Documentation/input/elantech.txt

   1 Elantech Touchpad Driver
   2 ========================
   3
   4         Copyright (C) 2007-2008 Arjan Opmeer <arjan@opmeer.net>
   5
   6         Extra information for hardware version 1 found and
   7         provided by Steve Havelka
   8
   9         Version 2 (EeePC) hardware support based on patches
  10         received from Woody at Xandros and forwarded to me
  11         by user StewieGriffin at the eeeuser.com forum
  12
  13
  14 Contents
  15 ~~~~~~~~
  16
  17  1. Introduction
  18  2. Extra knobs
  19  3. Differentiating hardware versions
  20  4. Hardware version 1
  21     4.1 Registers
  22     4.2 Native relative mode 4 byte packet format
  23     4.3 Native absolute mode 4 byte packet format
  24  5. Hardware version 2
  25     5.1 Registers
  26     5.2 Native absolute mode 6 byte packet format
  27         5.2.1 Parity checking and packet re-synchronization
  28         5.2.2 One/Three finger touch
  29         5.2.3 Two finger touch
  30  6. Hardware version 3
  31     6.1 Registers
  32     6.2 Native absolute mode 6 byte packet format
  33         6.2.1 One/Three finger touch
  34         6.2.2 Two finger touch
  35  7. Hardware version 4
  36     7.1 Registers
  37     7.2 Native absolute mode 6 byte packet format
  38         7.2.1 Status packet
  39         7.2.2 Head packet
  40         7.2.3 Motion packet
  41
  42
  43
  44 1. Introduction
  45    ~~~~~~~~~~~~
  46
  47 Currently the Linux Elantech touchpad driver is aware of two different
  48 hardware versions unimaginatively called version 1 and version 2. Version 1
  49 is found in "older" laptops and uses 4 bytes per packet. Version 2 seems to
  50 be introduced with the EeePC and uses 6 bytes per packet, and provides
  51 additional features such as position of two fingers, and width of the touch.
  52
  53 The driver tries to support both hardware versions and should be compatible
  54 with the Xorg Synaptics touchpad driver and its graphical configuration
  55 utilities.
  56
  57 Additionally the operation of the touchpad can be altered by adjusting the
  58 contents of some of its internal registers. These registers are represented
  59 by the driver as sysfs entries under /sys/bus/serio/drivers/psmouse/serio?
  60 that can be read from and written to.
  61
  62 Currently only the registers for hardware version 1 are somewhat understood.
  63 Hardware version 2 seems to use some of the same registers but it is not
  64 known whether the bits in the registers represent the same thing or might
  65 have changed their meaning.
  66
  67 On top of that, some register settings have effect only when the touchpad is
  68 in relative mode and not in absolute mode. As the Linux Elantech touchpad
  69 driver always puts the hardware into absolute mode not all information
  70 mentioned below can be used immediately. But because there is no freely
  71 available Elantech documentation the information is provided here anyway for
  72 completeness sake.
  73
  74
  75 /////////////////////////////////////////////////////////////////////////////
  76
  77
  78 2. Extra knobs
  79    ~~~~~~~~~~~
  80
  81 Currently the Linux Elantech touchpad driver provides two extra knobs under
  82 /sys/bus/serio/drivers/psmouse/serio? for the user.
  83
  84 * debug
  85
  86    Turn different levels of debugging ON or OFF.
  87
  88    By echoing "0" to this file all debugging will be turned OFF.
  89
  90    Currently a value of "1" will turn on some basic debugging and a value of
  91    "2" will turn on packet debugging. For hardware version 1 the default is
  92    OFF. For version 2 the default is "1".
  93
  94    Turning packet debugging on will make the driver dump every packet
  95    received to the syslog before processing it. Be warned that this can
  96    generate quite a lot of data!
  97
  98 * paritycheck
  99
 100    Turns parity checking ON or OFF.
 101
 102    By echoing "0" to this file parity checking will be turned OFF. Any
 103    non-zero value will turn it ON. For hardware version 1 the default is ON.
 104    For version 2 the default it is OFF.
 105
 106    Hardware version 1 provides basic data integrity verification by
 107    calculating a parity bit for the last 3 bytes of each packet. The driver
 108    can check these bits and reject any packet that appears corrupted. Using
 109    this knob you can bypass that check.
 110
 111    Hardware version 2 does not provide the same parity bits. Only some basic
 112    data consistency checking can be done. For now checking is disabled by
 113    default. Currently even turning it on will do nothing.
