[ILUG] (en?/dis?)-abling modem-control signals on a (not-open) serial port?

[Michael Watterson]

Brian Foster wrote:
>  I'm running SUSE 9.2 and, for various not-relevant
>  reasons, decided to run the YaST2 init(8) “runlevel”
>  editor.  it hung during its initialisation.  after
>  investigating, I determined the bash(1) command:
>
>    isserial </dev/ttyS1
>
>  is hanging; strace(1) shows the (bash) open(2) of
>  /dev/ttyS1 is hanging.  this isn't too surprising
>  since ttyS1 is the serial modem (and all this was
>  done whilst I was off-line; i.e., that serial port
>  is NOT open, and there is probably no other process
>  trying to open it (and the permissions are not the
>  issue!)).
>
>  after a few false starts, I determined the hang is
>  because the line has _somehow_ been configured to
>  require various modem-control signals (i.e., it's
>  not a simple 3-wire connection).  again, not too
>  surprising (albeit it took me awhile to get to
>  this “obvious” point!  ;-\  ).   the (admittedly
>  unused) non-modem serial port is not so configured.
>
>  but at this point I'm stuck:  how does Linux (2.6)
>  configure a serial port to use (or to not use?)
>  modem-control signals?   this is (now) just for my
>  own curiosity since the original YaST2 problem can
>  be solved by a bit of hacking on the relevant shell
>  script.  I've _no_ intention of changing anything
>  w.r.t. the modem or the serial port; I am (now)
>  simply curious.
>
>  ( apologies if this is described someplace; I've
>   drawn a blank with quick searches for an answer.
>   nor did I spot anything in /etc/init.d/*, albeit
>   it's always possible I missed something? .... )
>
> cheers!
> 	-blf-
>   
There seem to be about 3 incompatible ways of doing this. I remember 
last year figuring this for a PIC based LCD + keypad I programmed as a 
terminal connected to serial port. I wanted keypress level interactive. 
The various examples on net about handshanking and how to disable CR 
input buffer AND have my Linux C programming skip char i/p if no key 
pressed (non-blocking).

I'm using two serial programs currently, one does the Xmodem to my 
latest developemtn board and the other handles screen / terminal 
formatting properly. (KDE).  Minicom does handshake, Xmodem & formating, 
but only with a modem. I set worong serial port and now it exits with error.

Presumably there is a Linux KDE equivalent to MS Hyperterminal for 
serial, that is free and actually does what I want, but I don;t know 
what it is.

Additonally there are three schemes for RS232 hardware handshake wiring, 
using one or two or both schemes of HW signalling,. A Modem can use two 
of them at same time, a Terminal or inter PC only needs either of those 
two, and some serial printers have used a third wiring scheme. Oridinary 
modems never use Xon/Xoff SW handshake.

-- 
Mike