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+===============
+Iforce Protocol
+===============
+
+:Author: Johann Deneux <johann.deneux@gmail.com>
+
+Home page at `<http://web.archive.org/web/*/http://www.esil.univ-mrs.fr>`_
+
+:Additions: by Vojtech Pavlik.
+
+
+Introduction
+============
+
+This document describes what I managed to discover about the protocol used to
+specify force effects to I-Force 2.0 devices. None of this information comes
+from Immerse. That's why you should not trust what is written in this
+document. This document is intended to help understanding the protocol.
+This is not a reference. Comments and corrections are welcome. To contact me,
+send an email to: johann.deneux@gmail.com
+
+.. warning::
+
+ I shall not be held responsible for any damage or harm caused if you try to
+ send data to your I-Force device based on what you read in this document.
+
+Preliminary Notes
+=================
+
+All values are hexadecimal with big-endian encoding (msb on the left). Beware,
+values inside packets are encoded using little-endian. Bytes whose roles are
+unknown are marked ??? Information that needs deeper inspection is marked (?)
+
+General form of a packet
+------------------------
+
+This is how packets look when the device uses the rs232 to communicate.
+
+== == === ==== ==
+2B OP LEN DATA CS
+== == === ==== ==
+
+CS is the checksum. It is equal to the exclusive or of all bytes.
+
+When using USB:
+
+== ====
+OP DATA
+== ====
+
+The 2B, LEN and CS fields have disappeared, probably because USB handles
+frames and data corruption is handled or unsignificant.
+
+First, I describe effects that are sent by the device to the computer
+
+Device input state
+==================
+
+This packet is used to indicate the state of each button and the value of each
+axis::
+
+ OP= 01 for a joystick, 03 for a wheel
+ LEN= Varies from device to device
+ 00 X-Axis lsb
+ 01 X-Axis msb
+ 02 Y-Axis lsb, or gas pedal for a wheel
+ 03 Y-Axis msb, or brake pedal for a wheel
+ 04 Throttle
+ 05 Buttons
+ 06 Lower 4 bits: Buttons
+ Upper 4 bits: Hat
+ 07 Rudder
+
+Device effects states
+=====================
+
+::
+
+ OP= 02
+ LEN= Varies
+ 00 ? Bit 1 (Value 2) is the value of the deadman switch
+ 01 Bit 8 is set if the effect is playing. Bits 0 to 7 are the effect id.
+ 02 ??
+ 03 Address of parameter block changed (lsb)
+ 04 Address of parameter block changed (msb)
+ 05 Address of second parameter block changed (lsb)
+ ... depending on the number of parameter blocks updated
+
+Force effect
+------------
+
+::
+
+ OP= 01
+ LEN= 0e
+ 00 Channel (when playing several effects at the same time, each must
+ be assigned a channel)
+ 01 Wave form
+ Val 00 Constant
+ Val 20 Square
+ Val 21 Triangle
+ Val 22 Sine
+ Val 23 Sawtooth up
+ Val 24 Sawtooth down
+ Val 40 Spring (Force = f(pos))
+ Val 41 Friction (Force = f(velocity)) and Inertia
+ (Force = f(acceleration))
+
+
+ 02 Axes affected and trigger
+ Bits 4-7: Val 2 = effect along one axis. Byte 05 indicates direction
+ Val 4 = X axis only. Byte 05 must contain 5a
+ Val 8 = Y axis only. Byte 05 must contain b4
+ Val c = X and Y axes. Bytes 05 must contain 60
+ Bits 0-3: Val 0 = No trigger
+ Val x+1 = Button x triggers the effect
+ When the whole byte is 0, cancel the previously set trigger
+
+ 03-04 Duration of effect (little endian encoding, in ms)
+
+ 05 Direction of effect, if applicable. Else, see 02 for value to assign.
+
+ 06-07 Minimum time between triggering.
+
+ 08-09 Address of periodicity or magnitude parameters
+ 0a-0b Address of attack and fade parameters, or ffff if none.
+ *or*
+ 08-09 Address of interactive parameters for X-axis,
+ or ffff if not applicable
+ 0a-0b Address of interactive parameters for Y-axis,
+ or ffff if not applicable
+
+ 0c-0d Delay before execution of effect (little endian encoding, in ms)
+
+
+Time based parameters
+---------------------
+
+Attack and fade
+^^^^^^^^^^^^^^^
+
+::
+
+ OP= 02
+ LEN= 08
+ 00-01 Address where to store the parameters
+ 02-03 Duration of attack (little endian encoding, in ms)
+ 04 Level at end of attack. Signed byte.
+ 05-06 Duration of fade.
+ 07 Level at end of fade.
+
+Magnitude
+^^^^^^^^^
+
+::
+
+ OP= 03
+ LEN= 03
+ 00-01 Address
+ 02 Level. Signed byte.
+
+Periodicity
+^^^^^^^^^^^
+
+::
+
+ OP= 04
+ LEN= 07
+ 00-01 Address
+ 02 Magnitude. Signed byte.
+ 03 Offset. Signed byte.
+ 04 Phase. Val 00 = 0 deg, Val 40 = 90 degs.
