From owner-freebsd-stable  Sat Mar  3 23:15:21 2001
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Date: Sat, 3 Mar 2001 23:14:25 -0800 (PST)
From: Rich Wales <richw@webcom.com>
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To: freebsd-stable@freebsd.org
Subject: Silo overflows
Message-ID: <20010304065203.30478.richw@wyattearp.stanford.edu>
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I'm running 4.2-RELEASE on an 800-MHz Athlon system.  One of the
serial ports on this machine is connected to the serial console port
on a second machine (my home firewall/bridge, running 4.2-STABLE).

The firewall's serial console speed is set to 115200.  The builtin
serial ports on both machines are 16550A's.

I'm getting lots and lots of silo overflows on the Athlon when I
generate a large amount of output from the firewall (e.g., if I do
"ls -ls", the output is badly garbled, and I get kernel messages on
the Athlon about silo overflows).

The Athlon's serial port (sio1) is using IRQ 3, and is =not= sharing
this IRQ with any other hardware on the system.

I've tried patching isa/sio.c to set a lower receive FIFO threshold,
but even with a threshold of FIFO_RX_MEDL, I still get silo overflows
unless I reduce the console speed to 19200 or slower.

I'm really surprised that I should be getting silo overflows on an
800-MHz Athlon -- which, I would think, should have plenty of computing
power available to handle serial interrupts without losing any input.

It works flawlessly, BTW, if I run Win98 on the Athlon and connect to
the firewall via Hyperterm -- so I assume the problem is in the FreeBSD
serial port driver, and not in my hardware.

I understand this "silo overflow" problem has been around for a long
time, but I wanted to bring it up again to make sure it wouldn't be
forgotten and would (hopefully) get fixed.

Rich Wales         richw@webcom.com         http://www.webcom.com/richw/


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