From owner-freebsd-questions  Fri Aug 20 12:33:54 1999
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Date: Fri, 20 Aug 1999 12:33:13 -0700
From: Kent Stewart <kstewart@3-cities.com>
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To: Morten Seeberg <morten@seeberg.dk>
Cc: questions@FreeBSD.ORG
Subject: Re: 4 seriel ports
References: <001401beeb3e$21389a90$1600000a@SOS>
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Morten Seeberg wrote:
> 
> Hi, AFAIR it is possible on x86 systems (or atleast windows and dos :) ) to
> have 4 serial ports, which share 2 IRQs?? (I have 2 onboard serieal ports
> and an xtra I/O card.
> How is this done on BSD? And which restrictions would I have, in DOS i
> remember, that it wasnt a good idea to put a mouse and a modem on 2 serial
> ports, which share IRQ, maybe this problem is solved on newer computers.
> 
> So that:
> COM1    IRQ4
> COM2    IRQ3
> COM3    IRQ4
> COM4    IRQ3
> 
> This doesnt seem possible with the SIO driver (the man says so). But I hope
> that it is possible? And where should I look?
> 
> I tried it with the following parameters:
> options         "COM_MULTIPORT"
> device          sio0    at isa? port "IO_COM1" tty
> device          sio1    at isa? port "IO_COM2" tty
> device          sio2    at isa? port "IO_COM3" tty
> device          sio3    at isa? port "IO_COM4" tty
> 
> This is the result:
> DMESG:
> sio0 at 0x3f8-0x3ff on isa
> sio0: type 16550A
> sio1 at 0x2f8-0x2ff on isa
> sio1: type 16550A
> sio2 at 0x3e8-0x3ef on isa
> sio2: type 16450
> sio3 at 0x2e8-0x2ef on isa
> sio3: type 16450
> -----
> fw.home:/root#cu -l /dev/cuaa2
> Connected.
> atz
> Aug 20 18:21:29 fw /kernel: sio2: 1 more silo overflow (total 2)
> Aug 20 18:21:29 fw /kernel: sio2: 1 more silo overflow (total 2)

This could be because of how you are sharing interrupts. At some point
in my distant past, you could share interrupts but they had to be on
the same card. So the add on card would be com2 and com4, which could
share an interrupt and com1 and com3 on the PC. You will have problems
at some line speed above 9.6kb because you don't have a 16550A on your
addon ports, which can cause overflows because the 450 doesn't have
the FIFO.

Kent

> 
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /\/\orten $eeberg, Systems Consultant @
> Merkantildata CMA - Enterprise Solutions
> #echo 'System Administrators suck :)' > /dev/console
> 
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-- 
Kent Stewart
Richland, WA

mailto:kstewart@3-cities.com
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