1 ======================== 1 ========================
2 Force feedback for Linux 2 Force feedback for Linux
3 ======================== 3 ========================
4 4
5 :Author: Johann Deneux <johann.deneux@gmail.com 5 :Author: Johann Deneux <johann.deneux@gmail.com> on 2001/04/22.
6 :Updated: Anssi Hannula <anssi.hannula@gmail.co 6 :Updated: Anssi Hannula <anssi.hannula@gmail.com> on 2006/04/09.
7 7
8 You may redistribute this file. Please remembe 8 You may redistribute this file. Please remember to include shape.svg and
9 interactive.svg as well. 9 interactive.svg as well.
10 10
11 Introduction 11 Introduction
12 ~~~~~~~~~~~~ 12 ~~~~~~~~~~~~
13 13
14 This document describes how to use force feedb 14 This document describes how to use force feedback devices under Linux. The
15 goal is not to support these devices as if the 15 goal is not to support these devices as if they were simple input-only devices
16 (as it is already the case), but to really ena 16 (as it is already the case), but to really enable the rendering of force
17 effects. 17 effects.
18 This document only describes the force feedbac 18 This document only describes the force feedback part of the Linux input
19 interface. Please read joydev/joystick.rst and !! 19 interface. Please read joystick.txt and input.txt before reading further this
20 this document. !! 20 document.
21 21
22 Instructions to the user 22 Instructions to the user
23 ~~~~~~~~~~~~~~~~~~~~~~~~ 23 ~~~~~~~~~~~~~~~~~~~~~~~~
24 24
25 To enable force feedback, you have to: 25 To enable force feedback, you have to:
26 26
27 1. have your kernel configured with evdev and 27 1. have your kernel configured with evdev and a driver that supports your
28 device. 28 device.
29 2. make sure evdev module is loaded and /dev/i 29 2. make sure evdev module is loaded and /dev/input/event* device files are
30 created. 30 created.
31 31
32 Before you start, let me WARN you that some de 32 Before you start, let me WARN you that some devices shake violently during the
33 initialisation phase. This happens for example 33 initialisation phase. This happens for example with my "AVB Top Shot Pegasus".
34 To stop this annoying behaviour, move your joy 34 To stop this annoying behaviour, move your joystick to its limits. Anyway, you
35 should keep a hand on your device, in order to 35 should keep a hand on your device, in order to avoid it to break down if
36 something goes wrong. 36 something goes wrong.
37 37
38 If you have a serial iforce device, you need t 38 If you have a serial iforce device, you need to start inputattach. See
39 joydev/joystick.rst for details. !! 39 joystick.txt for details.
40 40
41 Does it work ? 41 Does it work ?
42 -------------- 42 --------------
43 43
44 There is an utility called fftest that will al 44 There is an utility called fftest that will allow you to test the driver::
45 45
46 % fftest /dev/input/eventXX 46 % fftest /dev/input/eventXX
47 47
48 Instructions to the developer 48 Instructions to the developer
49 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 49 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
50 50
51 All interactions are done using the event API. 51 All interactions are done using the event API. That is, you can use ioctl()
52 and write() on /dev/input/eventXX. 52 and write() on /dev/input/eventXX.
