- Joystick API Documentation -*-Text-*-
+==========================
+Joystick API Documentation
+==========================
- Ragnar Hojland Espinosa
- <ragnar@macula.net>
+:Author: Ragnar Hojland Espinosa <ragnar@macula.net> - 7 Aug 1998
- 7 Aug 1998
-
-1. Initialization
-~~~~~~~~~~~~~~~~~
+Initialization
+==============
Open the joystick device following the usual semantics (that is, with open).
Since the driver now reports events instead of polling for changes,
(JS_EVENT_INIT) that you can read to check the initial state of the
joystick.
-By default, the device is opened in blocking mode.
+By default, the device is opened in blocking mode::
int fd = open ("/dev/input/js0", O_RDONLY);
-2. Event Reading
-~~~~~~~~~~~~~~~~
+Event Reading
+=============
+
+::
struct js_event e;
read (fd, &e, sizeof(e));
-where js_event is defined as
+where js_event is defined as::
struct js_event {
__u32 time; /* event timestamp in milliseconds */
more than one event per read as described in section 3.1.
-2.1 js_event.type
-~~~~~~~~~~~~~~~~~
+js_event.type
+-------------
-The possible values of ``type'' are
+The possible values of ``type`` are::
#define JS_EVENT_BUTTON 0x01 /* button pressed/released */
#define JS_EVENT_AXIS 0x02 /* joystick moved */
As mentioned above, the driver will issue synthetic JS_EVENT_INIT ORed
events on open. That is, if it's issuing a INIT BUTTON event, the
-current type value will be
+current type value will be::
int type = JS_EVENT_BUTTON | JS_EVENT_INIT; /* 0x81 */
If you choose not to differentiate between synthetic or real events
-you can turn off the JS_EVENT_INIT bits
+you can turn off the JS_EVENT_INIT bits::
type &= ~JS_EVENT_INIT; /* 0x01 */
-2.2 js_event.number
-~~~~~~~~~~~~~~~~~~~
+js_event.number
+---------------
-The values of ``number'' correspond to the axis or button that
+The values of ``number`` correspond to the axis or button that
generated the event. Note that they carry separate numeration (that
is, you have both an axis 0 and a button 0). Generally,
- number
+ =============== =======
+ Axis number
+ =============== =======
1st Axis X 0
1st Axis Y 1
2nd Axis X 2
2nd Axis Y 3
...and so on
+ =============== =======
Hats vary from one joystick type to another. Some can be moved in 8
directions, some only in 4, The driver, however, always reports a hat as two
independent axis, even if the hardware doesn't allow independent movement.
-2.3 js_event.value
-~~~~~~~~~~~~~~~~~~
+js_event.value
+--------------
-For an axis, ``value'' is a signed integer between -32767 and +32767
+For an axis, ``value`` is a signed integer between -32767 and +32767
representing the position of the joystick along that axis. If you
-don't read a 0 when the joystick is `dead', or if it doesn't span the
+don't read a 0 when the joystick is ``dead``, or if it doesn't span the
full range, you should recalibrate it (with, for example, jscal).
-For a button, ``value'' for a press button event is 1 and for a release
+For a button, ``value`` for a press button event is 1 and for a release
button event is 0.
-Though this
+Though this::
if (js_event.type == JS_EVENT_BUTTON) {
buttons_state ^= (1 << js_event.number);
may work well if you handle JS_EVENT_INIT events separately,
+::
+
if ((js_event.type & ~JS_EVENT_INIT) == JS_EVENT_BUTTON) {
if (js_event.value)
buttons_state |= (1 << js_event.number);
snippet, this ends up being shorter.
-2.4 js_event.time
-~~~~~~~~~~~~~~~~~
+js_event.time
+-------------
-The time an event was generated is stored in ``js_event.time''. It's a time
+The time an event was generated is stored in ``js_event.time``. It's a time
in milliseconds since ... well, since sometime in the past. This eases the
task of detecting double clicks, figuring out if movement of axis and button
presses happened at the same time, and similar.
-3. Reading
-~~~~~~~~~~
+Reading
+=======
If you open the device in blocking mode, a read will block (that is,
wait) forever until an event is generated and effectively read. There
b) open the device in non-blocking mode (O_NONBLOCK)
-3.1 O_NONBLOCK
-~~~~~~~~~~~~~~
+O_NONBLOCK
+----------
If read returns -1 when reading in O_NONBLOCK mode, this isn't
necessarily a "real" error (check errno(3)); it can just mean there
For example,
+::
+
while (1) {
while (read (fd, &e, sizeof(e)) > 0) {
process_event (e);
synthetic events (JS_EVENT_INIT) will be generated to inform you of
the actual state of the joystick.
