Very Computer

Hello,
        I currently have two parallel ports in my PC (one at address 0x3bc and
one at 0x378) and was wondering if it is possible to use them simultaneously
_without_ using more than one interrupt.  I've read that in DOS, most printing
is not interrupt-driven, but instead is accomplished by polling.  Having read
the Printing-HOWTO, I have learned that it is possible (under Linux) to toggle
between an interrupt driver and a polling driver for each parallel port
(/dev/lp0, /dev/lp1) using a utility called "tunelp".  I was wondering if any
of the following configurations are possible for simultaneous use of the two
parallel ports:

1) Have both ports share IRQ7.

2) Have both ports run with the polling driver (using no interrupts).

3) Have one port using IRQ7 and the other port running with the polling driver.

I know that I can set the two parallel ports up using separate interrupts, but
the card with the second parallel port only allows use of IRQ7 or IRQ5 (it's
an 8-bit I/O card), and IRQ7 is already used by my first parallel port (it's
integrated onto the motherboard and its IRQ is not changeable) and IRQ5 is
being used by an old MIDI interface card (whose IRQ is also not changeable).  
Any comments/suggestions are greatly appreciated!

-Alvin

You can set up both ports to not use an IRQ at all; they should have
no problem at all running this way together, although the polling
driver is rather CPU-intensive.  I think polling is the default
behavior for printer ports anyway: I've never had any of mine set up
to use an IRQ and they work just fine.  One port on on IRQ7 and one on
no interrupt (polling) should work also; setting both to the same
interrupt almost certainly won't work without hardware mods...

BTW, disabling printer-port interrupts is usually as easy as pulling
one jumper; in extreme cases (old boards) you'll have to cut the IRQ 7
trace coming in.

Keep in mind that interrupts are needed if you want to use your ports
with PLIP (as communication links to another Linux box), rather than
just as printer ports.

-- alex