53 This information is subject to change. 53 This information is subject to change.
54 54
55 Querying device capabilities 55 Querying device capabilities
56 ---------------------------- 56 ----------------------------
57 57
58 :: 58 ::
59 59
60 #include <linux/input.h> 60 #include <linux/input.h>
61 #include <sys/ioctl.h> 61 #include <sys/ioctl.h>
62 62
63 #define BITS_TO_LONGS(x) \ 63 #define BITS_TO_LONGS(x) \
64 (((x) + 8 * sizeof (unsigned long) 64 (((x) + 8 * sizeof (unsigned long) - 1) / (8 * sizeof (unsigned long)))
65 unsigned long features[BITS_TO_LONGS(FF_CN 65 unsigned long features[BITS_TO_LONGS(FF_CNT)];
66 int ioctl(int file_descriptor, int request 66 int ioctl(int file_descriptor, int request, unsigned long *features);
67 67
68 "request" must be EVIOCGBIT(EV_FF, size of fea 68 "request" must be EVIOCGBIT(EV_FF, size of features array in bytes )
69 69
70 Returns the features supported by the device. 70 Returns the features supported by the device. features is a bitfield with the
71 following bits: 71 following bits:
72 72
73 - FF_CONSTANT can render constant force effe 73 - FF_CONSTANT can render constant force effects
74 - FF_PERIODIC can render periodic effects wi 74 - FF_PERIODIC can render periodic effects with the following waveforms:
75 75
76 - FF_SQUARE square waveform 76 - FF_SQUARE square waveform
77 - FF_TRIANGLE triangle waveform 77 - FF_TRIANGLE triangle waveform
78 - FF_SINE sine waveform 78 - FF_SINE sine waveform
79 - FF_SAW_UP sawtooth up waveform 79 - FF_SAW_UP sawtooth up waveform
80 - FF_SAW_DOWN sawtooth down waveform 80 - FF_SAW_DOWN sawtooth down waveform
81 - FF_CUSTOM custom waveform 81 - FF_CUSTOM custom waveform
82 82
83 - FF_RAMP can render ramp effects 83 - FF_RAMP can render ramp effects
84 - FF_SPRING can simulate the presence of a 84 - FF_SPRING can simulate the presence of a spring
85 - FF_FRICTION can simulate friction 85 - FF_FRICTION can simulate friction
86 - FF_DAMPER can simulate damper effects 86 - FF_DAMPER can simulate damper effects
87 - FF_RUMBLE rumble effects 87 - FF_RUMBLE rumble effects
88 - FF_INERTIA can simulate inertia 88 - FF_INERTIA can simulate inertia
89 - FF_GAIN gain is adjustable 89 - FF_GAIN gain is adjustable
90 - FF_AUTOCENTER autocenter is adjustable 90 - FF_AUTOCENTER autocenter is adjustable
91 91
92 .. note:: 92 .. note::
93 93
94 - In most cases you should use FF_PERIODIC 94 - In most cases you should use FF_PERIODIC instead of FF_RUMBLE. All
95 devices that support FF_RUMBLE support F 95 devices that support FF_RUMBLE support FF_PERIODIC (square, triangle,
96 sine) and the other way around. 96 sine) and the other way around.
97 97
98 - The exact syntax FF_CUSTOM is undefined 98 - The exact syntax FF_CUSTOM is undefined for the time being as no driver
99 supports it yet. 99 supports it yet.
100 100
101 :: 101 ::
102 102
103 int ioctl(int fd, EVIOCGEFFECTS, int *n); 103 int ioctl(int fd, EVIOCGEFFECTS, int *n);
104 104
105 Returns the number of effects the device can k 105 Returns the number of effects the device can keep in its memory.
106 106
107 Uploading effects to the device 107 Uploading effects to the device
108 ------------------------------- 108 -------------------------------
109 109
110 :: 110 ::
111 111
112 #include <linux/input.h> 112 #include <linux/input.h>
113 #include <sys/ioctl.h> 113 #include <sys/ioctl.h>
114 114
115 int ioctl(int file_descriptor, int request 115 int ioctl(int file_descriptor, int request, struct ff_effect *effect);
116 116
117 "request" must be EVIOCSFF. 117 "request" must be EVIOCSFF.
118 118
119 "effect" points to a structure describing the 119 "effect" points to a structure describing the effect to upload. The effect is
120 uploaded, but not played. 120 uploaded, but not played.
121 The content of effect may be modified. In part 121 The content of effect may be modified. In particular, its field "id" is set
122 to the unique id assigned by the driver. This 122 to the unique id assigned by the driver. This data is required for performing
123 some operations (removing an effect, controlli 123 some operations (removing an effect, controlling the playback).
