Return to BSD News archive
Received: by minnie.vk1xwt.ampr.org with NNTP id AA1215 ; Tue, 23 Feb 93 14:30:34 EST Path: sserve!manuel.anu.edu.au!munnari.oz.au!hp9000.csc.cuhk.hk!saimiri.primate.wisc.edu!usenet.coe.montana.edu!rpi!uwm.edu!cs.utexas.edu!qt.cs.utexas.edu!yale.edu!newsserver.jvnc.net!darwin.sura.net!haven.umd.edu!umd5!fcawth From: fcawth@eng.umd.edu (Fred Cawthorne) Newsgroups: comp.unix.bsd Subject: Re: I need a /dev/com3 !!! Message-ID: <18467@umd5.umd.edu> Date: 12 Feb 93 18:04:00 GMT References: <1993Feb8.170954.25245@vlsi.polymtl.ca> Sender: news@umd5.umd.edu Organization: /etc/organization Lines: 38 In article <1993Feb8.170954.25245@vlsi.polymtl.ca> lancio@shockley (Robert Lanciault) writes: > > I just want to know if it is possible to have a third >serial communication port. And what it has to be done to have one. > You can hack up old serial cards and change the interrupts of the ports, or get a card that OR's the interrupts together and use the new com drivers that support multiple ports on the same interrupt. The problem is that the irq line on the pc bus is active high, so you can't use open collector drivers or anything like that to have 2 different cards support the same interrupt. (so just using the usual com3 on a regular serial card is not possible...) I guess you could do something with tristate drivers, but I am not aware that io card designers are currently doing this. If you don't mind having a couple of wires going from card to card in your computer, you can cut the trace that goes to the irq line, and wire it to an or gate, along with all of the other devices you want to share that interrupt. The output of the or gate just goes to the interrupt line, and there's no contention. The software must be intelligent enough to figure out what is causing the interrupt if you plan to have the devices active at the same time. The new com driver takes care of this for 386bsd. At one time, I had 6 com ports in my machine, and all of them were hacked 2 port serial cards with 16550's in the second port. You can also use irq 10 and above if you don't mind making a little board to plug into the 16 bit extension of the ISA slot. Actually, if you have a spare interrupt in your computer, you could just run the interrupt from your current com3 to the irq9|5 spot on the 8 bit slot. Of course, you must recompile the kernel with the appropriate configuration for the ports... Some newer serial cards have a jumper for this already on the card. Note;Disclamer;etc: This is a "hack" solution, and should not be attempted by those not familiar with this type of thing. I only post this because I did not know if this would work before I tried, and I would have done it sooner if I knew someone else had done it successfully.