2nd serial port slow under Linux?

2nd serial port slow under Linux?

Post by Greg Broil » Sat, 16 Jul 1994 15:43:46


I've got what appears to be a generic 8-bit 2-port serial card; both
UARTs are 16550's. I/O over the first port (COM1:, or /dev/cua0)
works wonderfully - I/O over the second port (COM2:, or /dev/cua1)
is excruciatingly slow. This behavior occurs whether I'm trying to
log in at a prompt from agetty, or if I do a "cu -l /dev/cua1" and
send commands to the modem. Sending "ATZ" to the modem via /dev/cua0
gets me an "OK" immediately - sending "ATZ" to the same modem via
/dev/cua1 will get me an "OK" in 3-4 seconds. (The RD light on the
modem makes it appear that outbound characters go immediately.) As
you can imagine, the port isn't very useful to me in its current state.
I've tried swapping in a new 16550 and it didn't make a bit of
difference. I've also tried configuring the kernel for automatic
serial port configuration, or for manual configuration - and there
are no cards in the machine which conflict with the IRQ (IRQ 3).

I've looked through the docs and the source and the Serial-HOWTO,
but haven't seen anything that gives me any ideas. Has anyone else
experienced this? Is it a know bug? (Kernel is 1.0, from a Slackware
distribution with other bits tacked on. :)

Version: 2.5


"Over 2MB of news are posted each day. This is a staggering figure
when you consider that most news feeds are run over 1200 baud modems."
- Nemeth, et al, "Unix System Administration Handbook" (1989)


1. linux serial port nullcabled to pc - slow start

Dear linux crowd,

would you please help me out with serial port connections?
I am very much a newbie in linux and I can't take time to learn this thing
on my own, but if you direct me to the right how-to that will help too.

I have null modem cable connection from linux to a pc. when linux is
first loaded this connection is established (thru kermit) very fast.
however if it is terminated improperly during the session the next
connection takes 1-2 minutes to establish.

First it says: removing the LCK...modem.. file
then it sits there for a minute of two and then it connects.

just removing this file before the connection doesn't help at all. The
only thing that i found to help is to reboot linux.

I am sure there should be some simple solution for that. Please help
me out


 __    __      ____   ____
|  \  |  \    /    | /    \  Egor Alekseev
|  \  |  \   /  /| |/ /|  \  SSEL, University of Michigan
|  \__|  \  /  /\|   /\|  \  URL: http://www.umich.edu/~yegor

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