124 The "id" field must be set to -1 by the user i 124 The "id" field must be set to -1 by the user in order to tell the driver to
125 allocate a new effect. 125 allocate a new effect.
126 126
127 Effects are file descriptor specific. 127 Effects are file descriptor specific.
128 128
129 See <uapi/linux/input.h> for a description of 129 See <uapi/linux/input.h> for a description of the ff_effect struct. You
130 should also find help in a few sketches, conta 130 should also find help in a few sketches, contained in files shape.svg
131 and interactive.svg: 131 and interactive.svg:
132 132
133 .. kernel-figure:: shape.svg 133 .. kernel-figure:: shape.svg
134 134
135 Shape 135 Shape
136 136
137 .. kernel-figure:: interactive.svg 137 .. kernel-figure:: interactive.svg
138 138
139 Interactive 139 Interactive
140 140
141 141
142 Removing an effect from the device 142 Removing an effect from the device
143 ---------------------------------- 143 ----------------------------------
144 144
145 :: 145 ::
146 146
147 int ioctl(int fd, EVIOCRMFF, effect.id); 147 int ioctl(int fd, EVIOCRMFF, effect.id);
148 148
149 This makes room for new effects in the device' 149 This makes room for new effects in the device's memory. Note that this also
150 stops the effect if it was playing. 150 stops the effect if it was playing.
151 151
152 Controlling the playback of effects 152 Controlling the playback of effects
153 ----------------------------------- 153 -----------------------------------
154 154
155 Control of playing is done with write(). Below 155 Control of playing is done with write(). Below is an example:
156 156
157 :: 157 ::
158 158
159 #include <linux/input.h> 159 #include <linux/input.h>
160 #include <unistd.h> 160 #include <unistd.h>
161 161
162 struct input_event play; 162 struct input_event play;
163 struct input_event stop; 163 struct input_event stop;
164 struct ff_effect effect; 164 struct ff_effect effect;
165 int fd; 165 int fd;
166 ... 166 ...
167 fd = open("/dev/input/eventXX", O_RDWR 167 fd = open("/dev/input/eventXX", O_RDWR);
168 ... 168 ...
169 /* Play three times */ 169 /* Play three times */
170 play.type = EV_FF; 170 play.type = EV_FF;
171 play.code = effect.id; 171 play.code = effect.id;
172 play.value = 3; 172 play.value = 3;
173 173
174 write(fd, (const void*) &play, sizeof( 174 write(fd, (const void*) &play, sizeof(play));
175 ... 175 ...
176 /* Stop an effect */ 176 /* Stop an effect */
177 stop.type = EV_FF; 177 stop.type = EV_FF;
178 stop.code = effect.id; 178 stop.code = effect.id;
179 stop.value = 0; 179 stop.value = 0;
180 180
181 write(fd, (const void*) &stop, sizeof( 181 write(fd, (const void*) &stop, sizeof(stop));
182 182
183 Setting the gain 183 Setting the gain
184 ---------------- 184 ----------------
185 185
186 Not all devices have the same strength. Theref 186 Not all devices have the same strength. Therefore, users should set a gain
187 factor depending on how strong they want effec 187 factor depending on how strong they want effects to be. This setting is
188 persistent across access to the driver. 188 persistent across access to the driver.
189 189
190 :: 190 ::
191 191
192 /* Set the gain of the device 192 /* Set the gain of the device
193 int gain; /* between 0 and 100 * 193 int gain; /* between 0 and 100 */
194 struct input_event ie; /* structure u 194 struct input_event ie; /* structure used to communicate with the driver */
195 195
196 ie.type = EV_FF; 196 ie.type = EV_FF;
197 ie.code = FF_GAIN; 197 ie.code = FF_GAIN;
198 ie.value = 0xFFFFUL * gain / 100; 198 ie.value = 0xFFFFUL * gain / 100;
199 199
200 if (write(fd, &ie, sizeof(ie)) == -1) 200 if (write(fd, &ie, sizeof(ie)) == -1)
201 perror("set gain"); 201 perror("set gain");
202 202
203 Enabling/Disabling autocenter 203 Enabling/Disabling autocenter
204 ----------------------------- 204 -----------------------------
205 205
206 The autocenter feature quite disturbs the rend 206 The autocenter feature quite disturbs the rendering of effects in my opinion,
207 and I think it should be an effect, which comp 207 and I think it should be an effect, which computation depends on the game
208 type. But you can enable it if you want. 208 type. But you can enable it if you want.
