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From: kneller@cgl.ucsf.edu (Don Kneller)
Newsgroups: comp.sys.ibm.pc
Subject: Re: ^P locks up keyboard
Message-ID: <10495@cgl.ucsf.EDU>
Date: Wed, 11-Nov-87 17:37:16 EST
Article-I.D.: cgl.10495
Posted: Wed Nov 11 17:37:16 1987
Date-Received: Sat, 14-Nov-87 04:06:16 EST
References: <15000045@silver> <753@pilchuck.Data-IO.COM>
Sender: daemon@cgl.ucsf.edu
Reply-To: kneller@socrates.ucsf.edu.UUCP (Don Kneller)
Organization: UCSF Computer Graphics Lab
Lines: 93

In article <753@pilchuck.Data-IO.COM> jgray@toad.pilchuck.Data-IO.COM (Jerry Late Nite Gray) writes:
>In article <15000045@silver>, creps@silver.bacs.indiana.edu writes:
>> 
>> 
>>    This may have been discussed before, but I just noticed it. On
>> DOS 3.21, if I type ^P at the system prompt the cursor moves back
>> to the beginning of the line, and then the keyboard locks up, although
>
>I saw the same thing (sort of) but it usually occured when using ^P within
>Emacs. There was generally no problem until exiting the program and the
>system would lock up. I found out later [...] that this problem occurred
>due to the PC trying to write to a non-existant printer and $##*$&^$#*$&
>DOS not dealing with it in a civilized manner.  Whenever this happens
>now, I just enable the printer and it unlocks the system by generating the
>familiar :
>	Trying to write to device driver
>	Abort, Retry or Ignore:
>
>Of course I have to type "Retry" since anything else will cause whatever
>task I am running to abort (Stupid $#%&^&#%#&^#&%^ OS).
>
>My general question is how can I temporarily suspend the ^P function when
>entering Emacs.



The ^P toggles the "echo output to printer" command, just like ^PrtSc.
With DOS 3.1 (I can't speak for any higher), when the prompt to
"Abort, Retry or Ignore" happens, type ^P (toggling echo off again),
then `I' each time you get reprompted.  After only a few prompts, the
printer buffer will be flushed and you will be back in business.

It is possible to disable ^P (and ^S) with the DOS IOCTL interrupt.
This is used to put the terminal into "raw" mode.  A side affect
of doing this is that output to the screen is sped up quite a bit
(perhaps twice to thrice as fast).  This side affect happens because
DOS no longer checks the input buffer for special characters whenever
it *outputs* to the screen.

Here is a code fragment in C for putting the terminal into raw mode
and for returning it to the default.  This is for Microsoft C but
it is very short and should be easy to modify.

#include <stdio.h>
#include <dos.h>
#define DEVICE	0x80
#define RAW	0x20
#define IOCTL	0x44
#define STDIN	fileno(stdin)
#define STDOUT	fileno(stdout)
#define GETBITS	0
#define SETBITS	1

static unsigned	int old_stdin, old_stdout, ioctl();

void
setraw() {
	old_stdin = ioctl(STDIN, GETBITS, 0);
	old_stdout = ioctl(STDOUT, GETBITS, 0);
	if (old_stdin & DEVICE)
		ioctl(STDIN, SETBITS, old_stdin | RAW);
	if (old_stdout & DEVICE)
		ioctl(STDOUT, SETBITS, old_stdout | RAW);
}

void
unsetraw() {
	if (old_stdin)
		(void) ioctl(STDIN, SETBITS, old_stdin);
	if (old_stdout)
		(void) ioctl(STDOUT, SETBITS, old_stdout);
}

static unsigned int
ioctl(handle, mode, setvalue)
int		handle, mode;
unsigned int	setvalue;
{
	union REGS regs;

	regs.h.ah = IOCTL;
	regs.h.al = (unsigned char) mode;
	regs.x.bx = handle;
	regs.h.dl = (unsigned char) setvalue;
	regs.h.dh = 0;			/* Zero out dh */
	intdos(&regs, &regs);
	return (regs.x.dx);
}
-----
	Don Kneller
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