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A chapter is added to describe the trackpoint packets. A section is added to describe the behaviour of the knob crc_enabled in sysfs. The introduction of the documentation only mentioned v1/v2, but in the last part it already contains explanation of v3 and v4. The introduction is updated. Signed-off-by: Ulrik De Bie <ulrik.debie-os@e2big.org> Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
818 lines
22 KiB
Plaintext
818 lines
22 KiB
Plaintext
Elantech Touchpad Driver
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========================
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Copyright (C) 2007-2008 Arjan Opmeer <arjan@opmeer.net>
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Extra information for hardware version 1 found and
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provided by Steve Havelka
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Version 2 (EeePC) hardware support based on patches
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received from Woody at Xandros and forwarded to me
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by user StewieGriffin at the eeeuser.com forum
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Contents
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~~~~~~~~
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1. Introduction
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2. Extra knobs
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3. Differentiating hardware versions
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4. Hardware version 1
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4.1 Registers
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4.2 Native relative mode 4 byte packet format
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4.3 Native absolute mode 4 byte packet format
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5. Hardware version 2
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5.1 Registers
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5.2 Native absolute mode 6 byte packet format
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5.2.1 Parity checking and packet re-synchronization
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5.2.2 One/Three finger touch
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5.2.3 Two finger touch
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6. Hardware version 3
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6.1 Registers
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6.2 Native absolute mode 6 byte packet format
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6.2.1 One/Three finger touch
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6.2.2 Two finger touch
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7. Hardware version 4
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7.1 Registers
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7.2 Native absolute mode 6 byte packet format
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7.2.1 Status packet
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7.2.2 Head packet
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7.2.3 Motion packet
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8. Trackpoint (for Hardware version 3 and 4)
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8.1 Registers
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8.2 Native relative mode 6 byte packet format
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8.2.1 Status Packet
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1. Introduction
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~~~~~~~~~~~~
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Currently the Linux Elantech touchpad driver is aware of four different
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hardware versions unimaginatively called version 1,version 2, version 3
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and version 4. Version 1 is found in "older" laptops and uses 4 bytes per
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packet. Version 2 seems to be introduced with the EeePC and uses 6 bytes
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per packet, and provides additional features such as position of two fingers,
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and width of the touch. Hardware version 3 uses 6 bytes per packet (and
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for 2 fingers the concatenation of two 6 bytes packets) and allows tracking
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of up to 3 fingers. Hardware version 4 uses 6 bytes per packet, and can
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combine a status packet with multiple head or motion packets. Hardware version
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4 allows tracking up to 5 fingers.
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Some Hardware version 3 and version 4 also have a trackpoint which uses a
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separate packet format. It is also 6 bytes per packet.
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The driver tries to support both hardware versions and should be compatible
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with the Xorg Synaptics touchpad driver and its graphical configuration
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utilities.
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Note that a mouse button is also associated with either the touchpad or the
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trackpoint when a trackpoint is available. Disabling the Touchpad in xorg
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(TouchPadOff=0) will also disable the buttons associated with the touchpad.
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Additionally the operation of the touchpad can be altered by adjusting the
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contents of some of its internal registers. These registers are represented
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by the driver as sysfs entries under /sys/bus/serio/drivers/psmouse/serio?
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that can be read from and written to.
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Currently only the registers for hardware version 1 are somewhat understood.
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Hardware version 2 seems to use some of the same registers but it is not
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known whether the bits in the registers represent the same thing or might
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have changed their meaning.
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On top of that, some register settings have effect only when the touchpad is
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in relative mode and not in absolute mode. As the Linux Elantech touchpad
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driver always puts the hardware into absolute mode not all information
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mentioned below can be used immediately. But because there is no freely
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available Elantech documentation the information is provided here anyway for
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completeness sake.
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/////////////////////////////////////////////////////////////////////////////
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2. Extra knobs
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~~~~~~~~~~~
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Currently the Linux Elantech touchpad driver provides three extra knobs under
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/sys/bus/serio/drivers/psmouse/serio? for the user.
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* debug
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Turn different levels of debugging ON or OFF.
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By echoing "0" to this file all debugging will be turned OFF.
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Currently a value of "1" will turn on some basic debugging and a value of
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"2" will turn on packet debugging. For hardware version 1 the default is
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OFF. For version 2 the default is "1".