209 209
210 :: 210 ::
211 211
212 int autocenter; /* between 0 a 212 int autocenter; /* between 0 and 100 */
213 struct input_event ie; 213 struct input_event ie;
214 214
215 ie.type = EV_FF; 215 ie.type = EV_FF;
216 ie.code = FF_AUTOCENTER; 216 ie.code = FF_AUTOCENTER;
217 ie.value = 0xFFFFUL * autocenter / 100; 217 ie.value = 0xFFFFUL * autocenter / 100;
218 218
219 if (write(fd, &ie, sizeof(ie)) == -1) 219 if (write(fd, &ie, sizeof(ie)) == -1)
220 perror("set auto-center"); 220 perror("set auto-center");
221 221
222 A value of 0 means "no auto-center". 222 A value of 0 means "no auto-center".
223 223
224 Dynamic update of an effect 224 Dynamic update of an effect
225 --------------------------- 225 ---------------------------
226 226
227 Proceed as if you wanted to upload a new effec 227 Proceed as if you wanted to upload a new effect, except that instead of
228 setting the id field to -1, you set it to the 228 setting the id field to -1, you set it to the wanted effect id.
229 Normally, the effect is not stopped and restar 229 Normally, the effect is not stopped and restarted. However, depending on the
230 type of device, not all parameters can be dyna 230 type of device, not all parameters can be dynamically updated. For example,
231 the direction of an effect cannot be updated w 231 the direction of an effect cannot be updated with iforce devices. In this
232 case, the driver stops the effect, up-load it, 232 case, the driver stops the effect, up-load it, and restart it.
233 233
234 Therefore it is recommended to dynamically cha 234 Therefore it is recommended to dynamically change direction while the effect
235 is playing only when it is ok to restart the e 235 is playing only when it is ok to restart the effect with a replay count of 1.
236 236
237 Information about the status of effects 237 Information about the status of effects
238 --------------------------------------- 238 ---------------------------------------
239 239
240 Every time the status of an effect is changed, 240 Every time the status of an effect is changed, an event is sent. The values
241 and meanings of the fields of the event are as 241 and meanings of the fields of the event are as follows::
242 242
243 struct input_event { 243 struct input_event {
244 /* When the status of the effect changed * 244 /* When the status of the effect changed */
245 struct timeval time; 245 struct timeval time;
246 246
247 /* Set to EV_FF_STATUS */ 247 /* Set to EV_FF_STATUS */
248 unsigned short type; 248 unsigned short type;
249 249
250 /* Contains the id of the effect */ 250 /* Contains the id of the effect */
251 unsigned short code; 251 unsigned short code;
252 252
253 /* Indicates the status */ 253 /* Indicates the status */
254 unsigned int value; 254 unsigned int value;
255 }; 255 };
256 256
257 FF_STATUS_STOPPED The effect stopped pla 257 FF_STATUS_STOPPED The effect stopped playing
258 FF_STATUS_PLAYING The effect started to 258 FF_STATUS_PLAYING The effect started to play
259 259
260 .. note:: 260 .. note::
261 261
262 - Status feedback is only supported by ifo 262 - Status feedback is only supported by iforce driver. If you have
263 a really good reason to use this, please 263 a really good reason to use this, please contact
264 linux-joystick@atrey.karlin.mff.cuni.cz 264 linux-joystick@atrey.karlin.mff.cuni.cz or anssi.hannula@gmail.com
265 so that support for it can be added to t 265 so that support for it can be added to the rest of the drivers.
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