@@ -1,12 +1,16 @@
-Force feedback for Linux.
-By Johann Deneux <johann.deneux@gmail.com> on 2001/04/22.
-Updated by Anssi Hannula <anssi.hannula@gmail.com> on 2006/04/09.
+========================
+Force feedback for Linux
+========================
+
+:Author: Johann Deneux <johann.deneux@gmail.com> on 2001/04/22.
+:Updated: Anssi Hannula <anssi.hannula@gmail.com> on 2006/04/09.
+
You may redistribute this file. Please remember to include shape.fig and
interactive.fig as well.
-----------------------------------------------------------------------------
-1. Introduction
-~~~~~~~~~~~~~~~
+Introduction
+~~~~~~~~~~~~
+
This document describes how to use force feedback devices under Linux. The
goal is not to support these devices as if they were simple input-only devices
(as it is already the case), but to really enable the rendering of force
@@ -15,8 +19,9 @@ This document only describes the force feedback part of the Linux input
interface. Please read joystick.txt and input.txt before reading further this
document.
-2. Instructions to the user
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Instructions to the user
+~~~~~~~~~~~~~~~~~~~~~~~~
+
To enable force feedback, you have to:
1. have your kernel configured with evdev and a driver that supports your
@@ -33,39 +38,48 @@ something goes wrong.
If you have a serial iforce device, you need to start inputattach. See
joystick.txt for details.
-2.1 Does it work ?
-~~~~~~~~~~~~~~~~~~
-There is an utility called fftest that will allow you to test the driver.
-% fftest /dev/input/eventXX
+Does it work ?
+--------------
+
+There is an utility called fftest that will allow you to test the driver::
+
+ % fftest /dev/input/eventXX
+
+Instructions to the developer
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-3. Instructions to the developer
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
All interactions are done using the event API. That is, you can use ioctl()
and write() on /dev/input/eventXX.
This information is subject to change.
-3.1 Querying device capabilities
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-#include <linux/input.h>
-#include <sys/ioctl.h>
+Querying device capabilities
+----------------------------
-#define BITS_TO_LONGS(x) \
- (((x) + 8 * sizeof (unsigned long) - 1) / (8 * sizeof (unsigned long)))
-unsigned long features[BITS_TO_LONGS(FF_CNT)];
-int ioctl(int file_descriptor, int request, unsigned long *features);
+::
+
+ #include <linux/input.h>
+ #include <sys/ioctl.h>
+
+ #define BITS_TO_LONGS(x) \
+ (((x) + 8 * sizeof (unsigned long) - 1) / (8 * sizeof (unsigned long)))
+ unsigned long features[BITS_TO_LONGS(FF_CNT)];
+ int ioctl(int file_descriptor, int request, unsigned long *features);
"request" must be EVIOCGBIT(EV_FF, size of features array in bytes )
Returns the features supported by the device. features is a bitfield with the
following bits:
+
- FF_CONSTANT can render constant force effects
- FF_PERIODIC can render periodic effects with the following waveforms:
+
- FF_SQUARE square waveform
- FF_TRIANGLE triangle waveform
- FF_SINE sine waveform
- FF_SAW_UP sawtooth up waveform
- FF_SAW_DOWN sawtooth down waveform
- FF_CUSTOM custom waveform
+
- FF_RAMP can render ramp effects
- FF_SPRING can simulate the presence of a spring
- FF_FRICTION can simulate friction
@@ -75,24 +89,30 @@ following bits:
- FF_GAIN gain is adjustable
- FF_AUTOCENTER autocenter is adjustable
-Note: In most cases you should use FF_PERIODIC instead of FF_RUMBLE. All
+.. note::
+
+ - In most cases you should use FF_PERIODIC instead of FF_RUMBLE. All
devices that support FF_RUMBLE support FF_PERIODIC (square, triangle,
sine) and the other way around.
-Note: The exact syntax FF_CUSTOM is undefined for the time being as no driver
+ - The exact syntax FF_CUSTOM is undefined for the time being as no driver
supports it yet.
+::
-int ioctl(int fd, EVIOCGEFFECTS, int *n);
+ int ioctl(int fd, EVIOCGEFFECTS, int *n);
Returns the number of effects the device can keep in its memory.
-3.2 Uploading effects to the device
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-#include <linux/input.h>
-#include <sys/ioctl.h>
+Uploading effects to the device
+-------------------------------
-int ioctl(int file_descriptor, int request, struct ff_effect *effect);
+::
+
+ #include <linux/input.h>
+ #include <sys/ioctl.h>
+
+ int ioctl(int file_descriptor, int request, struct ff_effect *effect);
"request" must be EVIOCSFF.
@@ -110,34 +130,41 @@ See <linux/input.h> for a description of the ff_effect struct. You should also
find help in a few sketches, contained in files shape.fig and interactive.fig.
You need xfig to visualize these files.
