1 ========================
2 Force feedback for Linux
3 ========================
4
5 :Author: Johann Deneux <johann.deneux@gmail.com
6 :Updated: Anssi Hannula <anssi.hannula@gmail.co
7
8 You may redistribute this file. Please remembe
9 interactive.svg as well.
10
11 Introduction
12 ~~~~~~~~~~~~
13
14 This document describes how to use force feedb
15 goal is not to support these devices as if the
16 (as it is already the case), but to really ena
17 effects.
18 This document only describes the force feedbac
19 interface. Please read joydev/joystick.rst and
20 this document.
21
22 Instructions to the user
23 ~~~~~~~~~~~~~~~~~~~~~~~~
24
25 To enable force feedback, you have to:
26
27 1. have your kernel configured with evdev and
28 device.
29 2. make sure evdev module is loaded and /dev/i
30 created.
31
32 Before you start, let me WARN you that some de
33 initialisation phase. This happens for example
34 To stop this annoying behaviour, move your joy
35 should keep a hand on your device, in order to
36 something goes wrong.
37
38 If you have a serial iforce device, you need t
39 joydev/joystick.rst for details.
40
41 Does it work ?
42 --------------
43
44 There is an utility called fftest that will al
45
46 % fftest /dev/input/eventXX
47
48 Instructions to the developer
49 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
50
51 All interactions are done using the event API.
52 and write() on /dev/input/eventXX.
53 This information is subject to change.
54
55 Querying device capabilities
56 ----------------------------
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)
65 unsigned long features[BITS_TO_LONGS(FF_CN
66 int ioctl(int file_descriptor, int request
67
68 "request" must be EVIOCGBIT(EV_FF, size of fea
69
70 Returns the features supported by the device.
71 following bits:
72
73 - FF_CONSTANT can render constant force effe
74 - FF_PERIODIC can render periodic effects wi
75
76 - FF_SQUARE square waveform
77 - FF_TRIANGLE triangle waveform
78 - FF_SINE sine waveform
79 - FF_SAW_UP sawtooth up waveform
80 - FF_SAW_DOWN sawtooth down waveform
81 - FF_CUSTOM custom waveform
82
83 - FF_RAMP can render ramp effects
84 - FF_SPRING can simulate the presence of a
85 - FF_FRICTION can simulate friction
86 - FF_DAMPER can simulate damper effects
87 - FF_RUMBLE rumble effects
88 - FF_INERTIA can simulate inertia
89 - FF_GAIN gain is adjustable
90 - FF_AUTOCENTER autocenter is adjustable
91
92 .. note::
93
94 - In most cases you should use FF_PERIODIC
95 devices that support FF_RUMBLE support F
96 sine) and the other way around.
97
98 - The exact syntax FF_CUSTOM is undefined
99 supports it yet.
100
101 ::
102
103 int ioctl(int fd, EVIOCGEFFECTS, int *n);
104
105 Returns the number of effects the device can k
106
107 Uploading effects to the device
108 -------------------------------
109
110 ::
111
112 #include <linux/input.h>
113 #include <sys/ioctl.h>
114
115 int ioctl(int file_descriptor, int request
116
117 "request" must be EVIOCSFF.
118
119 "effect" points to a structure describing the
120 uploaded, but not played.
121 The content of effect may be modified. In part
122 to the unique id assigned by the driver. This
123 some operations (removing an effect, controlli
124 The "id" field must be set to -1 by the user i
125 allocate a new effect.
126
127 Effects are file descriptor specific.
128
129 See <uapi/linux/input.h> for a description of
130 should also find help in a few sketches, conta
131 and interactive.svg:
132
133 .. kernel-figure:: shape.svg
134
135 Shape
136
137 .. kernel-figure:: interactive.svg
138
139 Interactive
140
141
142 Removing an effect from the device
143 ----------------------------------
144
145 ::
146
147 int ioctl(int fd, EVIOCRMFF, effect.id);
148
149 This makes room for new effects in the device'
150 stops the effect if it was playing.
151
152 Controlling the playback of effects
153 -----------------------------------
154
155 Control of playing is done with write(). Below
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(
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(
182
183 Setting the gain
184 ----------------
185
186 Not all devices have the same strength. Theref
187 factor depending on how strong they want effec
188 persistent across access to the driver.
189
190 ::
191
192 /* Set the gain of the device
193 int gain; /* between 0 and 100 *
194 struct input_event ie; /* structure u
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
203 Enabling/Disabling autocenter
204 -----------------------------
205
206 The autocenter feature quite disturbs the rend
207 and I think it should be an effect, which comp
208 type. But you can enable it if you want.
209
210 ::
211
212 int autocenter; /* between 0 a
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
222 A value of 0 means "no auto-center".
223
224 Dynamic update of an effect
225 ---------------------------
226
227 Proceed as if you wanted to upload a new effec
228 setting the id field to -1, you set it to the
229 Normally, the effect is not stopped and restar
230 type of device, not all parameters can be dyna
231 the direction of an effect cannot be updated w
232 case, the driver stops the effect, up-load it,
233
234 Therefore it is recommended to dynamically cha
235 is playing only when it is ok to restart the e
236
237 Information about the status of effects
238 ---------------------------------------
239
240 Every time the status of an effect is changed,
241 and meanings of the fields of the event are as
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 pla
258 FF_STATUS_PLAYING The effect started to
259
260 .. note::
261
262 - Status feedback is only supported by ifo
263 a really good reason to use this, please
264 linux-joystick@atrey.karlin.mff.cuni.cz
265 so that support for it can be added to t
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.