 114
 115 /////////////////////////////////////////////////////////////////////////////
 116
 117 3. Differentiating hardware versions
 118    =================================
 119
 120 To detect the hardware version, read the version number as param[0].param[1].param[2]
 121
 122  4 bytes version: (after the arrow is the name given in the Dell-provided driver)
 123  02.00.22 => EF013
 124  02.06.00 => EF019
 125 In the wild, there appear to be more versions, such as 00.01.64, 01.00.21,
 126 02.00.00, 02.00.04, 02.00.06.
 127
 128  6 bytes:
 129  02.00.30 => EF113
 130  02.08.00 => EF023
 131  02.08.XX => EF123
 132  02.0B.00 => EF215
 133  04.01.XX => Scroll_EF051
 134  04.02.XX => EF051
 135 In the wild, there appear to be more versions, such as 04.03.01, 04.04.11. There
 136 appears to be almost no difference, except for EF113, which does not report
 137 pressure/width and has different data consistency checks.
 138
 139 Probably all the versions with param[0] <= 01 can be considered as
 140 4 bytes/firmware 1. The versions < 02.08.00, with the exception of 02.00.30, as
 141 4 bytes/firmware 2. Everything >= 02.08.00 can be considered as 6 bytes.
 142
 143 /////////////////////////////////////////////////////////////////////////////
 144
 145 4. Hardware version 1
 146    ==================
 147
 148 4.1 Registers
 149     ~~~~~~~~~
 150
 151 By echoing a hexadecimal value to a register it contents can be altered.
 152
 153 For example:
 154
 155    echo -n 0x16 > reg_10
 156
 157 * reg_10
 158
 159    bit   7   6   5   4   3   2   1   0
 160          B   C   T   D   L   A   S   E
 161
 162          E: 1 = enable smart edges unconditionally
 163          S: 1 = enable smart edges only when dragging
 164          A: 1 = absolute mode (needs 4 byte packets, see reg_11)
 165          L: 1 = enable drag lock (see reg_22)
 166          D: 1 = disable dynamic resolution
 167          T: 1 = disable tapping
 168          C: 1 = enable corner tap
 169          B: 1 = swap left and right button
 170
 171 * reg_11
 172
 173    bit   7   6   5   4   3   2   1   0
 174          1   0   0   H   V   1   F   P
 175
 176          P: 1 = enable parity checking for relative mode
 177          F: 1 = enable native 4 byte packet mode
 178          V: 1 = enable vertical scroll area
 179          H: 1 = enable horizontal scroll area
 180
 181 * reg_20
 182
 183          single finger width?
 184
 185 * reg_21
 186
 187          scroll area width (small: 0x40 ... wide: 0xff)
 188
 189 * reg_22
 190
 191          drag lock time out (short: 0x14 ... long: 0xfe;
 192                              0xff = tap again to release)
 193
 194 * reg_23
 195
 196          tap make timeout?
 197
 198 * reg_24
 199
 200          tap release timeout?
 201
 202 * reg_25
 203
 204          smart edge cursor speed (0x02 = slow, 0x03 = medium, 0x04 = fast)
 205
 206 * reg_26
 207
 208          smart edge activation area width?
 209
 210
 211 4.2 Native relative mode 4 byte packet format
 212     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 213
 214 byte 0:
 215    bit   7   6   5   4   3   2   1   0
 216          c   c  p2  p1   1   M   R   L
 217
 218          L, R, M = 1 when Left, Right, Middle mouse button pressed
 219             some models have M as byte 3 odd parity bit
 220          when parity checking is enabled (reg_11, P = 1):
 221             p1..p2 = byte 1 and 2 odd parity bit
 222          c = 1 when corner tap detected
 223
 224 byte 1:
 225    bit   7   6   5   4   3   2   1   0
 226         dx7 dx6 dx5 dx4 dx3 dx2 dx1 dx0
 227
 228          dx7..dx0 = x movement;   positive = right, negative = left
 229          byte 1 = 0xf0 when corner tap detected
 230
 231 byte 2:
 232    bit   7   6   5   4   3   2   1   0
 233         dy7 dy6 dy5 dy4 dy3 dy2 dy1 dy0
 234
 235          dy7..dy0 = y movement;   positive = up,    negative = down
 236
 237 byte 3:
 238    parity checking enabled (reg_11, P = 1):
 239
 240       bit   7   6   5   4   3   2   1   0
 241             w   h  n1  n0  ds3 ds2 ds1 ds0
 242
 243             normally:
 244                ds3..ds0 = scroll wheel amount and direction
 245                           positive = down or left
 246                           negative = up or right
 247             when corner tap detected:
 248                ds0 = 1 when top right corner tapped
 249                ds1 = 1 when bottom right corner tapped
 250                ds2 = 1 when bottom left corner tapped
 251                ds3 = 1 when top left corner tapped
 252             n1..n0 = number of fingers on touchpad
 253                only models with firmware 2.x report this, models with
 254                firmware 1.x seem to map one, two and three finger taps
 255                directly to L, M and R mouse buttons
 256             h = 1 when horizontal scroll action
 257             w = 1 when wide finger touch?