-3.3 Removing an effect from the device
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-int ioctl(int fd, EVIOCRMFF, effect.id);
+
+Removing an effect from the device
+----------------------------------
+
+::
+
+ int ioctl(int fd, EVIOCRMFF, effect.id);
This makes room for new effects in the device's memory. Note that this also
stops the effect if it was playing.
-3.4 Controlling the playback of effects
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Controlling the playback of effects
+-----------------------------------
+
Control of playing is done with write(). Below is an example:
-#include <linux/input.h>
-#include <unistd.h>
+::
+
+ #include <linux/input.h>
+ #include <unistd.h>
struct input_event play;
struct input_event stop;
struct ff_effect effect;
int fd;
-...
+ ...
fd = open("/dev/input/eventXX", O_RDWR);
-...
+ ...
/* Play three times */
play.type = EV_FF;
play.code = effect.id;
play.value = 3;
write(fd, (const void*) &play, sizeof(play));
-...
+ ...
/* Stop an effect */
stop.type = EV_FF;
stop.code = effect.id;
@@ -145,43 +172,50 @@ Control of playing is done with write(). Below is an example:
write(fd, (const void*) &play, sizeof(stop));
-3.5 Setting the gain
-~~~~~~~~~~~~~~~~~~~~
+Setting the gain
+----------------
+
Not all devices have the same strength. Therefore, users should set a gain
factor depending on how strong they want effects to be. This setting is
persistent across access to the driver.
-/* Set the gain of the device
-int gain; /* between 0 and 100 */
-struct input_event ie; /* structure used to communicate with the driver */
+::
-ie.type = EV_FF;
-ie.code = FF_GAIN;
-ie.value = 0xFFFFUL * gain / 100;
+ /* Set the gain of the device
+ int gain; /* between 0 and 100 */
+ struct input_event ie; /* structure used to communicate with the driver */
-if (write(fd, &ie, sizeof(ie)) == -1)
+ ie.type = EV_FF;
+ ie.code = FF_GAIN;
+ ie.value = 0xFFFFUL * gain / 100;
+
+ if (write(fd, &ie, sizeof(ie)) == -1)
perror("set gain");
-3.6 Enabling/Disabling autocenter
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Enabling/Disabling autocenter
+-----------------------------
+
The autocenter feature quite disturbs the rendering of effects in my opinion,
and I think it should be an effect, which computation depends on the game
type. But you can enable it if you want.
-int autocenter; /* between 0 and 100 */
-struct input_event ie;
+::
-ie.type = EV_FF;
-ie.code = FF_AUTOCENTER;
-ie.value = 0xFFFFUL * autocenter / 100;
+ int autocenter; /* between 0 and 100 */
+ struct input_event ie;
-if (write(fd, &ie, sizeof(ie)) == -1)
+ ie.type = EV_FF;
+ ie.code = FF_AUTOCENTER;
+ ie.value = 0xFFFFUL * autocenter / 100;
+
+ if (write(fd, &ie, sizeof(ie)) == -1)
perror("set auto-center");
A value of 0 means "no auto-center".
-3.7 Dynamic update of an effect
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Dynamic update of an effect
+---------------------------
+
Proceed as if you wanted to upload a new effect, except that instead of
setting the id field to -1, you set it to the wanted effect id.
Normally, the effect is not stopped and restarted. However, depending on the
@@ -192,30 +226,32 @@ case, the driver stops the effect, up-load it, and restart it.
Therefore it is recommended to dynamically change direction while the effect
is playing only when it is ok to restart the effect with a replay count of 1.
-3.8 Information about the status of effects
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+Information about the status of effects
+---------------------------------------
+
Every time the status of an effect is changed, an event is sent. The values
-and meanings of the fields of the event are as follows:
+and meanings of the fields of the event are as follows::
-struct input_event {
-/* When the status of the effect changed */
- struct timeval time;
+ struct input_event {
+ /* When the status of the effect changed */
+ struct timeval time;
-/* Set to EV_FF_STATUS */
- unsigned short type;
+ /* Set to EV_FF_STATUS */
+ unsigned short type;
-/* Contains the id of the effect */
- unsigned short code;
+ /* Contains the id of the effect */
+ unsigned short code;
-/* Indicates the status */
- unsigned int value;
-};
+ /* Indicates the status */
+ unsigned int value;
+ };
-FF_STATUS_STOPPED The effect stopped playing
-FF_STATUS_PLAYING The effect started to play
+ FF_STATUS_STOPPED The effect stopped playing
+ FF_STATUS_PLAYING The effect started to play
-NOTE: Status feedback is only supported by iforce driver. If you have
+.. note::
+
+ - Status feedback is only supported by iforce driver. If you have
a really good reason to use this, please contact
linux-joystick@atrey.karlin.mff.cuni.cz or anssi.hannula@gmail.com
so that support for it can be added to the rest of the drivers.
-
This file require minimum 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> --- Documentation/input/ff.txt | 188 +++++++++++++++++++++++++++------------------ 1 file changed, 112 insertions(+), 76 deletions(-)