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Input: convert joystick-api doc into ReST format 

This file require some adjustments to be a valid ReST file.
Do it, in order to be able to parse it with Sphinx.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
This commit is contained in:
Mauro Carvalho Chehab 2017-04-04 17:44:38 -07:00 committed by Dmitry Torokhov
parent 1c4ada609d
commit 0498b4b400
1 changed files with 75 additions and 63 deletions
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138
Documentation/input/joystick-api.txt
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@ -1,12 +1,11 @@
Joystick API Documentation -*-Text-*- ==========================
Joystick API Documentation
==========================
Ragnar Hojland Espinosa :Author: Ragnar Hojland Espinosa <ragnar@macula.net> - 7 Aug 1998
<ragnar@macula.net>
7 Aug 1998 Initialization
==============
1. Initialization
~~~~~~~~~~~~~~~~~
Open the joystick device following the usual semantics (that is, with open). Open the joystick device following the usual semantics (that is, with open).
Since the driver now reports events instead of polling for changes, Since the driver now reports events instead of polling for changes,
@ -14,18 +13,20 @@ immediately after the open it will issue a series of synthetic events
(JS_EVENT_INIT) that you can read to check the initial state of the (JS_EVENT_INIT) that you can read to check the initial state of the
joystick. 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); int fd = open ("/dev/input/js0", O_RDONLY);
2. Event Reading Event Reading
~~~~~~~~~~~~~~~~ =============
::
struct js_event e; struct js_event e;
read (fd, &e, sizeof(e)); read (fd, &e, sizeof(e));
where js_event is defined as where js_event is defined as::
struct js_event { struct js_event {
__u32 time; /* event timestamp in milliseconds */ __u32 time; /* event timestamp in milliseconds */
@ -38,10 +39,10 @@ If the read is successful, it will return sizeof(e), unless you wanted to read
more than one event per read as described in section 3.1. 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_BUTTON 0x01 /* button pressed/released */
#define JS_EVENT_AXIS 0x02 /* joystick moved */ #define JS_EVENT_AXIS 0x02 /* joystick moved */
@ -49,47 +50,50 @@ The possible values of ``type'' are
As mentioned above, the driver will issue synthetic JS_EVENT_INIT ORed 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 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 */ int type = JS_EVENT_BUTTON | JS_EVENT_INIT; /* 0x81 */
If you choose not to differentiate between synthetic or real events 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 */ 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 generated the event. Note that they carry separate numeration (that
is, you have both an axis 0 and a button 0). Generally, is, you have both an axis 0 and a button 0). Generally,
number =============== =======
Axis number
=============== =======
1st Axis X 0 1st Axis X 0
1st Axis Y 1 1st Axis Y 1
2nd Axis X 2 2nd Axis X 2
2nd Axis Y 3 2nd Axis Y 3
...and so on ...and so on
=============== =======
Hats vary from one joystick type to another. Some can be moved in 8 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 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. 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 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). 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. button event is 0.
Though this Though this::
if (js_event.type == JS_EVENT_BUTTON) { if (js_event.type == JS_EVENT_BUTTON) {
buttons_state ^= (1 << js_event.number); buttons_state ^= (1 << js_event.number);
@ -97,6 +101,8 @@ Though this
may work well if you handle JS_EVENT_INIT events separately, may work well if you handle JS_EVENT_INIT events separately,
::
if ((js_event.type & ~JS_EVENT_INIT) == JS_EVENT_BUTTON) { if ((js_event.type & ~JS_EVENT_INIT) == JS_EVENT_BUTTON) {
if (js_event.value) if (js_event.value)
buttons_state |= (1 << js_event.number); buttons_state |= (1 << js_event.number);
@ -109,17 +115,17 @@ have to write a separate handler for JS_EVENT_INIT events in the first
snippet, this ends up being shorter. 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 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 task of detecting double clicks, figuring out if movement of axis and button
presses happened at the same time, and similar. 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, 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 wait) forever until an event is generated and effectively read. There
@ -133,8 +139,8 @@ admittedly, a long time;)
b) open the device in non-blocking mode (O_NONBLOCK) 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 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 necessarily a "real" error (check errno(3)); it can just mean there
@ -143,6 +149,8 @@ all events on the queue (that is, until you get a -1).
