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From: sabi@vax1.acs.udel.EDU (Sabita Nagarajan)
Newsgroups: comp.unix.wizards
Subject: Fast terminal response to keyboard
Keywords: ioctl polling interrupts
Message-ID: <6820@vax1.acs.udel.EDU>
Date: 8 Aug 90 22:36:05 GMT
Organization: University of Delaware
Lines: 54

I have an application which sends large amounts of output to the terminal.
I'd like to be able to stop the output by pressing one key.  To do this, I
have been doing something like this:

    close(0);
    if(open("/dev/tty", O_RDWR | O_NDELAY) == -1) {
        fprintf(stderr, open_error_message);
        exit(1);
    }

    ...

    if(ioctl(0, TCGETA, &tsave) == -1) {
        fprintf(stderr, ioctl_error_message);
        exit(1);
    }

    tchange = tsave;

    tchange.c_lflag &= ~(ICANON | ECHO);
    tchange.c_cc[VMIN] = 1;
    tchange.c_cc[VTIME] = 0;

    if(ioctl(0, TCSETAF, &tchange) == -1) {
        fprintf(stderr, ioctl_error_message);
        exit(1);
    }

    ...

And then to do the read:

    while(TRUE) {
        output_to_terminal();
        c = '\0';
        read(0, &c, 1);
        if(c != '\0')
            exit();
    }

Well, not exactly, but you get the idea.  This is a fairly straightforward
polling scheme, but I notice there's still some slight delay between the
time I press the key and the program exit.  This is especially true on
terminals I have hooked up to standard serial ports (Oops, sorry, I have 
a Wyse 3225 running SCO Xenix 2.3.2 and Computone 16 port board).  I'm
running off the standard ports because it looks like whenever I put the
Computone ports into raw mode, a SIGHUP is generated somehow.  But that's
another question.  My question here is:  How can I get a faster response
from the keyboard?  The output_to_terminal only has to put out a couple of
chars at a time before returning, so it's pretty fast.  What can I do to
speed things up?

Thanks in advance!!
looking for a way to gener