JOY(4)

NAME
joy - games adapter

SYNOPSIS
joy0 at isa? port 0x201
joy* at isapnp?

DESCRIPTION
This driver provides access to the games adapter. The lower bit in the minor device number selects the joystick: 0 is the first joystick and 1 is the second.

The game control adapter allows up to two joysticks to be attached to the system. The adapter plus the driver convert the present resistive value to a relative joystick position. On receipt of an output signal, four timing circuits are started. By determining the time required for the circuit to time-out (a function of the resistance), the paddle position can be determined. The adapter could be used as a general purpose I/O card with four analog (resistive) inputs plus four digital input points.

Applications may call ioctl() on a game adapter driver file descriptor to set and get the offsets of the two potentiometers and the maximum time-out value for the circuit. The ioctl() commands are listed in <machine/joystick.h> and currently are:

JOY_SETTIMEOUT
    Sets the maximum time-out for the adapter.
JOY_GETTIMEOUT
    Returns the current maximum time-out.
JOY_SET_X_OFFSET
    Sets an offset on X value.
JOY_GET_X_OFFSET
    Returns the current X offset.
JOY_SET_Y_OFFSET
    Sets an offset on Y value.
JOY_GET_Y_OFFSET
    Returns the current Y offset.

All of these commands take an integer parameter.

Read() on the file descriptor returns a joystick structure:

    struct joystick {
    	int x;
    	int y;
    	int b1;
    	int b2;
    };

The fields have the following functions:

x   Joystick's current X coordinate (or position of paddle 1).
y   Joystick's current Y coordinate (or position of paddle 2).
b1  Current state of button 1.
b2  Current state of button 2.

The b1 and b2 fields in struct joystick are set to 1 if the corresponding button is down, or 0 otherwise.

The X and Y coordinates are supposed to be between 0 and 255 for a good joystick and a good adapter. Unfortunately, because of the hardware hack that is used to measure the position (by measuring the time needed to discharge an RC circuit made from the joystick's potentiometer and a capacitor on the adapter), calibration is needed to determine exactly what values are returned for a specific joystick/adapter combination. Incorrect hardware can yield negative or > 255 values.

A typical calibration procedure uses the values returned at lower-left, center, and upper-right positions of the joystick to compute the relative position.

This calibration is not part of the driver.

FILES
/dev/joy0
    first joystick
/dev/joy1
    second joystick

SEE ALSO
ioctl(2), intro(4), isa(4), isapnp(4)

AUTHORS
Jean-Marc Zucconi wrote the FreeBSD driver. Matthieu Herrb ported it to OpenBSD and wrote this manual page.