 258
 259    otherwise (reg_11, P = 0):
 260
 261       bit   7   6   5   4   3   2   1   0
 262            ds7 ds6 ds5 ds4 ds3 ds2 ds1 ds0
 263
 264             ds7..ds0 = vertical scroll amount and direction
 265                        negative = up
 266                        positive = down
 267
 268
 269 4.3 Native absolute mode 4 byte packet format
 270     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 271
 272 EF013 and EF019 have a special behaviour (due to a bug in the firmware?), and
 273 when 1 finger is touching, the first 2 position reports must be discarded.
 274 This counting is reset whenever a different number of fingers is reported.
 275
 276 byte 0:
 277    firmware version 1.x:
 278
 279       bit   7   6   5   4   3   2   1   0
 280             D   U  p1  p2   1  p3   R   L
 281
 282             L, R = 1 when Left, Right mouse button pressed
 283             p1..p3 = byte 1..3 odd parity bit
 284             D, U = 1 when rocker switch pressed Up, Down
 285
 286    firmware version 2.x:
 287
 288       bit   7   6   5   4   3   2   1   0
 289            n1  n0  p2  p1   1  p3   R   L
 290
 291             L, R = 1 when Left, Right mouse button pressed
 292             p1..p3 = byte 1..3 odd parity bit
 293             n1..n0 = number of fingers on touchpad
 294
 295 byte 1:
 296    firmware version 1.x:
 297
 298       bit   7   6   5   4   3   2   1   0
 299             f   0  th  tw  x9  x8  y9  y8
 300
 301             tw = 1 when two finger touch
 302             th = 1 when three finger touch
 303             f  = 1 when finger touch
 304
 305    firmware version 2.x:
 306
 307       bit   7   6   5   4   3   2   1   0
 308             .   .   .   .  x9  x8  y9  y8
 309
 310 byte 2:
 311    bit   7   6   5   4   3   2   1   0
 312         x7  x6  x5  x4  x3  x2  x1  x0
 313
 314          x9..x0 = absolute x value (horizontal)
 315
 316 byte 3:
 317    bit   7   6   5   4   3   2   1   0
 318         y7  y6  y5  y4  y3  y2  y1  y0
 319
 320          y9..y0 = absolute y value (vertical)
 321
 322
 323 /////////////////////////////////////////////////////////////////////////////
 324
 325
 326 5. Hardware version 2
 327    ==================
 328
 329
 330 5.1 Registers
 331     ~~~~~~~~~
 332
 333 By echoing a hexadecimal value to a register it contents can be altered.
 334
 335 For example:
 336
 337    echo -n 0x56 > reg_10
 338
 339 * reg_10
 340
 341    bit   7   6   5   4   3   2   1   0
 342          0   1   0   1   0   1   D   0
 343
 344          D: 1 = enable drag and drop
 345
 346 * reg_11
 347
 348    bit   7   6   5   4   3   2   1   0
 349          1   0   0   0   S   0   1   0
 350
 351          S: 1 = enable vertical scroll
 352
 353 * reg_21
 354
 355          unknown (0x00)
 356
 357 * reg_22
 358
 359          drag and drop release time out (short: 0x70 ... long 0x7e;
 360                                    0x7f = never i.e. tap again to release)
 361
 362
 363 5.2 Native absolute mode 6 byte packet format
 364     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 365 5.2.1 Parity checking and packet re-synchronization