+ 05-06 Period (little endian encoding, in ms)
+
+Interactive parameters
+----------------------
+
+::
+
+ OP= 05
+ LEN= 0a
+ 00-01 Address
+ 02 Positive Coeff
+ 03 Negative Coeff
+ 04+05 Offset (center)
+ 06+07 Dead band (Val 01F4 = 5000 (decimal))
+ 08 Positive saturation (Val 0a = 1000 (decimal) Val 64 = 10000 (decimal))
+ 09 Negative saturation
+
+The encoding is a bit funny here: For coeffs, these are signed values. The
+maximum value is 64 (100 decimal), the min is 9c.
+For the offset, the minimum value is FE0C, the maximum value is 01F4.
+For the deadband, the minimum value is 0, the max is 03E8.
+
+Controls
+--------
+
+::
+
+ OP= 41
+ LEN= 03
+ 00 Channel
+ 01 Start/Stop
+ Val 00: Stop
+ Val 01: Start and play once.
+ Val 41: Start and play n times (See byte 02 below)
+ 02 Number of iterations n.
+
+Init
+----
+
+
+Querying features
+^^^^^^^^^^^^^^^^^
+::
+
+ OP= ff
+ Query command. Length varies according to the query type.
+ The general format of this packet is:
+ ff 01 QUERY [INDEX] CHECKSUM
+ responses are of the same form:
+ FF LEN QUERY VALUE_QUERIED CHECKSUM2
+ where LEN = 1 + length(VALUE_QUERIED)
+
+Query ram size
+~~~~~~~~~~~~~~
+
+::
+
+ QUERY = 42 ('B'uffer size)
+
+The device should reply with the same packet plus two additional bytes
+containing the size of the memory:
+ff 03 42 03 e8 CS would mean that the device has 1000 bytes of ram available.
+
+Query number of effects
+~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+ QUERY = 4e ('N'umber of effects)
+
+The device should respond by sending the number of effects that can be played
+at the same time (one byte)
+ff 02 4e 14 CS would stand for 20 effects.
+
+Vendor's id
+~~~~~~~~~~~
+
+::
+
+ QUERY = 4d ('M'anufacturer)
+
+Query the vendors'id (2 bytes)
+
+Product id
+~~~~~~~~~~
+
+::
+
+ QUERY = 50 ('P'roduct)
+
+Query the product id (2 bytes)
+
+Open device
+~~~~~~~~~~~
+
+::
+
+ QUERY = 4f ('O'pen)
+
+No data returned.
+
+Close device
+~~~~~~~~~~~~
+
+::
+
+ QUERY = 43 ('C')lose
+
+No data returned.
+
+Query effect
+~~~~~~~~~~~~
+
+::
+
+ QUERY = 45 ('E')
+
+Send effect type.
+Returns nonzero if supported (2 bytes)
+
+Firmware Version
+~~~~~~~~~~~~~~~~
+
+::
+
+ QUERY = 56 ('V'ersion)
+
+Sends back 3 bytes - major, minor, subminor
+
+Initialisation of the device
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Set Control
+~~~~~~~~~~~
+
+.. note::
+ Device dependent, can be different on different models!
+
+::
+
+ OP= 40 <idx> <val> [<val>]
+ LEN= 2 or 3
+ 00 Idx
+ Idx 00 Set dead zone (0..2048)
+ Idx 01 Ignore Deadman sensor (0..1)
+ Idx 02 Enable comm watchdog (0..1)
+ Idx 03 Set the strength of the spring (0..100)
+ Idx 04 Enable or disable the spring (0/1)
+ Idx 05 Set axis saturation threshold (0..2048)
+
+Set Effect State
+~~~~~~~~~~~~~~~~
+
+::
+
+ OP= 42 <val>
+ LEN= 1
+ 00 State
+ Bit 3 Pause force feedback
+ Bit 2 Enable force feedback
+ Bit 0 Stop all effects
+
+Set overall
+~~~~~~~~~~~
+
+::
+
+ OP= 43 <val>
+ LEN= 1
+ 00 Gain
+ Val 00 = 0%
+ Val 40 = 50%
+ Val 80 = 100%
+
+Parameter memory
+----------------
+
+Each device has a certain amount of memory to store parameters of effects.
+The amount of RAM may vary, I encountered values from 200 to 1000 bytes. Below
+is the amount of memory apparently needed for every set of parameters:
+
+ - period : 0c
+ - magnitude : 02
+ - attack and fade : 0e
+ - interactive : 08
+
+Appendix: How to study the protocol?
+====================================
+
+1. Generate effects using the force editor provided with the DirectX SDK, or
+use Immersion Studio (freely available at their web site in the developer section:
+www.immersion.com)
+2. Start a soft spying RS232 or USB (depending on where you connected your
+joystick/wheel). I used ComPortSpy from fCoder (alpha version!)
+3. Play the effect, and watch what happens on the spy screen.
+
+A few words about ComPortSpy:
+At first glance, this software seems, hum, well... buggy. In fact, data appear with a
+few seconds latency. Personally, I restart it every time I play an effect.
+Remember it's free (as in free beer) and alpha!
+
+URLS
+====
+
+Check http://www.immerse.com for Immersion Studio,
+and http://www.fcoder.com for ComPortSpy.
+
+
+I-Force is trademark of Immersion Corp.