Re: trapping the STOP key in an IRQ

From: Marko Mäkelä <>
Date: Thu, 24 Apr 2014 08:50:41 +0300
Message-ID: <20140424055041.GA4064@x220>
On Wed, Apr 23, 2014 at 10:32:02AM -0400, Charlie Hitselberger wrote:
>What I would like to do is use the STOP button as an escape key for 
>editor commands.

Could you modify the editor input loop that is waiting for a keypress?  
The STOP button should emit the code 3 (ctrl-c) when using jsr $ffe4.

If you want to handle the STOP key in the IRQ handler, I believe that 
you would have to add some kind of counter and a global variable that is 
shared between the IRQ handler and the event loop.

>I would like to flash the screen (EOR #$80, wait 5 jiffies, EOR #$80) 
>when the user hits STOP.  The PET will go into a loop waiting for the 
>next keystroke and treat it as an editor command.  I don't want the 
>screen to flash 137 times when the user holds down the STOP key, I only 
>want to notice and react once to each discrete STOP key press and 
>release event pair.  Any ideas?

Is the STOP key auto-repeating on the PET? Even if it were, your input 
loop could skip the screen-flashing if the previously received key code 
was 3.

However, if I were you, I would define STOP+STOP as a "cancel the 
escape" command. Pressing STOP once would invert the screen (first 
EOR#$80), and pressing STOP again would invert it back. Also, any valid 
STOP+x combination would invert the screen back.


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Received on 2014-04-24 06:00:08

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