From owner-freebsd-stable  Fri Sep  1 11:53:45 2000
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To: "Jim King" <jim@jimking.net>
Subject: Re: bad 16550A maybe? 
Cc: "Gary Kline" <kline@thought.org>, freebsd-stable@FreeBSD.ORG
In-reply-to: Your message of "Fri, 01 Sep 2000 13:41:01 CDT."
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References: <002d01c01444$350c8b00$a44b8486@jking>  <200009010501.WAA54972@tao.thought.org> <200009011832.MAA37168@harmony.village.org> 
Date: Fri, 01 Sep 2000 12:53:12 -0600
From: Warner Losh <imp@village.org>
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In message <002d01c01444$350c8b00$a44b8486@jking> "Jim King" writes:
: I think we'd see a lot fewer of these messages on the mailing lists if sio.c
: set the 16550A trigger level to 8 bytes instead of 14 bytes.  That's the
: first thing I do when I see this problem, and that usually fixes it; much
: easier than replacing the misbehaving hardware. :-)

For fast machines, this is a lose since it double the interrupt rate,
but does give a *MUCH* better interrupt latency tolerance.  I had to
do this when i had a 16550A attached to a custom card via PCI.  I
couldn't make it have fast interrupts, so I did the next best thing by
increasing the number of interrupts and checking more often (the card
itself had about half a dozen interrupts going all the time, so long
as I could afford a 16ms latency I was fine).

Warner


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