Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!bloom-beacon!husc6!bbn!uwmcsd1!marque!uunet!mcvax!enea!kth!draken!chalmers!myab!herder
From: herder@myab.se (Jan Herder)
Newsgroups: comp.unix.microport
Subject: Re: Losing interrupts?
Message-ID: <445@myab.se>
Date: 4 Oct 88 15:59:30 GMT
References: <NELSON.88Sep29160014@sun.soe.clarkson.edu> <553@micropen> <1900@van-bc.UUCP>
Reply-To: herder@myab.UUCP (Jan Herder)
Organization: Myab Gothenburg, Sweden
Lines: 34

In article <1900@van-bc.UUCP> sl@van-bc.UUCP (pri=-10 Stuart Lynne) writes:
<However we take note that SCO mysteriously looses far less than Microport.
<The reason of course is that Microport spends a *lot* more time at spl7 than
<SCO does. This exacerbates the problem that you mention.  
<
<In my experience system interrupt overhead and time lost through use of spl7
<is the primary cause of lost interrupts. At least when they are lost due to
<a large influx of them.
<
<SCO apparently has spent much time and effort in finding all places where
<spl7 is needed and *not* needed and has reduced the amount of time when they
<lock them out. 
<
<For example with the tty drivers, try the following:
<
<	stty 19200 -ixoff -echo; cat > /tmp/test
<
<then from your terminal emulator program dump about 100kb of data to the
<system. 

There are ways to dealing with this problem, it's called pseudo dma.
If you have dumb serial port, you make a very small interrupt ruotine
wich reads the uart and puts the characters in a big circular list, which
can be read at a later time. If you make sure to never lock out this small
interrupt routine you don't loose any characters. 

This technic has been used whith DZ ports on VAXen and serial ports on SUNs.
The *RIGHT* way to do it is of course to get a better serial card.

-- 
Jan Herder, MYAB Sweden                    |  Phone: +46 31 18 75 12
Internet: herder@myab.se                   |  Fax:   +46 31 18 28 42
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