diff options
| -rw-r--r-- | Documentation/input/ff.txt | 188 |
1 files changed, 112 insertions, 76 deletions
diff --git a/Documentation/input/ff.txt b/Documentation/input/ff.txt index b3867bf49f8f..6d6688a63dd8 100644 --- a/Documentation/input/ff.txt +++ b/Documentation/input/ff.txt @@ -1,12 +1,16 @@ -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. +======================== +Force feedback for Linux +======================== + +:Author: Johann Deneux <johann.deneux@gmail.com> on 2001/04/22. +:Updated: 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 -~~~~~~~~~~~~~~~ +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 @@ -15,8 +19,9 @@ 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 -~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Instructions to the user +~~~~~~~~~~~~~~~~~~~~~~~~ + To enable force feedback, you have to: 1. have your kernel configured with evdev and a driver that supports your @@ -33,39 +38,48 @@ 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 +Does it work ? +-------------- + +There is an utility called fftest that will allow you to test the driver:: + + % fftest /dev/input/eventXX + +Instructions to the developer +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -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> +Querying device capabilities +---------------------------- -#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); +:: + + #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 @@ -75,24 +89,30 @@ following bits: - FF_GAIN gain is adjustable - FF_AUTOCENTER autocenter is adjustable -Note: In most cases you should use FF_PERIODIC instead of FF_RUMBLE. All +.. 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 + - The exact syntax FF_CUSTOM is undefined for the time being as no driver supports it yet. +:: -int ioctl(int fd, EVIOCGEFFECTS, int *n); + 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> +Uploading effects to the device +------------------------------- + +:: -int ioctl(int file_descriptor, int request, struct ff_effect *effect); + #include <linux/input.h> + #include <sys/ioctl.h> + + int ioctl(int file_descriptor, int request, struct ff_effect *effect); "request" must be EVIOCSFF. @@ -110,34 +130,41 @@ 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); + +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 -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Controlling the playback of effects +----------------------------------- + Control of playing is done with write(). Below is an example: -#include <linux/input.h> -#include <unistd.h> +:: + + #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; @@ -145,43 +172,50 @@ Control of playing is done with write(). Below is an example: write(fd, (const void*) &play, sizeof(stop)); -3.5 Setting the gain -~~~~~~~~~~~~~~~~~~~~ +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; + /* Set the gain of the device + int gain; /* between 0 and 100 */ + struct input_event ie; /* structure used to communicate with the driver */ -if (write(fd, &ie, sizeof(ie)) == -1) + 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 -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +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; + int autocenter; /* between 0 and 100 */ + struct input_event ie; -if (write(fd, &ie, sizeof(ie)) == -1) + 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 -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +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 @@ -192,30 +226,32 @@ 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 -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +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: +and meanings of the fields of the event are as follows:: + + struct input_event { + /* When the status of the effect changed */ + struct timeval time; -struct input_event { -/* When the status of the effect changed */ - struct timeval time; + /* Set to EV_FF_STATUS */ + unsigned short type; -/* Set to EV_FF_STATUS */ - unsigned short type; + /* Contains the id of the effect */ + unsigned short code; -/* Contains the id of the effect */ - unsigned short code; + /* Indicates the status */ + unsigned int value; + }; -/* Indicates the status */ - unsigned int value; -}; + FF_STATUS_STOPPED The effect stopped playing + FF_STATUS_PLAYING The effect started to play -FF_STATUS_STOPPED The effect stopped playing -FF_STATUS_PLAYING The effect started to play +.. note:: -NOTE: Status feedback is only supported by iforce driver. If you have + - 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. - |