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Turning packet debugging on will make the driver dump every packet
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received to the syslog before processing it. Be warned that this can
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generate quite a lot of data!
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* paritycheck
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Turns parity checking ON or OFF.
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By echoing "0" to this file parity checking will be turned OFF. Any
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non-zero value will turn it ON. For hardware version 1 the default is ON.
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For version 2 the default it is OFF.
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Hardware version 1 provides basic data integrity verification by
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calculating a parity bit for the last 3 bytes of each packet. The driver
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can check these bits and reject any packet that appears corrupted. Using
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this knob you can bypass that check.
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Hardware version 2 does not provide the same parity bits. Only some basic
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data consistency checking can be done. For now checking is disabled by
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default. Currently even turning it on will do nothing.
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* crc_enabled
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Sets crc_enabled to 0/1. The name "crc_enabled" is the official name of
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this integrity check, even though it is not an actual cyclic redundancy
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check.
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Depending on the state of crc_enabled, certain basic data integrity
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verification is done by the driver on hardware version 3 and 4. The
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driver will reject any packet that appears corrupted. Using this knob,
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The state of crc_enabled can be altered with this knob.
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Reading the crc_enabled value will show the active value. Echoing
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"0" or "1" to this file will set the state to "0" or "1".
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/////////////////////////////////////////////////////////////////////////////
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3. Differentiating hardware versions
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=================================
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To detect the hardware version, read the version number as param[0].param[1].param[2]
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4 bytes version: (after the arrow is the name given in the Dell-provided driver)
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02.00.22 => EF013
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02.06.00 => EF019
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In the wild, there appear to be more versions, such as 00.01.64, 01.00.21,
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02.00.00, 02.00.04, 02.00.06.
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6 bytes:
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02.00.30 => EF113
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02.08.00 => EF023
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02.08.XX => EF123
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02.0B.00 => EF215
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04.01.XX => Scroll_EF051
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04.02.XX => EF051
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In the wild, there appear to be more versions, such as 04.03.01, 04.04.11. There
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appears to be almost no difference, except for EF113, which does not report
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pressure/width and has different data consistency checks.
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Probably all the versions with param[0] <= 01 can be considered as
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4 bytes/firmware 1. The versions < 02.08.00, with the exception of 02.00.30, as
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4 bytes/firmware 2. Everything >= 02.08.00 can be considered as 6 bytes.
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/////////////////////////////////////////////////////////////////////////////
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4. Hardware version 1
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==================
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4.1 Registers
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~~~~~~~~~
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By echoing a hexadecimal value to a register it contents can be altered.
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For example:
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echo -n 0x16 > reg_10
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* reg_10
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bit 7 6 5 4 3 2 1 0
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B C T D L A S E
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E: 1 = enable smart edges unconditionally
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S: 1 = enable smart edges only when dragging
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A: 1 = absolute mode (needs 4 byte packets, see reg_11)
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L: 1 = enable drag lock (see reg_22)
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D: 1 = disable dynamic resolution
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T: 1 = disable tapping
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C: 1 = enable corner tap
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B: 1 = swap left and right button
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* reg_11
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bit 7 6 5 4 3 2 1 0
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1 0 0 H V 1 F P
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P: 1 = enable parity checking for relative mode
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F: 1 = enable native 4 byte packet mode
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V: 1 = enable vertical scroll area
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H: 1 = enable horizontal scroll area
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* reg_20
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single finger width?
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* reg_21
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scroll area width (small: 0x40 ... wide: 0xff)
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* reg_22
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drag lock time out (short: 0x14 ... long: 0xfe;
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0xff = tap again to release)
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* reg_23
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tap make timeout?
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* reg_24
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tap release timeout?
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* reg_25
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smart edge cursor speed (0x02 = slow, 0x03 = medium, 0x04 = fast)
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* reg_26
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smart edge activation area width?
