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1========================2Force feedback for Linux3========================4 5:Author: Johann Deneux <johann.deneux@gmail.com> on 2001/04/22.6:Updated: Anssi Hannula <anssi.hannula@gmail.com> on 2006/04/09.7 8You may redistribute this file. Please remember to include shape.svg and9interactive.svg as well.10 11Introduction12~~~~~~~~~~~~13 14This document describes how to use force feedback devices under Linux. The15goal is not to support these devices as if they were simple input-only devices16(as it is already the case), but to really enable the rendering of force17effects.18This document only describes the force feedback part of the Linux input19interface. Please read joydev/joystick.rst and input.rst before reading further20this document.21 22Instructions to the user23~~~~~~~~~~~~~~~~~~~~~~~~24 25To enable force feedback, you have to:26 271. have your kernel configured with evdev and a driver that supports your28 device.292. make sure evdev module is loaded and /dev/input/event* device files are30 created.31 32Before you start, let me WARN you that some devices shake violently during the33initialisation phase. This happens for example with my "AVB Top Shot Pegasus".34To stop this annoying behaviour, move your joystick to its limits. Anyway, you35should keep a hand on your device, in order to avoid it to break down if36something goes wrong.37 38If you have a serial iforce device, you need to start inputattach. See39joydev/joystick.rst for details.40 41Does it work ?42--------------43 44There is an utility called fftest that will allow you to test the driver::45 46 % fftest /dev/input/eventXX47 48Instructions to the developer49~~~~~~~~~~~~~~~~~~~~~~~~~~~~~50 51All interactions are done using the event API. That is, you can use ioctl()52and write() on /dev/input/eventXX.53This information is subject to change.54 55Querying device capabilities56----------------------------57 58::59 60 #include <linux/input.h>61 #include <sys/ioctl.h>62 63 #define BITS_TO_LONGS(x) \64 (((x) + 8 * sizeof (unsigned long) - 1) / (8 * sizeof (unsigned long)))65 unsigned long features[BITS_TO_LONGS(FF_CNT)];66 int ioctl(int file_descriptor, int request, unsigned long *features);67 68"request" must be EVIOCGBIT(EV_FF, size of features array in bytes )69 70Returns the features supported by the device. features is a bitfield with the71following bits:72 73- FF_CONSTANT can render constant force effects74- FF_PERIODIC can render periodic effects with the following waveforms:75 76 - FF_SQUARE square waveform77 - FF_TRIANGLE triangle waveform78 - FF_SINE sine waveform79 - FF_SAW_UP sawtooth up waveform80 - FF_SAW_DOWN sawtooth down waveform81 - FF_CUSTOM custom waveform82 83- FF_RAMP can render ramp effects84- FF_SPRING can simulate the presence of a spring85- FF_FRICTION can simulate friction86- FF_DAMPER can simulate damper effects87- FF_RUMBLE rumble effects88- FF_INERTIA can simulate inertia89- FF_GAIN gain is adjustable90- FF_AUTOCENTER autocenter is adjustable91 92.. note::93 94 - In most cases you should use FF_PERIODIC instead of FF_RUMBLE. All95 devices that support FF_RUMBLE support FF_PERIODIC (square, triangle,96 sine) and the other way around.97 98 - The exact syntax FF_CUSTOM is undefined for the time being as no driver99 supports it yet.100 101::102 103 int ioctl(int fd, EVIOCGEFFECTS, int *n);104 105Returns the number of effects the device can keep in its memory.106 107Uploading effects to the device108-------------------------------109 110::111 112 #include <linux/input.h>113 #include <sys/ioctl.h>114 115 int ioctl(int file_descriptor, int request, struct ff_effect *effect);116 117"request" must be EVIOCSFF.118 119"effect" points to a structure describing the effect to upload. The effect is120uploaded, but not played.121The content of effect may be modified. In particular, its field "id" is set122to the unique id assigned by the driver. This data is required for performing123some operations (removing an effect, controlling the