1Force feedback for Linux. 2By Johann Deneux <deneux@ifrance.com> on 2001/04/22. 3 4---------------------------------------------------------------------------- 5 60. Introduction 7~~~~~~~~~~~~~~~ 8This document describes how to use force feedback devices under Linux. The 9goal is not to support these devices as if they were simple input-only devices 10(as it is already the case), but to really enable the rendering of force 11effects. 12At the moment, only I-Force devices are supported, and not officially. That 13means I had to find out how the protocol works on my own. Of course, the 14information I managed to grasp is far from being complete, and I can not 15guarranty that this driver will work for you. 16This document only describes the force feedback part of the driver for I-Force 17devices. Please read joystick.txt before reading further this document. 18 192. Instructions to the user 20~~~~~~~~~~~~~~~~~~~~~~~~~~~ 21Here are instructions on how to compile and use the driver. In fact, this 22driver is the normal iforce.o, input.o and evdev.o drivers written by Vojtech 23Pavlik, plus additions to support force feedback. 24 25Before you start, let me WARN you that some devices shake violently during the 26initialisation phase. This happens for example with my "AVB Top Shot Pegasus". 27To stop this annoying behaviour, move you joystick to its limits. Anyway, you 28should keep a hand on your device, in order to avoid it to brake down if 29something goes wrong. 30 31At the kernel's compilation: 32 - Enable IForce/Serial 33 - Enable Event interface 34 35Compile the modules, install them. 36 37You also need inputattach. 38 39You then need to insert the modules into the following order: 40% modprobe joydev 41% modprobe serport 42% modprobe iforce 43% modprobe evdev 44% ./inputattach -ifor $2 & # Only for serial 45For convenience, you may use the shell script named "ff" available from 46the cvs tree of the Linux Console Project at sourceforge. You can also 47retrieve it from http://www.esil.univ-mrs.fr/~jdeneux/projects/ff/. 48If you are using USB, you don't need the inputattach step. 49 50Please check that you have all the /dev/input entries needed: 51cd /dev 52rm js* 53mkdir input 54mknod input/js0 c 13 0 55mknod input/js1 c 13 1 56mknod input/js2 c 13 2 57mknod input/js3 c 13 3 58ln -s input/js0 js0 59ln -s input/js1 js1 60ln -s input/js2 js2 61ln -s input/js3 js3 62 63mknod input/event0 c 13 64 64mknod input/event1 c 13 65 65mknod input/event2 c 13 66 66mknod input/event3 c 13 67 67 682.1 Does it work ? 69~~~~~~~~~~~~~~~~~~ 70There is an utility called fftest that will allow you to test the driver. 71% fftest /dev/eventXX 72 733. Instructions to the developper 74~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 75 All interactions are done using the event API. That is, you can use ioctl() 76and write() on /dev/input/eventXX. 77 This information is subject to change. 78 793.1 Querying device capabilities 80~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 81#include <linux/input.h> 82#include <sys/ioctl.h> 83 84int ioctl(int file_descriptor, int request, unsigned long *features); 85 86"request" must be EVIOCGBIT(EV_FF, sizeof(unsigned long)) 87 88Returns the features supported by the device. features is a bitfield with the 89following bits: 90- FF_X has an X axis (should allways be the case) 91- FF_Y has an Y axis (usually not the case for wheels) 92- FF_CONSTANT can render constant force effects 93- FF_PERIODIC can render periodic effects (sine, ramp, square...) 94- FF_SPRING can simulate the presence of a spring 95- FF_FRICTION can simulate friction (aka drag, damper effect...) 96- FF_RUMBLE rumble effects (normally the only effect supported by rumble 97 pads) 98- 8 bits from FF_N_EFFECTS_0 containing the number of effects that can be 99 simultaneously played. 100 1013.2 Uploading effects to the device 102~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 103#include <linux/input.h> 104#include <sys/ioctl.h> 105 106int ioctl(int file_descriptor, int request, struct ff_effect *effect); 107 108"request" must be EVIOCSFF. 109 110"effect" points to a structure describing the effect to upload. The effect is 111uploaded, but not played. 112The content of effect may be modified. In particular, its field "id" is set 113to the unique id assigned by the driver. This data is required for performing 114some operations (removing an effect, controlling the playback). 115See <linux/input.h> for a description of the ff_effect stuct. 116 1173.3 Removing an effect from the device 118~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 119int ioctl(int fd, EVIOCRMFF, effect.id); 120 121This makes room for new effects in the device's memory. Please note this won't 122stop the effect if it was playing. 123 1243.4 Controlling the playback of effects 125~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 126Control of playing is done with write(). Below is an example: 127 128#include <linux/input.h> 129#include <unistd.h> 130 131 struct input_event play; 132 struct input_event stop; 133 struct ff_effect effect; 134 int fd; 135... 136 fd = open("/dev/input/eventXX", O_RDWR); 137... 138 /* Play three times */ 139 play.type = EV_FF; 140 play.code = effect.id; 141 play.value = 3; 142 143 write(fd, (const void*) &play, sizeof(play)); 144... 145 /* Stop an effect */ 146 stop.type = EV_FF; 147 stop.code = effect.id; 148 stop.value = 0; 149 150 write(fd, (const void*) &play, sizeof(stop)); 151 1523.5 Setting the gain 153~~~~~~~~~~~~~~~~~~~~ 154Not all devices have the same strength. Therefore, users should set a gain 155factor depending on how strong they want effects to be. This setting is 156persistent accross access to the driver, so you should not care about it if 157you are writing games, as another utility probably already set this for you. 158 159/* Set the gain of the device 160int gain; /* between 0 and 100 */ 161struct input_event ie; /* structure used to communicate with the driver */ 162 163ie.type = EV_FF; 164ie.code = FF_GAIN; 165ie.value = 0xFFFFUL * gain / 100; 166 167if (write(fd, &ie, sizeof(ie)) == -1) 168 perror("set gain"); 169 1703.6 Enabling/Disabling autocenter 171~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 172The autocenter feature quite disturbs the rendering of effects in my opinion, 173and I think it should be an effect, which computation depends on the game 174type. But you can enable it if you want. 175 176int autocenter; /* between 0 and 100 */ 177struct input_event ie; 178 179ie.type = EV_FF; 180ie.code = FF_AUTOCENTER; 181ie.value = 0xFFFFUL * autocenter / 100; 182 183if (write(fd, &ie, sizeof(ie)) == -1) 184 perror("set auto-center"); 185 186A value of 0 means "no auto-center". 187 1883.7 Dynamic update of an effect 189~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 190This consists in changing some parameters of an effect while it's playing. The 191driver currently does not support that. You still have the brute-force method, 192which consists in erasing the effect and uploading the updated version. It 193actually works pretty well. You don't need to stop-and-start the effect. 194 195