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4.2 Native relative mode 4 byte packet format
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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byte 0:
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bit 7 6 5 4 3 2 1 0
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c c p2 p1 1 M R L
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L, R, M = 1 when Left, Right, Middle mouse button pressed
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some models have M as byte 3 odd parity bit
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when parity checking is enabled (reg_11, P = 1):
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p1..p2 = byte 1 and 2 odd parity bit
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c = 1 when corner tap detected
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byte 1:
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bit 7 6 5 4 3 2 1 0
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dx7 dx6 dx5 dx4 dx3 dx2 dx1 dx0
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dx7..dx0 = x movement; positive = right, negative = left
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byte 1 = 0xf0 when corner tap detected
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byte 2:
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bit 7 6 5 4 3 2 1 0
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dy7 dy6 dy5 dy4 dy3 dy2 dy1 dy0
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dy7..dy0 = y movement; positive = up, negative = down
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byte 3:
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parity checking enabled (reg_11, P = 1):
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bit 7 6 5 4 3 2 1 0
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w h n1 n0 ds3 ds2 ds1 ds0
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normally:
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ds3..ds0 = scroll wheel amount and direction
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positive = down or left
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negative = up or right
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when corner tap detected:
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ds0 = 1 when top right corner tapped
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ds1 = 1 when bottom right corner tapped
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ds2 = 1 when bottom left corner tapped
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ds3 = 1 when top left corner tapped
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n1..n0 = number of fingers on touchpad
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only models with firmware 2.x report this, models with
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firmware 1.x seem to map one, two and three finger taps
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directly to L, M and R mouse buttons
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h = 1 when horizontal scroll action
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w = 1 when wide finger touch?
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otherwise (reg_11, P = 0):
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bit 7 6 5 4 3 2 1 0
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ds7 ds6 ds5 ds4 ds3 ds2 ds1 ds0
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ds7..ds0 = vertical scroll amount and direction
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negative = up
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positive = down
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4.3 Native absolute mode 4 byte packet format
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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EF013 and EF019 have a special behaviour (due to a bug in the firmware?), and
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when 1 finger is touching, the first 2 position reports must be discarded.
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This counting is reset whenever a different number of fingers is reported.
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byte 0:
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firmware version 1.x:
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bit 7 6 5 4 3 2 1 0
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D U p1 p2 1 p3 R L
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L, R = 1 when Left, Right mouse button pressed
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p1..p3 = byte 1..3 odd parity bit
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D, U = 1 when rocker switch pressed Up, Down
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firmware version 2.x:
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bit 7 6 5 4 3 2 1 0
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n1 n0 p2 p1 1 p3 R L
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L, R = 1 when Left, Right mouse button pressed
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p1..p3 = byte 1..3 odd parity bit
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n1..n0 = number of fingers on touchpad
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byte 1:
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firmware version 1.x:
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bit 7 6 5 4 3 2 1 0
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f 0 th tw x9 x8 y9 y8
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tw = 1 when two finger touch
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th = 1 when three finger touch
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f = 1 when finger touch
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firmware version 2.x:
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bit 7 6 5 4 3 2 1 0
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. . . . x9 x8 y9 y8
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byte 2:
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bit 7 6 5 4 3 2 1 0
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x7 x6 x5 x4 x3 x2 x1 x0
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x9..x0 = absolute x value (horizontal)
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byte 3:
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bit 7 6 5 4 3 2 1 0
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y7 y6 y5 y4 y3 y2 y1 y0
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y9..y0 = absolute y value (vertical)
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/////////////////////////////////////////////////////////////////////////////
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5. Hardware version 2
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==================
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5.1 Registers
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~~~~~~~~~
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By echoing a hexadecimal value to a register it contents can be altered.
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For example:
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echo -n 0x56 > reg_10
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* reg_10
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bit 7 6 5 4 3 2 1 0
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0 1 0 1 0 1 D 0
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D: 1 = enable drag and drop
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* reg_11
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bit 7 6 5 4 3 2 1 0
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1 0 0 0 S 0 1 0
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S: 1 = enable vertical scroll
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* reg_21
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unknown (0x00)
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* reg_22
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drag and drop release time out (short: 0x70 ... long 0x7e;
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0x7f = never i.e. tap again to release)
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5.2 Native absolute mode 6 byte packet format
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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5.2.1 Parity checking and packet re-synchronization
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There is no parity checking, however some consistency checks can be performed.