-[As for version 1.2.8, the queue is circular and able to hold 64
+
+.. note::
+
+ As for version 1.2.8, the queue is circular and able to hold 64
events. You can increment this size bumping up JS_BUFF_SIZE in
- joystick.h and recompiling the driver.]
+ joystick.h and recompiling the driver.
In the above code, you might as well want to read more than one event
at a time using the typical read(2) functionality. For that, you would
-replace the read above with something like
+replace the read above with something like::
struct js_event mybuffer[0xff];
int i = read (fd, mybuffer, sizeof(mybuffer));
process the events and keep reading it until you empty the driver queue.
-4. IOCTLs
-~~~~~~~~~
+IOCTLs
+======
-The joystick driver defines the following ioctl(2) operations.
+The joystick driver defines the following ioctl(2) operations::
/* function 3rd arg */
#define JSIOCGAXES /* get number of axes char */
#define JSIOCSCORR /* set correction values &js_corr */
#define JSIOCGCORR /* get correction values &js_corr */
-For example, to read the number of axes
+For example, to read the number of axes::
char number_of_axes;
ioctl (fd, JSIOCGAXES, &number_of_axes);
-4.1 JSIOGCVERSION
-~~~~~~~~~~~~~~~~~
+JSIOGCVERSION
+-------------
JSIOGCVERSION is a good way to check in run-time whether the running
driver is 1.0+ and supports the event interface. If it is not, the
IOCTL will fail. For a compile-time decision, you can test the
-JS_VERSION symbol
+JS_VERSION symbol::
#ifdef JS_VERSION
#if JS_VERSION > 0xsomething
-4.2 JSIOCGNAME
-~~~~~~~~~~~~~~
+JSIOCGNAME
+----------
JSIOCGNAME(len) allows you to get the name string of the joystick - the same
as is being printed at boot time. The 'len' argument is the length of the
buffer provided by the application asking for the name. It is used to avoid
-possible overrun should the name be too long.
+possible overrun should the name be too long::
char name[128];
if (ioctl(fd, JSIOCGNAME(sizeof(name)), name) < 0)
printf("Name: %s\n", name);
-4.3 JSIOC[SG]CORR
-~~~~~~~~~~~~~~~~~
+JSIOC[SG]CORR
+-------------
For usage on JSIOC[SG]CORR I suggest you to look into jscal.c They are
not needed in a normal program, only in joystick calibration software
Both JSIOCSCORR and JSIOCGCORR expect &js_corr to be able to hold
information for all axis. That is, struct js_corr corr[MAX_AXIS];
-struct js_corr is defined as
+struct js_corr is defined as::
struct js_corr {
__s32 coef[8];
__u16 type;
};
-and ``type''
+and ``type``::
#define JS_CORR_NONE 0x00 /* returns raw values */
#define JS_CORR_BROKEN 0x01 /* broken line */
-5. Backward compatibility
-~~~~~~~~~~~~~~~~~~~~~~~~~
+Backward compatibility
+======================
The 0.x joystick driver API is quite limited and its usage is deprecated.
-The driver offers backward compatibility, though. Here's a quick summary:
+The driver offers backward compatibility, though. Here's a quick summary::
struct JS_DATA_TYPE js;
while (1) {
}
As you can figure out from the example, the read returns immediately,
-with the actual state of the joystick.
+with the actual state of the joystick::
struct JS_DATA_TYPE {
int buttons; /* immediate button state */
int y; /* immediate y axis value */
};
-and JS_RETURN is defined as
+and JS_RETURN is defined as::
#define JS_RETURN sizeof(struct JS_DATA_TYPE)
To test the state of the buttons,
+::
+
first_button_state = js.buttons & 1;
second_button_state = js.buttons & 2;
doesn't try to be compatible with that interface.
-6. Final Notes
-~~~~~~~~~~~~~~
+Final Notes
+===========
-____/| Comments, additions, and specially corrections are welcome.
-\ o.O| Documentation valid for at least version 1.2.8 of the joystick
- =(_)= driver and as usual, the ultimate source for documentation is
- U to "Use The Source Luke" or, at your convenience, Vojtech ;)
+::
- - Ragnar
-EOF
+ ____/| Comments, additions, and specially corrections are welcome.
+ \ o.O| Documentation valid for at least version 1.2.8 of the joystick
+ =(_)= driver and as usual, the ultimate source for documentation is
+ U to "Use The Source Luke" or, at your convenience, Vojtech ;)
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