Too bad that serial ports are going (have
gone) out of style, especially on laptops.

What can replace serial ports for this purpose?

- USB serial ports?  No: the serial console apparently requires that
  the device work with a wired-in driver that works before the USB bus
  is initialized.

- PCI board with serial ports?  I don't know.  I would guess that the
  PCI bus might be fundamental enough that it is initialized soon
  enough for this purpose.  It won't work on a laptop.  Annoyingly
  expensive.  And PCI slots might be disappearing.

- Parallel ports?  Yes, if the old fashioned hardware type.  Those are
  going away too.

- I wonder if an I2c or a PS/2 port could be used.

- ethernet would seem to require way too much protocol stack.
  Besides, it is probably not spare.
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