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For instance for EF113:
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SA1= packet[0];
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A1 = packet[1];
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B1 = packet[2];
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SB1= packet[3];
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C1 = packet[4];
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D1 = packet[5];
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if( (((SA1 & 0x3C) != 0x3C) && ((SA1 & 0xC0) != 0x80)) || // check Byte 1
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(((SA1 & 0x0C) != 0x0C) && ((SA1 & 0xC0) == 0x80)) || // check Byte 1 (one finger pressed)
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(((SA1 & 0xC0) != 0x80) && (( A1 & 0xF0) != 0x00)) || // check Byte 2
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(((SB1 & 0x3E) != 0x38) && ((SA1 & 0xC0) != 0x80)) || // check Byte 4
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(((SB1 & 0x0E) != 0x08) && ((SA1 & 0xC0) == 0x80)) || // check Byte 4 (one finger pressed)
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(((SA1 & 0xC0) != 0x80) && (( C1 & 0xF0) != 0x00)) ) // check Byte 5
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// error detected
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For all the other ones, there are just a few constant bits:
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if( ((packet[0] & 0x0C) != 0x04) ||
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((packet[3] & 0x0f) != 0x02) )
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// error detected
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In case an error is detected, all the packets are shifted by one (and packet[0] is discarded).
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5.2.2 One/Three finger touch
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~~~~~~~~~~~~~~~~
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byte 0:
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bit 7 6 5 4 3 2 1 0
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n1 n0 w3 w2 . . R L
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L, R = 1 when Left, Right mouse button pressed
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n1..n0 = number of fingers on touchpad
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byte 1:
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bit 7 6 5 4 3 2 1 0
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p7 p6 p5 p4 x11 x10 x9 x8
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byte 2:
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bit 7 6 5 4 3 2 1 0
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x7 x6 x5 x4 x3 x2 x1 x0
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x11..x0 = absolute x value (horizontal)
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byte 3:
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bit 7 6 5 4 3 2 1 0
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n4 vf w1 w0 . . . b2
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n4 = set if more than 3 fingers (only in 3 fingers mode)
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vf = a kind of flag ? (only on EF123, 0 when finger is over one
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of the buttons, 1 otherwise)
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w3..w0 = width of the finger touch (not EF113)
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b2 (on EF113 only, 0 otherwise), b2.R.L indicates one button pressed:
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0 = none
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1 = Left
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2 = Right
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3 = Middle (Left and Right)
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4 = Forward
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5 = Back
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6 = Another one
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7 = Another one
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byte 4:
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bit 7 6 5 4 3 2 1 0
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p3 p1 p2 p0 y11 y10 y9 y8
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p7..p0 = pressure (not EF113)
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byte 5:
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bit 7 6 5 4 3 2 1 0
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y7 y6 y5 y4 y3 y2 y1 y0
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y11..y0 = absolute y value (vertical)
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5.2.3 Two finger touch
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~~~~~~~~~~~~~~~~
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Note that the two pairs of coordinates are not exactly the coordinates of the
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two fingers, but only the pair of the lower-left and upper-right coordinates.
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So the actual fingers might be situated on the other diagonal of the square
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defined by these two points.
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byte 0:
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bit 7 6 5 4 3 2 1 0
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n1 n0 ay8 ax8 . . R L
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L, R = 1 when Left, Right mouse button pressed
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n1..n0 = number of fingers on touchpad
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byte 1:
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bit 7 6 5 4 3 2 1 0
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ax7 ax6 ax5 ax4 ax3 ax2 ax1 ax0
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ax8..ax0 = lower-left finger absolute x value
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byte 2:
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bit 7 6 5 4 3 2 1 0
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ay7 ay6 ay5 ay4 ay3 ay2 ay1 ay0
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ay8..ay0 = lower-left finger absolute y value
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byte 3:
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bit 7 6 5 4 3 2 1 0
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. . by8 bx8 . . . .
