HOWTO: Stop Serial buffer overflows

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HOWTO: Stop Serial buffer overflows

Posted by Jason on Wednesday November 07, @11:05AM
from the 1-more-solo-overflow dept.
I have 3 or 4 clients using ASUS motherboards with various version of FreeBSD from 3.4 to 4.4 using iDSL (isdn over frame relay). iDSL is a serial connection to the server. The problem I was experiencing is:

/kernel: sio0: 1 more silo overflow (total ##)

This would occur on a dial-up using a modem or iDSL. It didn't matter if the connect speed was set to 28800 or 115200. I didn't loose the connection, but wanted the error message to go away.

The Asus mobos have 16550A chips. After reading the man page for sio I started playing with the sio flags. The flag that corrected the problem disables FIFO.

I changed the serial device flag in my kernel config to the following:

device sio0 at isa? port IO_COM1 flags 0x00002 irq 4

Here are the flags listed in the man page for sio:

Meaning of flags:

0x00002 disable FIFO
0x00004 no AST/4 compatible IRQ control register
0x00008 recover sooner from lost output interrupts
0x00010 device is potential system console
0x00020 device is forced to become system
console 0x00040 device is reserved for low-level IO (e. g. for remote kernel debugging)
0x00080 use this port for remote kernel debugging
0x0??00 minor number of master port
0x20000 device is assumed to use a 16650A-type (extended FIFO) chip

If you would like to learn more about the sio device, read the man page:

man sio

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