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+** 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 ****
+!!! 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 gain ****
+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 www.immerse.com for Immersion Studio, and www.fcoder.com for ComPortSpy.
+
+** Author of this document **
+Johann Deneux <johann.deneux@gmail.com>
+Home page at http://web.archive.org/web/*/http://www.esil.univ-mrs.fr
+
+Additions by Vojtech Pavlik.
+
+I-Force is trademark of Immersion Corp.