From jbye@acorn.co.uk Wed Jan 27 18:20:55 1993
From: jbye@acorn.co.uk (James)
Newsgroups: comp.sys.acorn
Subject: Re: Joystick SWIs
Date: 14 Jul 92 07:33:50 GMT
Organization: Acorn Computers Ltd, Cambridge, England

In article <1992Jul13.144102.29178@cs.nott.ac.uk> smb@cs.nott.ac.uk (Simon Burrows) writes:

>
>I would be most grateful if some kind person could post details of the
>official Acorn joystick SWIs. I am developing some software, and it would
>be most foolish not to incorporate support for the Acorn SWIs.
>
>Thanks in advance,
>
>Simon.


And just to be a kind person, here is the documentation attached on the end
of this posting.

--James

----------------- 8< cut here 8< ---------------------------------------

SWI Interface for Joystick Devices
----------------------------------

The Joystick module provides a SWI interface for reading the state of a
joystick.  When the module  initialises, it tests for the existence of
built-in joystick hardware and if it does not find any then it will not 
initialise.  Third parties can replace this module to provide support for
different hardware.  It is  recommended that any such modules have version
numbers greater than 2.00 so that Acorn can upgrade its  own module without
preventing its replacement.       


SWI  Joystick_Read (SWI &43F40)
-------------------------------

Returns the state of a joystick.

On entry:               R0 = joystick number

On exit:                R0 = joystick state

Interrupts:             Interrupt status is not altered

Processor mode:         Processor is in SVC mode

Re-entrancy:            Not defined

Use:                    This SWI is used to obtain the state of the requested
                        joystick.  The state is returned in the following
                        format:

                        Byte 0:         signed Y value (range -127 to 127)
                                        -64, 0 or 64 for single switch joystick
                                        (corresponds to Down, Rest, Up).

                        Byte 1:         signed X value (range -127 to 127)
                                        -64, 0 or 64 for single switch joystick
                                        (corresponds to Left, Rest, Right).

                        Byte 2:         Switches (e.g. fire buttons) starting in
                                        bit 0, unimplemented switches return 0.

                        Byte 3:  Reserved.

Note that this format allows both digital and analogue devices to be
supported.  Applications which are only  interested in state (up, down,
left, right) should not simply test the bytes for positive, negative or
zero.  It is  recommended that the 'at rest' state should span a middle
range, say from -32 to 32 since analogue joysticks  cannot be relied upon to
produce 0 when at rest.