Interrupt sharing with 16552 serial ports?

Interrupt sharing with 16552 serial ports?

Post by Urs Thuerman » Thu, 22 May 1997 04:00:00

I have a multi I/O card which has 4 serial, 3 parallel, and 1 game
port.  For each of the serial and parallel ports there is a jumper to
set the IRQ to one of 3,4,5,7,9,10,11,12,15.  For each serial port
there is a additional jumper to the port address to one of {2,3}{e,f}8
while the parallel ports can be set to 278, 378 or 3bc.

The card has two 16552 and one 86c451 chip.

The Linux kernel recognizes 4 serial ports at the 4 different
addresses as set by the jumpers.

My questions is, wether this card is multiport card as described in
the Serial-HOWTO, i.e. which can share one IRQ among several serial

I have set the jumpers for ttyS0 and ttyS2 to IRQ 4, the other two to
IRQ 3.

When I start X, the mouse connected to ttyS0 works correctly.  But
when I then type

        cat /dev/ttyS2 >foo

the mouse movements aren't seen by the X server anymore.  It seems
when an IRQ 4 occurs the interrupt routine tries to read from ttyS2
only, as long as it is opened.  If I kill the cat, the mosue operates

The guy from which I bought this card has used it with the same jumper
setting, i.e. two serial ports per IRQ, but on an OS other than Linux.
I don't know I he has used two of those ports simulanously.

Can I use two serial ports on this card simulanously using the same



1. Serial Ports and Shared Interrupts?

It works with PCMCIA and PCI. It will _sometimes_ work with ISA.

You must modify the hardware! Add a resister and diode I think.
When one card issues an IRQ and the other doesn't, the stronger
card wins. Depending on the cards and motherboard, it could work.
Computers usually deal in on/off, not on/half-on/off.

Note that you could damage hardware.
Albert Cahalan
acahalan at (no junk mail please - I will hunt you down)

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