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byte 4:
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bit 7 6 5 4 3 2 1 0
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bx7 bx6 bx5 bx4 bx3 bx2 bx1 bx0
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bx8..bx0 = upper-right finger absolute x value
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byte 5:
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bit 7 6 5 4 3 2 1 0
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by7 by8 by5 by4 by3 by2 by1 by0
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by8..by0 = upper-right finger absolute y value
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/////////////////////////////////////////////////////////////////////////////
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6. Hardware version 3
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==================
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6.1 Registers
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~~~~~~~~~
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* reg_10
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bit 7 6 5 4 3 2 1 0
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0 0 0 0 R F T A
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A: 1 = enable absolute tracking
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T: 1 = enable two finger mode auto correct
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F: 1 = disable ABS Position Filter
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R: 1 = enable real hardware resolution
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6.2 Native absolute mode 6 byte packet format
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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1 and 3 finger touch shares the same 6-byte packet format, except that
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3 finger touch only reports the position of the center of all three fingers.
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Firmware would send 12 bytes of data for 2 finger touch.
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Note on debounce:
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In case the box has unstable power supply or other electricity issues, or
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when number of finger changes, F/W would send "debounce packet" to inform
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driver that the hardware is in debounce status.
|
|
The debouce packet has the following signature:
|
|
byte 0: 0xc4
|
|
byte 1: 0xff
|
|
byte 2: 0xff
|
|
byte 3: 0x02
|
|
byte 4: 0xff
|
|
byte 5: 0xff
|
|
When we encounter this kind of packet, we just ignore it.
|
|
|
|
6.2.1 One/Three finger touch
|
|
~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
byte 0:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
n1 n0 w3 w2 0 1 R L
|
|
|
|
L, R = 1 when Left, Right mouse button pressed
|
|
n1..n0 = number of fingers on touchpad
|
|
|
|
byte 1:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
p7 p6 p5 p4 x11 x10 x9 x8
|
|
|
|
byte 2:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
x7 x6 x5 x4 x3 x2 x1 x0
|
|
|
|
x11..x0 = absolute x value (horizontal)
|
|
|
|
byte 3:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
0 0 w1 w0 0 0 1 0
|
|
|
|
w3..w0 = width of the finger touch
|
|
|
|
byte 4:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
p3 p1 p2 p0 y11 y10 y9 y8
|
|
|
|
p7..p0 = pressure
|
|
|
|
byte 5:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
y7 y6 y5 y4 y3 y2 y1 y0
|
|
|
|
y11..y0 = absolute y value (vertical)
|
|
|
|
6.2.2 Two finger touch
|
|
~~~~~~~~~~~~~~~~
|
|
|
|
The packet format is exactly the same for two finger touch, except the hardware
|
|
sends two 6 byte packets. The first packet contains data for the first finger,
|
|
the second packet has data for the second finger. So for two finger touch a
|
|
total of 12 bytes are sent.
|
|
|
|
/////////////////////////////////////////////////////////////////////////////
|
|
|
|
7. Hardware version 4
|
|
==================
|
|
|
|
7.1 Registers
|
|
~~~~~~~~~
|
|
* reg_07
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
0 0 0 0 0 0 0 A
|
|
|
|
A: 1 = enable absolute tracking
|
|
|
|
7.2 Native absolute mode 6 byte packet format
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
v4 hardware is a true multitouch touchpad, capable of tracking up to 5 fingers.
|
|
Unfortunately, due to PS/2's limited bandwidth, its packet format is rather
|
|
complex.
|
|
|
|
Whenever the numbers or identities of the fingers changes, the hardware sends a
|
|
status packet to indicate how many and which fingers is on touchpad, followed by
|
|
head packets or motion packets. A head packet contains data of finger id, finger
|
|
position (absolute x, y values), width, and pressure. A motion packet contains
|
|
two fingers' position delta.
|
|
|
|
For example, when status packet tells there are 2 fingers on touchpad, then we
|
|
can expect two following head packets. If the finger status doesn't change,
|
|
the following packets would be motion packets, only sending delta of finger
|
|
position, until we receive a status packet.
|
|
|
|
One exception is one finger touch. when a status packet tells us there is only
|
|
one finger, the hardware would just send head packets afterwards.
|
|
|
|
7.2.1 Status packet
|
|
~~~~~~~~~~~~~
|
|
|
|
byte 0:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
. . . . 0 1 R L
|
|
|
|
L, R = 1 when Left, Right mouse button pressed
|
|
|
|
byte 1:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
. . . ft4 ft3 ft2 ft1 ft0
|
|
|
|
ft4 ft3 ft2 ft1 ft0 ftn = 1 when finger n is on touchpad
|
|
|
|
byte 2: not used
|
|
|
|
byte 3:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
. . . 1 0 0 0 0
|
|
|
|
constant bits
|
|
|
|
byte 4:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
p . . . . . . .
