summaryrefslogtreecommitdiffstats
path: root/Documentation/input/elantech.txt
blob: e1ae127ed099d4934e1d7fb95f1a8ba819c1da9b (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
Elantech Touchpad Driver
========================

	Copyright (C) 2007-2008 Arjan Opmeer <arjan@opmeer.net>

	Extra information for hardware version 1 found and
	provided by Steve Havelka

	Version 2 (EeePC) hardware support based on patches
	received from Woody at Xandros and forwarded to me
	by user StewieGriffin at the eeeuser.com forum


Contents
~~~~~~~~

 1. Introduction
 2. Extra knobs
 3. Differentiating hardware versions
 4. Hardware version 1
    4.1 Registers
    4.2 Native relative mode 4 byte packet format
    4.3 Native absolute mode 4 byte packet format
 5. Hardware version 2
    5.1 Registers
    5.2 Native absolute mode 6 byte packet format
        5.2.1 Parity checking and packet re-synchronization
        5.2.2 One/Three finger touch
        5.2.3 Two finger touch
 6. Hardware version 3
    6.1 Registers
    6.2 Native absolute mode 6 byte packet format
        6.2.1 One/Three finger touch
        6.2.2 Two finger touch
 7. Hardware version 4
    7.1 Registers
    7.2 Native absolute mode 6 byte packet format
        7.2.1 Status packet
        7.2.2 Head packet
        7.2.3 Motion packet



1. Introduction
   ~~~~~~~~~~~~

Currently the Linux Elantech touchpad driver is aware of two different
hardware versions unimaginatively called version 1 and version 2. Version 1
is found in "older" laptops and uses 4 bytes per packet. Version 2 seems to
be introduced with the EeePC and uses 6 bytes per packet, and provides
additional features such as position of two fingers, and width of the touch.

The driver tries to support both hardware versions and should be compatible
with the Xorg Synaptics touchpad driver and its graphical configuration
utilities.

Additionally the operation of the touchpad can be altered by adjusting the
contents of some of its internal registers. These registers are represented
by the driver as sysfs entries under /sys/bus/serio/drivers/psmouse/serio?
that can be read from and written to.

Currently only the registers for hardware version 1 are somewhat understood.
Hardware version 2 seems to use some of the same registers but it is not
known whether the bits in the registers represent the same thing or might
have changed their meaning.

On top of that, some register settings have effect only when the touchpad is
in relative mode and not in absolute mode. As the Linux Elantech touchpad
driver always puts the hardware into absolute mode not all information
mentioned below can be used immediately. But because there is no freely
available Elantech documentation the information is provided here anyway for
completeness sake.


