Xref: utzoo comp.unix.i386:250 comp.sys.ibm.pc:34021
Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!mailrus!wuarchive!decwrl!decvax!ima!esegue!johnl
From: johnl@esegue.uucp (John R. Levine)
Newsgroups: comp.unix.i386,comp.sys.ibm.pc
Subject: Re: Slow printing in 386/ix
Summary: the 8259 is strange
Message-ID: <1989Sep1.004003.6311@esegue.uucp>
Date: 1 Sep 89 00:40:03 GMT
References: <1989Aug10.191352.8363@esegue.uucp> <2589@cbnewsc.ATT.COM>
Reply-To: johnl@esegue.UUCP (John Levine)
Distribution: usa
Organization: Segue Software, Cambridge MA
Lines: 30

In article <2589@cbnewsc.ATT.COM> psfales@cbnewsc.ATT.COM (Peter Fales) writes:
>In article <1989Aug10.191352.8363@esegue.uucp>, johnl@esegue.uucp (John Levine) writes:
>> I am running 386/ix 2.0.2 on a 25MHz Intel clone, to which I have attached
>> an HP Deskjet printer with the usual parallel interface.  It works, but the
>> printer runs at a small fraction of the speed at which it runs when I'm
>> running DOS.
>I had an AT&T 6386 WGS with a Deskjet printer that worked fine under DOS,
>but ran terribly slowly (a few characters/second) when I started running 
>UNIX/386.  After much trial and error, the problem turned out that another
>card in the system, a network card that I hadn't even installed the driver
>for, was tied to the same interrupt as the parallel interface.  Once I
>pulled that card out the system, things started working fine.

Well, what do you know.  I have an ethernet card for which I haven't
installed the driver, the rest of the network being several hundred miles
away.  I moved it from interrupt 7 to interrupt 2, and now the printer works
fine.

I gather that there is some aspect of the 8259 interrupt controller chip so
that if an interrupt request comes and goes away, as happens with the
unlatched printer request line, the 8259 interrupts anyway on level 7.
(That was reputed to be the excuse for not latching the printer request so
they could avoid a 50 cent flip-flop on the card.)  Did the network card
make that fail, or is it more likely that having two devices on the same
interrupt line made the printer unable to request the interrupt in the first
place?  Perhaps someone with more 8259 combat experience would know.
-- 
John R. Levine, Segue Software, POB 349, Cambridge MA 02238, +1 617 492 3869
{ima|lotus}!esegue!johnl, johnl@ima.isc.com, Levine@YALE.something
Massachusetts has 64 licensed drivers who are over 100 years old.  -The Globe