For example, For example,
::
while (1) { while (1) {
while (read (fd, &e, sizeof(e)) > 0) { while (read (fd, &e, sizeof(e)) > 0) {
process_event (e); process_event (e);
@ -171,14 +179,17 @@ the driver will switch to startup mode and next time you read it,
synthetic events (JS_EVENT_INIT) will be generated to inform you of synthetic events (JS_EVENT_INIT) will be generated to inform you of
the actual state of the joystick. 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 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 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 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]; struct js_event mybuffer[0xff];
int i = read (fd, mybuffer, sizeof(mybuffer)); int i = read (fd, mybuffer, sizeof(mybuffer));
@ -189,10 +200,10 @@ sizeof(js_event) Again, if the buffer was full, it's a good idea to
process the events and keep reading it until you empty the driver queue. 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 */ /* function 3rd arg */
#define JSIOCGAXES /* get number of axes char */ #define JSIOCGAXES /* get number of axes char */
@ -202,31 +213,31 @@ The joystick driver defines the following ioctl(2) operations.
#define JSIOCSCORR /* set correction values &js_corr */ #define JSIOCSCORR /* set correction values &js_corr */
#define JSIOCGCORR /* get 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; char number_of_axes;
ioctl (fd, JSIOCGAXES, &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 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 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 IOCTL will fail. For a compile-time decision, you can test the
JS_VERSION symbol JS_VERSION symbol::
#ifdef JS_VERSION #ifdef JS_VERSION
#if JS_VERSION > 0xsomething #if JS_VERSION > 0xsomething
4.2 JSIOCGNAME JSIOCGNAME
~~~~~~~~~~~~~~ ----------
JSIOCGNAME(len) allows you to get the name string of the joystick - the same 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 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 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]; char name[128];
if (ioctl(fd, JSIOCGNAME(sizeof(name)), name) < 0) if (ioctl(fd, JSIOCGNAME(sizeof(name)), name) < 0)
@ -234,8 +245,8 @@ possible overrun should the name be too long.
printf("Name: %s\n", name); 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 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 not needed in a normal program, only in joystick calibration software
@ -246,7 +257,7 @@ warning in following releases of the driver.
Both JSIOCSCORR and JSIOCGCORR expect &js_corr to be able to hold Both JSIOCSCORR and JSIOCGCORR expect &js_corr to be able to hold
information for all axis. That is, struct js_corr corr[MAX_AXIS]; 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 { struct js_corr {
__s32 coef[8]; __s32 coef[8];
@ -254,17 +265,17 @@ struct js_corr is defined as
__u16 type; __u16 type;
}; };
and ``type'' and ``type``::
#define JS_CORR_NONE 0x00 /* returns raw values */ #define JS_CORR_NONE 0x00 /* returns raw values */
#define JS_CORR_BROKEN 0x01 /* broken line */ #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 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; struct JS_DATA_TYPE js;
while (1) { while (1) {
@ -275,7 +286,7 @@ The driver offers backward compatibility, though. Here's a quick summary:
} }
As you can figure out from the example, the read returns immediately, 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 { struct JS_DATA_TYPE {
int buttons; /* immediate button state */ int buttons; /* immediate button state */
@ -283,12 +294,14 @@ with the actual state of the joystick.
int y; /* immediate y axis value */ 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) #define JS_RETURN sizeof(struct JS_DATA_TYPE)
To test the state of the buttons, To test the state of the buttons,
::
first_button_state = js.buttons & 1; first_button_state = js.buttons & 1;
second_button_state = js.buttons & 2; second_button_state = js.buttons & 2;
@ -302,13 +315,12 @@ called Multisystem joysticks in this driver), under /dev/djsX. This driver
doesn't try to be compatible with that interface. 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 ____/| Comments, additions, and specially corrections are welcome.
EOF \ 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 ;)