 366 There is no parity checking, however some consistency checks can be performed.
 367
 368 For instance for EF113:
 369         SA1= packet[0];
 370         A1 = packet[1];
 371         B1 = packet[2];
 372         SB1= packet[3];
 373         C1 = packet[4];
 374         D1 = packet[5];
 375         if( (((SA1 & 0x3C) != 0x3C) && ((SA1 & 0xC0) != 0x80)) || // check Byte 1
 376             (((SA1 & 0x0C) != 0x0C) && ((SA1 & 0xC0) == 0x80)) || // check Byte 1 (one finger pressed)
 377             (((SA1 & 0xC0) != 0x80) && (( A1 & 0xF0) != 0x00)) || // check Byte 2
 378             (((SB1 & 0x3E) != 0x38) && ((SA1 & 0xC0) != 0x80)) || // check Byte 4
 379             (((SB1 & 0x0E) != 0x08) && ((SA1 & 0xC0) == 0x80)) || // check Byte 4 (one finger pressed)
 380             (((SA1 & 0xC0) != 0x80) && (( C1 & 0xF0) != 0x00))  ) // check Byte 5
 381                 // error detected
 382
 383 For all the other ones, there are just a few constant bits:
 384         if( ((packet[0] & 0x0C) != 0x04) ||
 385             ((packet[3] & 0x0f) != 0x02) )
 386                 // error detected
 387
 388
 389 In case an error is detected, all the packets are shifted by one (and packet[0] is discarded).
 390
 391 5.2.2 One/Three finger touch
 392       ~~~~~~~~~~~~~~~~
 393
 394 byte 0:
 395
 396    bit   7   6   5   4   3   2   1   0
 397          n1  n0  w3  w2   .   .   R   L
 398
 399          L, R = 1 when Left, Right mouse button pressed
 400          n1..n0 = number of fingers on touchpad
 401
 402 byte 1:
 403
 404    bit   7   6   5   4   3   2   1   0
 405          p7  p6  p5  p4 x11 x10 x9  x8
 406
 407 byte 2:
 408
 409    bit   7   6   5   4   3   2   1   0
 410          x7  x6  x5  x4  x3  x2  x1  x0
 411
 412          x11..x0 = absolute x value (horizontal)
 413
 414 byte 3:
 415
 416    bit   7   6   5   4   3   2   1   0
 417          n4  vf  w1  w0   .   .   .  b2
 418
 419          n4 = set if more than 3 fingers (only in 3 fingers mode)
 420          vf = a kind of flag ? (only on EF123, 0 when finger is over one
 421               of the buttons, 1 otherwise)
 422          w3..w0 = width of the finger touch (not EF113)
 423          b2 (on EF113 only, 0 otherwise), b2.R.L indicates one button pressed:
 424                 0 = none
 425                 1 = Left
 426                 2 = Right
 427                 3 = Middle (Left and Right)
 428                 4 = Forward
 429                 5 = Back
 430                 6 = Another one
 431                 7 = Another one
 432
 433 byte 4:
 434
 435    bit   7   6   5   4   3   2   1   0
 436         p3  p1  p2  p0  y11 y10 y9  y8
 437
 438          p7..p0 = pressure (not EF113)
 439
 440 byte 5:
 441
 442    bit   7   6   5   4   3   2   1   0
 443         y7  y6  y5  y4  y3  y2  y1  y0
 444
 445          y11..y0 = absolute y value (vertical)
 446
 447
 448 5.2.3 Two finger touch
 449       ~~~~~~~~~~~~~~~~
 450
 451 Note that the two pairs of coordinates are not exactly the coordinates of the
 452 two fingers, but only the pair of the lower-left and upper-right coordinates.
 453 So the actual fingers might be situated on the other diagonal of the square
 454 defined by these two points.
 455
 456 byte 0:
 457
 458    bit   7   6   5   4   3   2   1   0
 459         n1  n0  ay8 ax8  .   .   R   L
 460
 461          L, R = 1 when Left, Right mouse button pressed
 462          n1..n0 = number of fingers on touchpad
 463
 464 byte 1:
 465
 466    bit   7   6   5   4   3   2   1   0
 467         ax7 ax6 ax5 ax4 ax3 ax2 ax1 ax0
 468
 469          ax8..ax0 = lower-left finger absolute x value
 470
 471 byte 2:
 472
 473    bit   7   6   5   4   3   2   1   0
 474         ay7 ay6 ay5 ay4 ay3 ay2 ay1 ay0
 475
 476          ay8..ay0 = lower-left finger absolute y value
 477
 478 byte 3:
 479
 480    bit   7   6   5   4   3   2   1   0
 481          .   .  by8 bx8  .   .   .   .
