From: Christoph Kukulies <kuku AT gilberto DOT physik DOT rwth-aachen DOT de>
Message-Id: <199703110907.KAA06763@gilberto.physik.rwth-aachen.de>
Subject: Re: joystick reading (gameport)
In-Reply-To: <EMRC0HAVZCJzEw8n@talula.demon.co.uk> from Shawn Hargreaves at "Mar 10, 97 03:18:45 pm"
To: Shawn AT talula DOT demon DOT co DOT uk (Shawn Hargreaves)
Date: Tue, 11 Mar 1997 10:07:43 +0100 (MET)
Cc: djgpp AT delorie DOT com
Reply-To: Christoph Kukulies <kuku AT gilberto DOT physik DOT rwth-aachen DOT de>
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> Christoph Kukulies writes:
> >I found that the inport for the joystick - I want to use it to
> >position my XYZ-stepper motor assembly - is 0x201 and reading
> >using inportb(0x201) gives me the fire button statii but where
> >is the data for the stick itself?
> 
> It's a mess :-) The position is read by status bits in 0x201: bit 0 is
> the X axis, bit 1 is the Y axis, and bits 2 and 3 are for the second

Hmm. bits 2 and 3 ?

With the following test program 

#include <stdio.h>
main()
{
  int i;
  while(1){
     outportb(0x201,0xff);
     i=inportb(0x201);
     printf("%02x\r",i);fflush(stdout);
  }
}

I'm getting 0xff when no button is pressed or no stick action is made.
When I press one fire button I'm getting 0xef, the other 0xdf.

This joystick has two fire buttons (Saitek MEGASTICK III, MX-130)
(e.g.: http://www.dbline.it/shtm/jmx-130.htm)

Are the two fire buttons equivalent to the second joystick?
Why do I see no data in the first nibble?


> joystick. You write a byte to 0x201 (any value), which sets these bits
> to 1, and then time how long they take to fall back to 0. How to
> interpret the results depends on the type of joystick, so you need to
> calibrate it before use, by measuring the time with the joystick in some
> known positions.
> 
> Allegro has some code that does all this: look in joystick.c and misc.s.
> 
> >Sorry, I'm a nono on DOS game programming.  Are there int13/21 
> >calls for reading the joystick information and should I use them
> >better over direct I/O statements?
> 
> There are (I can't remember the details offhand: look in Ralph Brown's
> Interrupt List), but they are only supported by a few BIOS's. You might
> be lucky, which is fine if you only care about your program running on
> your machine, but they haven't been implemented on the last couple of
> systems I tried.
> 
> >Should I take care for contact bouncing, when reading the data?
> 
> Depends on the stick. Some (the more expensive ones) are ok, but on most
> the buttons will bounce a few times. And the position can wobble quite a
> bit, and doesn't always centre itself to the same place. The things are
> a real pain...
> 
> Check out the PCGPE (on x2ftp.oulu.fi) for more info.
> 
> 
> /*
>  *  Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
>  *  Beauty is a French phonetic corruption of a short cloth neck ornament.
>  */
> 

--
Chris Christoph P. U. Kukulies kuku AT gil DOT physik DOT rwth-aachen DOT de