Input: update the force feedback documentation

Signed-off-by: Anssi Hannula <anssi.hannula@gmail.com>
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>

1 files changed, 52 insertions, 60 deletions

diff --git a/Documentation/input/ff.txt b/Documentation/input/ff.txt
index c7e10eaff203..c53b1c11aa40 100644
--- a/Documentation/input/ff.txt
+++ b/Documentation/input/ff.txt
@@ -1,67 +1,37 @@
 Force feedback for Linux.
 By Johann Deneux <deneux@ifrance.com> on 2001/04/22.
+Updated by 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.
 ----------------------------------------------------------------------------
 
-0. Introduction
+1. 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
 effects.
-At the moment, only I-Force devices are supported, and not officially. That
-means I had to find out how the protocol works on my own. Of course, the
-information I managed to grasp is far from being complete, and I can not
-guarranty that this driver will work for you.
-This document only describes the force feedback part of the driver for I-Force
-devices. Please read joystick.txt before reading further this document.
+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
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
-Here are instructions on how to compile and use the driver. In fact, this
-driver is the normal iforce, input and evdev drivers written by Vojtech
-Pavlik, plus additions to support force feedback.
+To enable force feedback, you have to:
+
+1. have your kernel configured with evdev and a driver that supports your
+   device.
+2. make sure evdev module is loaded and /dev/input/event* device files are
+   created.
 
 Before you start, let me WARN you that some devices shake violently during the
 initialisation phase. This happens for example with my "AVB Top Shot Pegasus".
 To stop this annoying behaviour, move you joystick to its limits. Anyway, you
-should keep a hand on your device, in order to avoid it to brake down if
+should keep a hand on your device, in order to avoid it to break down if
 something goes wrong.
 
-At the kernel's compilation:
-        - Enable IForce/Serial
-        - Enable Event interface
-
-Compile the modules, install them.
-
-You also need inputattach.
-
-You then need to insert the modules into the following order:
-% modprobe joydev
-% modprobe serport              # Only for serial
-% modprobe iforce
-% modprobe evdev
-% ./inputattach -ifor $2 &      # Only for serial
-If you are using USB, you don't need the inputattach step.
-
-Please check that you have all the /dev/input entries needed:
-cd /dev
-rm js*
-mkdir input
-mknod input/js0 c 13 0
-mknod input/js1 c 13 1
-mknod input/js2 c 13 2
-mknod input/js3 c 13 3
-ln -s input/js0 js0
-ln -s input/js1 js1
-ln -s input/js2 js2
-ln -s input/js3 js3
-
-mknod input/event0 c 13 64
-mknod input/event1 c 13 65
-mknod input/event2 c 13 66
-mknod input/event3 c 13 67
+If you have a serial iforce device, you need to start inputattach. See
+joystick.txt for details.
 
 2.1 Does it work ?
 ~~~~~~~~~~~~~~~~~~
@@ -70,9 +40,9 @@ There is an utility called fftest that will allow you to test the driver.
 
 3. Instructions to the developper
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
-  All interactions are done using the event API. That is, you can use ioctl()
+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.
+This information is subject to change.
 
 3.1 Querying device capabilities
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -86,18 +56,29 @@ int ioctl(int file_descriptor, int request, unsigned long *features);
 
 Returns the features supported by the device. features is a bitfield with the
 following bits:
-- FF_X          has an X axis (usually joysticks)
-- FF_Y          has an Y axis (usually joysticks)
-- FF_WHEEL      has a wheel (usually sterring wheels)
 - FF_CONSTANT   can render constant force effects
-- FF_PERIODIC   can render periodic effects (sine, triangle, square...)
+- 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 
+- FF_FRICTION   can simulate friction
 - FF_DAMPER     can simulate damper effects
-- FF_RUMBLE     rumble effects (normally the only effect supported by rumble
-                pads)
+- FF_RUMBLE     rumble effects
 - FF_INERTIA    can simulate inertia
+- FF_GAIN       gain is adjustable
+- FF_AUTOCENTER autocenter is adjustable
+
+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
+      supports it yet.
 
 
 int ioctl(int fd, EVIOCGEFFECTS, int *n);
@@ -108,7 +89,7 @@ Returns the number of effects the device can keep in its memory.
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 #include <linux/input.h>
 #include <sys/ioctl.h>
- 
+
 int ioctl(int file_descriptor, int request, struct ff_effect *effect);
 
 "request" must be EVIOCSFF.
@@ -120,6 +101,9 @@ to the unique id assigned by the driver. This data is required for performing
 some operations (removing an effect, controlling the playback).
 This if field must be set to -1 by the user in order to tell the driver to
 allocate a new effect.
+
+Effects are file descriptor specific.
+
 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.
@@ -128,8 +112,8 @@ You need xfig to visualize these files.
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 int ioctl(int fd, EVIOCRMFF, effect.id);
 
-This makes room for new effects in the device's memory. Please note this won't
-stop the effect if it was playing.
+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
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
@@ -149,22 +133,21 @@ Control of playing is done with write(). Below is an example:
         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;
         stop.value = 0;
-        
+
         write(fd, (const void*) &play, sizeof(stop));
 
 3.5 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, so you should not care about it if
-you are writing games, as another utility probably already set this for you.
+persistent across access to the driver.
 
 /* Set the gain of the device
 int gain;               /* between 0 and 100 */
@@ -204,11 +187,14 @@ type of device, not all parameters can be dynamically updated. For example,
 the direction of an effect cannot be updated with iforce devices. In this
 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
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 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:
+
 struct input_event {
 /* When the status of the effect changed */
         struct timeval time;
@@ -225,3 +211,9 @@ struct input_event {
 
 FF_STATUS_STOPPED       The effect stopped playing
 FF_STATUS_PLAYING       The effect started to play
+
+NOTE: 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.
+