 482
 483 byte 4:
 484
 485    bit   7   6   5   4   3   2   1   0
 486         bx7 bx6 bx5 bx4 bx3 bx2 bx1 bx0
 487
 488          bx8..bx0 = upper-right finger absolute x value
 489
 490 byte 5:
 491
 492    bit   7   6   5   4   3   2   1   0
 493         by7 by8 by5 by4 by3 by2 by1 by0
 494
 495          by8..by0 = upper-right finger absolute y value
 496
 497 /////////////////////////////////////////////////////////////////////////////
 498
 499 6. Hardware version 3
 500    ==================
 501
 502 6.1 Registers
 503     ~~~~~~~~~
 504 * reg_10
 505
 506    bit   7   6   5   4   3   2   1   0
 507          0   0   0   0   R   F   T   A
 508
 509          A: 1 = enable absolute tracking
 510          T: 1 = enable two finger mode auto correct
 511          F: 1 = disable ABS Position Filter
 512          R: 1 = enable real hardware resolution
 513
 514 6.2 Native absolute mode 6 byte packet format
 515     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 516 1 and 3 finger touch shares the same 6-byte packet format, except that
 517 3 finger touch only reports the position of the center of all three fingers.
 518
 519 Firmware would send 12 bytes of data for 2 finger touch.
 520
 521 Note on debounce:
 522 In case the box has unstable power supply or other electricity issues, or
 523 when number of finger changes, F/W would send "debounce packet" to inform
 524 driver that the hardware is in debounce status.
 525 The debouce packet has the following signature:
 526     byte 0: 0xc4
 527     byte 1: 0xff
 528     byte 2: 0xff
 529     byte 3: 0x02
 530     byte 4: 0xff
 531     byte 5: 0xff
 532 When we encounter this kind of packet, we just ignore it.
 533
 534 6.2.1 One/Three finger touch
 535       ~~~~~~~~~~~~~~~~~~~~~~
 536
 537 byte 0:
 538
 539    bit   7   6   5   4   3   2   1   0
 540         n1  n0  w3  w2   0   1   R   L
 541
 542         L, R = 1 when Left, Right mouse button pressed
 543         n1..n0 = number of fingers on touchpad
 544
 545 byte 1:
 546
 547    bit   7   6   5   4   3   2   1   0
 548         p7  p6  p5  p4 x11 x10  x9  x8
 549
 550 byte 2:
 551
 552    bit   7   6   5   4   3   2   1   0
 553         x7  x6  x5  x4  x3  x2  x1  x0
 554
 555         x11..x0 = absolute x value (horizontal)
 556
 557 byte 3:
 558
 559    bit   7   6   5   4   3   2   1   0
 560          0   0  w1  w0   0   0   1   0
 561
 562          w3..w0 = width of the finger touch
 563
 564 byte 4:
 565
 566    bit   7   6   5   4   3   2   1   0
 567         p3  p1  p2  p0  y11 y10 y9  y8
 568
 569         p7..p0 = pressure
 570
 571 byte 5:
 572
 573    bit   7   6   5   4   3   2   1   0
 574         y7  y6  y5  y4  y3  y2  y1  y0
 575
 576         y11..y0 = absolute y value (vertical)
 577
 578 6.2.2 Two finger touch
 579       ~~~~~~~~~~~~~~~~
 580
 581 The packet format is exactly the same for two finger touch, except the hardware
 582 sends two 6 byte packets. The first packet contains data for the first finger,
 583 the second packet has data for the second finger. So for two finger touch a
 584 total of 12 bytes are sent.
 585
 586 /////////////////////////////////////////////////////////////////////////////
 587
 588 7. Hardware version 4
 589    ==================
 590
 591 7.1 Registers
 592     ~~~~~~~~~
 593 * reg_07
 594
 595    bit   7   6   5   4   3   2   1   0
 596          0   0   0   0   0   0   0   A
 597
 598          A: 1 = enable absolute tracking
 599
 600 7.2 Native absolute mode 6 byte packet format
 601     ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 602 v4 hardware is a true multitouch touchpad, capable of tracking up to 5 fingers.
 603 Unfortunately, due to PS/2's limited bandwidth, its packet format is rather
 604 complex.
 605
 606 Whenever the numbers or identities of the fingers changes, the hardware sends a
 607 status packet to indicate how many and which fingers is on touchpad, followed by
 608 head packets or motion packets. A head packet contains data of finger id, finger
 609 position (absolute x, y values), width, and pressure. A motion packet contains
 610 two fingers' position delta.
