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-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.
-You may redistribute this file. Please remember to include shape.fig and
-interactive.fig as well.
-----------------------------------------------------------------------------
-
-1. 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
-effects.
-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
-~~~~~~~~~~~~~~~~~~~~~~~~~~~
-To enable force feedback, you have to:
-
-1. have your kernel configured with evdev and a driver that supports your
- device.
-2. make sure evdev module is loaded and /dev/input/event* device files are
- created.
-
-Before you start, let me WARN you that some devices shake violently during the
-initialisation phase. This happens for example with my "AVB Top Shot Pegasus".
-To stop this annoying behaviour, move you joystick to its limits. Anyway, you
-should keep a hand on your device, in order to avoid it to break down if
-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
-
-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>
-
-#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
-- FF_DAMPER can simulate damper effects
-- FF_RUMBLE rumble effects
-- FF_INERTIA can simulate inertia
-- FF_GAIN gain is adjustable
-- FF_AUTOCENTER autocenter is adjustable
-
-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
- supports it yet.
-
-
-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>
-
-int ioctl(int file_descriptor, int request, struct ff_effect *effect);
-
-"request" must be EVIOCSFF.
-
-"effect" points to a structure describing the effect to upload. The effect is
-uploaded, but not played.
-The content of effect may be modified. In particular, its field "id" is set
-to the unique id assigned by the driver. This data is required for performing
-some operations (removing an effect, controlling the playback).
-This if field must be set to -1 by the user in order to tell the driver to
-allocate a new effect.
-
-Effects are file descriptor specific.
-
-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);
-
-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
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Control of playing is done with write(). Below is an example:
-
-#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;
- stop.value = 0;
-
- write(fd, (const void*) &play, sizeof(stop));
-
-3.5 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;
-
-if (write(fd, &ie, sizeof(ie)) == -1)
- perror("set gain");
-
-3.6 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;
-
-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
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-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
-type of device, not all parameters can be dynamically updated. For example,
-the direction of an effect cannot be updated with iforce devices. In this
-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
-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-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:
-
-struct input_event {
-/* When the status of the effect changed */
- struct timeval time;
-
-/* Set to EV_FF_STATUS */
- unsigned short type;
-
-/* Contains the id of the effect */
- unsigned short code;
-
-/* Indicates the status */
- unsigned int value;
-};
-
-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
- 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.
-