From owner-freebsd-bugs  Sat May  2 10:20:56 1998
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Date: Sun, 3 May 1998 03:16:56 +1000
From: Bruce Evans <bde@zeta.org.au>
Message-Id: <199805021716.DAA15845@godzilla.zeta.org.au>
To: dillon@backplane.com, freebsd-bugs@FreeBSD.ORG
Subject: Re: i386/5398
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> :actually, this is probably due to a device that isn't with-in the spec'd
> :rs-232 speeds...  I have the same problem with the ricochet on my
> :notebook... I can't run faster than 19.2kbps because the ricochet runs
> :about 5% over the 19.2kbps clock (I get about 2050int/sec at 19.2kbps)..
> :
> :try running the speeds lower...
> 
>     Ahh.... nonsense.  Unless the serial port is out of sync more then 1/2 
>     bit time every 10 bits, the 16x oversampling done by the 16xxx has no
>     problem dealing with this issue.  Also since the problem is demonstratably

It would need to be out of sync by -1/2 bit time every single bit for input
to appear to arrive much faster (about twice as fast).

>     cpu out of suds?  This is a pentium pro 200.  More likely, there is a 
>     serious interrupt disablement latency somewhere in the kernel.

More likely, there something outside the kernel is disabling interrupts.
Even more likely, the graphics card is using a significant fraction of
the bus bandwidth, so ISA interrupt handlers run much slower than normal.
It takes about a 10x slowdown to cause silo overflows with the default
fifo trigger level (4 times more when you reduce the level to 8).

Bruce

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