Path: utzoo!attcan!uunet!wuarchive!zaphod.mps.ohio-state.edu!samsung!umich!sharkey!cfctech!teemc!fmeed1!wehr
From: wehr@fmeed1.UUCP (Bruce Wehr)
Newsgroups: comp.sys.hp
Subject: Re: stty on hp9000s300
Summary: This is just a guess, but ...
Message-ID: <7947@fmeed1.UUCP>
Date: 12 Sep 90 15:33:17 GMT
References: <1990Sep11.155337.17413@cunixf.cc.columbia.edu>
Organization: Ford Electronics Division, Dearborn MI
Lines: 36

In article <1990Sep11.155337.17413@cunixf.cc.columbia.edu>, puglia@cunixf.cc.columbia.edu (Paul Puglia) writes:
> 
> Could some please tell me why stty [some mode] < /dev/tty?? doesn't
> work under hp-ux 7.0.

This is just a guess, but here goes.  When no process has a serial line
open, its stty values are undefined.  When the first process opens a
serial line, the values are set to defaults (300 baud, cs8, etc..).  Any
changes that occur will remain in effect *only* while some process has
the file open.

I think what's happening to you is this:  when you say "stty foo
</dev/ttybar", the shell forks, opens the line (the default values are
put into effect), and then execs an stty.  The stty then changes the
values you requested.  That being done, the stty process exits, the line
is closed, and the changes are lost.

Your fix is this:  start a process that will keep the line open.
Something like "nohup sleep 200000000 </dev/ttybar &".  This will open
the line, set the default values, and *keep the line open*.  Any
subsequent changes you do with an "stty foo </dev/ttybar" will remain in
effect.

If this looks familiar, it's because HP has this line as an option in
/etc/rc, used for exactly that purpose:  to set the baud rate for a
serial printer, and keep it that way.  I learned about this mechanism by
trying to figure out why anybody would be as "stupid" as nohupping an
effectively never-ending sleep in the background.

Hope this helps.

-- 
	       Bruce Wehr (wehr%dptc.decnet@srlvx0.srl.ford.com)
 (...uunet!mailrus!sharkey!fmeed1!wehr) (wehr%fmeed1.uucp@mailgw.cc.umich.edu)
		   Ford Motor Company - Electronics Division
  17000 Rotunda Drive, ETC Room LN081, Dearborn, Michigan 48121 (313)845-3039