playback).124The "id" field must be set to -1 by the user in order to tell the driver to125allocate a new effect.126 127Effects are file descriptor specific.128 129See <uapi/linux/input.h> for a description of the ff_effect struct. You130should also find help in a few sketches, contained in files shape.svg131and interactive.svg:132 133.. kernel-figure:: shape.svg134 135 Shape136 137.. kernel-figure:: interactive.svg138 139 Interactive140 141 142Removing an effect from the device143----------------------------------144 145::146 147 int ioctl(int fd, EVIOCRMFF, effect.id);148 149This makes room for new effects in the device's memory. Note that this also150stops the effect if it was playing.151 152Controlling the playback of effects153-----------------------------------154 155Control of playing is done with write(). Below is an example:156 157::158 159 #include <linux/input.h>160 #include <unistd.h>161 162 struct input_event play;163 struct input_event stop;164 struct ff_effect effect;165 int fd;166 ...167 fd = open("/dev/input/eventXX", O_RDWR);168 ...169 /* Play three times */170 play.type = EV_FF;171 play.code = effect.id;172 play.value = 3;173 174 write(fd, (const void*) &play, sizeof(play));175 ...176 /* Stop an effect */177 stop.type = EV_FF;178 stop.code = effect.id;179 stop.value = 0;180 181 write(fd, (const void*) &stop, sizeof(stop));182 183Setting the gain184----------------185 186Not all devices have the same strength. Therefore, users should set a gain187factor depending on how strong they want effects to be. This setting is188persistent across access to the driver.189 190::191 192 /* Set the gain of the device193 int gain; /* between 0 and 100 */194 struct input_event ie; /* structure used to communicate with the driver */195 196 ie.type = EV_FF;197 ie.code = FF_GAIN;198 ie.value = 0xFFFFUL * gain / 100;199 200 if (write(fd, &ie, sizeof(ie)) == -1)201 perror("set gain");202 203Enabling/Disabling autocenter204-----------------------------205 206The autocenter feature quite disturbs the rendering of effects in my opinion,207and I think it should be an effect, which computation depends on the game208type. But you can enable it if you want.209 210::211 212 int autocenter; /* between 0 and 100 */213 struct input_event ie;214 215 ie.type = EV_FF;216 ie.code = FF_AUTOCENTER;217 ie.value = 0xFFFFUL * autocenter / 100;218 219 if (write(fd, &ie, sizeof(ie)) == -1)220 perror("set auto-center");221 222A value of 0 means "no auto-center".223 224Dynamic update of an effect225---------------------------226 227Proceed as if you wanted to upload a new effect, except that instead of228setting the id field to -1, you set it to the wanted effect id.229Normally, the effect is not stopped and restarted. However, depending on the230type of device, not all parameters can be dynamically updated. For example,231the direction of an effect cannot be updated with iforce devices. In this232case, the driver stops the effect, up-load it, and restart it.233 234Therefore it is recommended to dynamically change direction while the effect235is playing only when it is ok to restart the effect with a replay count of 1.236 237Information about the status of effects238---------------------------------------239 240Every time the status of an effect is changed, an event is sent. The values241and meanings of the fields of the event are as follows::242 243 struct input_event {244 /* When the status of the effect changed */245 struct timeval time;246 247 /* Set to EV_FF_STATUS */248 unsigned short type;249 250 /* Contains the id of the effect */251 unsigned short code;252 253 /* Indicates the status */254 unsigned int value;255 };256 257 FF_STATUS_STOPPED The effect stopped playing258 FF_STATUS_PLAYING The effect started to play259 260.. note::261 262 - Status feedback is only supported by iforce driver. If you have263 a really good reason to use this, please contact264 linux-joystick@atrey.karlin.mff.cuni.cz or anssi.hannula@gmail.com265 so that support for it can be added to the rest of the drivers.266