serial port initialization

serial port initialization

Post by Andries Kruith » Wed, 22 Feb 1995 22:21:22

Hi all,

I've got the following configuration:

Pentium 60MHz, 2 serial ports: 1x16450, 1x16550
Printer NEC P6 connected to serial port #2 (/dev/ttyS1)
Linux kernel V1.1.89

I'm trying to set up the serial port to correctly talk to the printer.
Under DOS this works fine, by specifing 'MODE COM2: 9600,n,8,1,B'
(the B is for retrying to send characters to the printer when the
device is not ready yet)

Under Linux I've tried several settings for the serial port, but
without succes. I can send files to the printer, but when the printer
signals that its buffer is full, this is not recognized by linux.
This means that I can send any file smaller then 2 KByte to the printer,
and it will print correctly, but files larger then 2 KByte are not
printed completely (the printer has an internal 2 KByte buffer).
I send files to the printer with 'cat filename > /dev/ttyS1'

The printer is set up for no parity, 9600 baud, rts/cts handshaking,
and that's what I've specified with stty (and this IS set, which I
verified with 'stty -a')

Can somebody tell me what I am doing wrong, or give me any hints?
Or, does anybody know how does initializes the serial port, so that
I can specify exactly the same settings under Linux?

All help appreciated,


| Message is author's opinion only |
|                                  |
| Andries Kruithof                 |
| Schlumberger Geco-Prakla         |



1. Mgetty and Solaris 8 serial port initialization

I have installed the mgetty package on one of my Solaris boxes
to allow me to utilize my fax-modem to receive both faxes as well
as data calls on the modem line.  It really does work great.
However, after a system reboot, mgetty (which is spawned directly
from /etc/inittab like gettys of old) complains that it cannot
open the line and respawns several times before settling down:

01/13 16:23:34 a/b  mod: cannot open line /dev/cua/b: Device busy
01/13 16:23:34 a/b  open device /dev/cua/b failed: Device busy
01/13 16:23:34 a/b  cannot get terminal line dev=cua/b, exiting: Device busy

The following line has been added to the end of /etc/inittab to
invoke it:

mg:34:respawn:/usr/local/sbin/mgetty cua/b

I'm theorizing that the underlying problem is that the serial port
is not yet initialized at the time mgetty is first invoked.  I
understand that several stream modules must be pushed for the port
to look like a serial port.

My question is:  Who does this?  ttymon?  How can one tell when it
has been accomplished?  Or, am I all wet and the problem is not
related to this at all?

Thanks in advance,

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