Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!sundc!hadron!jsdy
From: jsdy@hadron.UUCP (Joseph S. D. Yao)
Newsgroups: comp.unix.questions,comp.unix.wizards,comp.lang.c
Subject: Re: Filtering Everything
Message-ID: <521@hadron.UUCP>
Date: Mon, 27-Apr-87 12:19:30 EDT
Article-I.D.: hadron.521
Posted: Mon Apr 27 12:19:30 1987
Date-Received: Tue, 28-Apr-87 01:40:18 EDT
References: <919@watmum.UUCP> <6447@bu-cs.BU.EDU> <3446@rsch.WISC.EDU> <16583@sun.uucp> <3448@rsch.WISC.EDU>
Reply-To: jsdy@hadron.UUCP (Joseph S. D. Yao)
Distribution: comp
Organization: Hadron, Inc., Fairfax, VA
Lines: 26
Summary: Some help, maybe.
Xref: mnetor comp.unix.questions:2048 comp.unix.wizards:2048 comp.lang.c:1912

In article <3448@rsch.WISC.EDU> mcvoy@rsch.WISC.EDU (Larry McVoy) writes:
>I was wondering about this... I've never used sxt's (pc7300 doesn't run 5.3)
>so I don't know what the diffference is.   Can't you use them just like
>ptty's?  If I wanted to write an application that preprocesses tty input
>but is transparent to applications underneath it, can I do that?

Sxt's are an attempt to use the xt driver (for the blit / tty5620) for
other purposes.  It is  n o t  a general-purpose pty driver.  On the
BLIT, it is used to have one TTY port mapped to <= 7 windows.  What
happens is that xt000 (xt/000) is the control xt, and the other seven
(or six, I'm not 100% sure) are used to attach to different processes
in the different windows.  Similarly, with the sxt driver and shl
(which is the s5 "job control" shell), you have shl attached to sxt/000
and the processes attached to sxt/00[1-7].  The next shl takes sxt/01?,
etc.  You may not shl (or run layers on a blit) unless you are actually
on an interactive tty; which means that if you are on an xt or sxt (a
layer or shl sub-shell), then you can't re-shl to get another layer of
sub-shells, so you are limited to seven! (six?)  Curiously, on the VAX
11/7??, the console terminal was NOT considered an interactive tty, as
it was a subdriver of the front-end-processor driver!  (I modified both
xt and sxt drivers to understand that it really was kosher.)

	Joe Yao		jsdy@hadron.COM (not yet domainised)
	hadron!jsdy@{seismo.CSS.GOV,dtix.ARPA,decuac.DEC.COM}
{arinc,att,avatar,cos,decuac,dtix,ecogong,kcwc}!hadron!jsdy
     {netex,netxcom,rlgvax,seismo,smsdpg,sundc}!hadron!jsdy