 611
 612 For example, when status packet tells there are 2 fingers on touchpad, then we
 613 can expect two following head packets. If the finger status doesn't change,
 614 the following packets would be motion packets, only sending delta of finger
 615 position, until we receive a status packet.
 616
 617 One exception is one finger touch. when a status packet tells us there is only
 618 one finger, the hardware would just send head packets afterwards.
 619
 620 7.2.1 Status packet
 621       ~~~~~~~~~~~~~
 622
 623 byte 0:
 624
 625    bit   7   6   5   4   3   2   1   0
 626          .   .   .   .   0   1   R   L
 627
 628          L, R = 1 when Left, Right mouse button pressed
 629
 630 byte 1:
 631
 632    bit   7   6   5   4   3   2   1   0
 633          .   .   . ft4 ft3 ft2 ft1 ft0
 634
 635          ft4 ft3 ft2 ft1 ft0 ftn = 1 when finger n is on touchpad
 636
 637 byte 2: not used
 638
 639 byte 3:
 640
 641    bit   7   6   5   4   3   2   1   0
 642          .   .   .   1   0   0   0   0
 643
 644          constant bits
 645
 646 byte 4:
 647
 648    bit   7   6   5   4   3   2   1   0
 649          p   .   .   .   .   .   .   .
 650
 651          p = 1 for palm
 652
 653 byte 5: not used
 654
 655 7.2.2 Head packet
 656       ~~~~~~~~~~~
 657
 658 byte 0:
 659
 660    bit   7   6   5   4   3   2   1   0
 661         w3  w2  w1  w0   0   1   R   L
 662
 663         L, R = 1 when Left, Right mouse button pressed
 664         w3..w0 = finger width (spans how many trace lines)
 665
 666 byte 1:
 667
 668    bit   7   6   5   4   3   2   1   0
 669         p7  p6  p5  p4 x11 x10  x9  x8
 670
 671 byte 2:
 672
 673    bit   7   6   5   4   3   2   1   0
 674         x7  x6  x5  x4  x3  x2  x1  x0
 675
 676         x11..x0 = absolute x value (horizontal)
 677
 678 byte 3:
 679
 680    bit   7   6   5   4   3   2   1   0
 681        id2 id1 id0   1   0   0   0   1
 682
 683        id2..id0 = finger id
 684
 685 byte 4:
 686
 687    bit   7   6   5   4   3   2   1   0
 688         p3  p1  p2  p0  y11 y10 y9  y8
 689
 690         p7..p0 = pressure
 691
 692 byte 5:
 693
 694    bit   7   6   5   4   3   2   1   0
 695         y7  y6  y5  y4  y3  y2  y1  y0
 696
 697         y11..y0 = absolute y value (vertical)
 698
 699 7.2.3 Motion packet
 700       ~~~~~~~~~~~~~
 701
 702 byte 0:
 703
 704    bit   7   6   5   4   3   2   1   0
 705        id2 id1 id0   w   0   1   R   L
 706
 707        L, R = 1 when Left, Right mouse button pressed
 708        id2..id0 = finger id
 709        w = 1 when delta overflows (> 127 or < -128), in this case
 710        firmware sends us (delta x / 5) and (delta y  / 5)
 711
 712 byte 1:
 713
 714    bit   7   6   5   4   3   2   1   0
 715         x7  x6  x5  x4  x3  x2  x1  x0
 716
 717         x7..x0 = delta x (two's complement)
 718
 719 byte 2:
 720
 721    bit   7   6   5   4   3   2   1   0
 722         y7  y6  y5  y4  y3  y2  y1  y0
 723
 724         y7..y0 = delta y (two's complement)
 725
 726 byte 3:
 727
 728    bit   7   6   5   4   3   2   1   0
 729        id2 id1 id0   1   0   0   1   0
 730
 731        id2..id0 = finger id
 732
 733 byte 4:
 734
 735    bit   7   6   5   4   3   2   1   0
 736         x7  x6  x5  x4  x3  x2  x1  x0
 737
 738         x7..x0 = delta x (two's complement)
 739
 740 byte 5:
 741
 742    bit   7   6   5   4   3   2   1   0
 743         y7  y6  y5  y4  y3  y2  y1  y0
 744
 745         y7..y0 = delta y (two's complement)
 746
 747         byte 0 ~ 2 for one finger
 748         byte 3 ~ 5 for another