|
|
|
|
p = 1 for palm
|
|
|
|
byte 5: not used
|
|
|
|
7.2.2 Head packet
|
|
~~~~~~~~~~~
|
|
|
|
byte 0:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
w3 w2 w1 w0 0 1 R L
|
|
|
|
L, R = 1 when Left, Right mouse button pressed
|
|
w3..w0 = finger width (spans how many trace lines)
|
|
|
|
byte 1:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
p7 p6 p5 p4 x11 x10 x9 x8
|
|
|
|
byte 2:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
x7 x6 x5 x4 x3 x2 x1 x0
|
|
|
|
x11..x0 = absolute x value (horizontal)
|
|
|
|
byte 3:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
id2 id1 id0 1 0 0 0 1
|
|
|
|
id2..id0 = finger id
|
|
|
|
byte 4:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
p3 p1 p2 p0 y11 y10 y9 y8
|
|
|
|
p7..p0 = pressure
|
|
|
|
byte 5:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
y7 y6 y5 y4 y3 y2 y1 y0
|
|
|
|
y11..y0 = absolute y value (vertical)
|
|
|
|
7.2.3 Motion packet
|
|
~~~~~~~~~~~~~
|
|
|
|
byte 0:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
id2 id1 id0 w 0 1 R L
|
|
|
|
L, R = 1 when Left, Right mouse button pressed
|
|
id2..id0 = finger id
|
|
w = 1 when delta overflows (> 127 or < -128), in this case
|
|
firmware sends us (delta x / 5) and (delta y / 5)
|
|
|
|
byte 1:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
x7 x6 x5 x4 x3 x2 x1 x0
|
|
|
|
x7..x0 = delta x (two's complement)
|
|
|
|
byte 2:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
y7 y6 y5 y4 y3 y2 y1 y0
|
|
|
|
y7..y0 = delta y (two's complement)
|
|
|
|
byte 3:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
id2 id1 id0 1 0 0 1 0
|
|
|
|
id2..id0 = finger id
|
|
|
|
byte 4:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
x7 x6 x5 x4 x3 x2 x1 x0
|
|
|
|
x7..x0 = delta x (two's complement)
|
|
|
|
byte 5:
|
|
|
|
bit 7 6 5 4 3 2 1 0
|
|
y7 y6 y5 y4 y3 y2 y1 y0
|
|
|
|
y7..y0 = delta y (two's complement)
|
|
|
|
byte 0 ~ 2 for one finger
|
|
byte 3 ~ 5 for another
|
|
|
|
|
|
8. Trackpoint (for Hardware version 3 and 4)
|
|
=========================================
|
|
8.1 Registers
|
|
~~~~~~~~~
|
|
No special registers have been identified.
|
|
|
|
8.2 Native relative mode 6 byte packet format
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
8.2.1 Status Packet
|
|
~~~~~~~~~~~~~
|
|
|
|
byte 0:
|
|
bit 7 6 5 4 3 2 1 0
|
|
0 0 sx sy 0 M R L
|
|
byte 1:
|
|
bit 7 6 5 4 3 2 1 0
|
|
~sx 0 0 0 0 0 0 0
|
|
byte 2:
|
|
bit 7 6 5 4 3 2 1 0
|
|
~sy 0 0 0 0 0 0 0
|
|
byte 3:
|
|
bit 7 6 5 4 3 2 1 0
|
|
0 0 ~sy ~sx 0 1 1 0
|
|
byte 4:
|
|
bit 7 6 5 4 3 2 1 0
|
|
x7 x6 x5 x4 x3 x2 x1 x0
|
|
byte 5:
|
|
bit 7 6 5 4 3 2 1 0
|
|
y7 y6 y5 y4 y3 y2 y1 y0
|
|
|
|
|
|
x and y are written in two's complement spread
|
|
over 9 bits with sx/sy the relative top bit and
|
|
x7..x0 and y7..y0 the lower bits.
|
|
~sx is the inverse of sx, ~sy is the inverse of sy.
|
|
The sign of y is opposite to what the input driver
|
|
expects for a relative movement
|