/////////////////////////////////////////////////////////////////////////////


2. Extra knobs
   ~~~~~~~~~~~

Currently the Linux Elantech touchpad driver provides two extra knobs under
/sys/bus/serio/drivers/psmouse/serio? for the user.

* debug

   Turn different levels of debugging ON or OFF.

   By echoing "0" to this file all debugging will be turned OFF.

   Currently a value of "1" will turn on some basic debugging and a value of
   "2" will turn on packet debugging. For hardware version 1 the default is
   OFF. For version 2 the default is "1".

   Turning packet debugging on will make the driver dump every packet
   received to the syslog before processing it. Be warned that this can
   generate quite a lot of data!

* paritycheck

   Turns parity checking ON or OFF.

   By echoing "0" to this file parity checking will be turned OFF. Any
   non-zero value will turn it ON. For hardware version 1 the default is ON.
   For version 2 the default it is OFF.

   Hardware version 1 provides basic data integrity verification by
   calculating a parity bit for the last 3 bytes of each packet. The driver
   can check these bits and reject any packet that appears corrupted. Using
   this knob you can bypass that check.

   Hardware version 2 does not provide the same parity bits. Only some basic
   data consistency checking can be done. For now checking is disabled by
   default. Currently even turning it on will do nothing.

/////////////////////////////////////////////////////////////////////////////

3. Differentiating hardware versions
   =================================

To detect the hardware version, read the version number as param[0].param[1].param[2]

 4 bytes version: (after the arrow is the name given in the Dell-provided driver)
 02.00.22 => EF013
 02.06.00 => EF019
In the wild, there appear to be more versions, such as 00.01.64, 01.00.21,
02.00.00, 02.00.04, 02.00.06.

 6 bytes:
 02.00.30 => EF113
 02.08.00 => EF023
 02.08.XX => EF123
 02.0B.00 => EF215
 04.01.XX => Scroll_EF051
 04.02.XX => EF051
In the wild, there appear to be more versions, such as 04.03.01, 04.04.11. There
appears to be almost no difference, except for EF113, which does not report
pressure/width and has different data consistency checks.

Probably all the versions with param[0] <= 01 can be considered as
4 bytes/firmware 1. The versions < 02.08.00, with the exception of 02.00.30, as
4 bytes/firmware 2. Everything >= 02.08.00 can be considered as 6 bytes.

/////////////////////////////////////////////////////////////////////////////

4. Hardware version 1
   ==================

4.1 Registers
    ~~~~~~~~~

By echoing a hexadecimal value to a register it contents can be altered.

For example:

   echo -n 0x16 > reg_10

* reg_10

   bit   7   6   5   4   3   2   1   0
         B   C   T   D   L   A   S   E

         E: 1 = enable smart edges unconditionally
         S: 1 = enable smart edges only when dragging
         A: 1 = absolute mode (needs 4 byte packets, see reg_11)
         L: 1 = enable drag lock (see reg_22)
         D: 1 = disable dynamic resolution
         T: 1 = disable tapping
         C: 1 = enable corner tap
         B: 1 = swap left and right button

* reg_11

   bit   7   6   5   4   3   2   1   0
         1   0   0   H   V   1   F   P

         P: 1 = enable parity checking for relative mode
         F: 1 = enable native 4 byte packet mode
         V: 1 = enable vertical scroll area
         H: 1 = enable horizontal scroll area

* reg_20

         single finger width?

* reg_21

         scroll area width (small: 0x40 ... wide: 0xff)

* reg_22

         drag lock time out (short: 0x14 ... long: 0xfe;
                             0xff = tap again to release)

* reg_23

         tap make timeout?

* reg_24

         tap release timeout?

* reg_25

         smart edge cursor speed (0x02 = slow, 0x03 = medium, 0x04 = fast)

* reg_26

         smart edge activation area width?


4.2 Native relative mode 4 byte packet format
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

byte 0:
   bit   7   6   5   4   3   2   1   0
         c   c  p2  p1   1   M   R   L

         L, R, M = 1 when Left, Right, Middle mouse button pressed
            some models have M as byte 3 odd parity bit
         when parity checking is enabled (reg_11, P = 1):
            p1..p2 = byte 1 and 2 odd parity bit
         c = 1 when corner tap detected

byte 1:
   bit   7   6   5   4   3   2   1   0
        dx7 dx6 dx5 dx4 dx3 dx2 dx1 dx0

         dx7..dx0 = x movement;   positive = right, negative = left
         byte 1 = 0xf0 when corner tap detected

byte 2:
   bit   7   6   5   4   3   2   1   0
        dy7 dy6 dy5 dy4 dy3 dy2 dy1 dy0

         dy7..dy0 = y movement;   positive = up,    negative = down

byte 3:
   parity checking enabled (reg_11, P = 1):

      bit   7   6   5   4   3   2   1   0
            w   h  n1  n0  ds3 ds2 ds1 ds0

            normally:
               ds3..ds0 = scroll wheel amount and direction
                          positive = down or left
                          negative = up or right
            when corner tap detected:
               ds0 = 1 when top right corner tapped
               ds1 = 1 when bottom right corner tapped
               ds2 = 1 when bottom left corner tapped
               ds3 = 1 when top left corner tapped
            n1..n0 = number of fingers on touchpad
               only models with firmware 2.x report this, models with
               firmware 1.x seem to map one, two and three finger taps
               directly to L, M and R mouse buttons
            h = 1 when horizontal scroll action
            w = 1 when wide finger touch?

   otherwise (reg_11, P = 0):

      bit   7   6   5   4   3   2   1   0
           ds7 ds6 ds5 ds4 ds3 ds2 ds1 ds0

            ds7..ds0 = vertical scroll amount and direction
                       negative = up
                       positive = down


4.3 Native absolute mode 4 byte packet format
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

EF013 and EF019 have a special behaviour (due to a bug in the firmware?), and
when 1 finger is touching, the first 2 position reports must be discarded.
This counting is reset whenever a different number of fingers is reported.

byte 0:
   firmware version 1.x:

      bit   7   6   5   4   3   2   1   0
            D   U  p1  p2   1  p3   R   L

            L, R = 1 when Left, Right mouse button pressed
            p1..p3 = byte 1..3 odd parity bit
            D, U = 1 when rocker switch pressed Up, Down

   firmware version 2.x:

      bit   7   6   5   4   3   2   1   0
           n1  n0  p2  p1   1  p3   R   L

            L, R = 1 when Left, Right mouse button pressed
            p1..p3 = byte 1..3 odd parity bit
            n1..n0 = number of fingers on touchpad

byte 1:
   firmware version 1.x:

      bit   7   6   5   4   3   2   1   0
            f   0  th  tw  x9  x8  y9  y8

            tw = 1 when two finger touch
            th = 1 when three finger touch
            f  = 1 when finger touch

   firmware version 2.x:

      bit   7   6   5   4   3   2   1   0
            .   .   .   .  x9  x8  y9  y8

byte 2:
   bit   7   6   5   4   3   2   1   0
        x7  x6  x5  x4  x3  x2  x1  x0

         x9..x0 = absolute x value (horizontal)

byte 3:
   bit   7   6   5   4   3   2   1   0
        y7  y6  y5  y4  y3  y2  y1  y0

         y9..y0 = absolute y value (vertical)


/////////////////////////////////////////////////////////////////////////////


5. Hardware version 2
   ==================


5.1 Registers
    ~~~~~~~~~

By echoing a hexadecimal value to a register it contents can be altered.

For example:

   echo -n 0x56 > reg_10

* reg_10

   bit   7   6   5   4   3   2   1   0
         0   1   0   1   0   1   D   0

         D: 1 = enable drag and drop

* reg_11

   bit   7   6   5   4   3   2   1   0
         1   0   0   0   S   0   1   0

         S: 1 = enable vertical scroll

* reg_21

         unknown (0x00)

* reg_22

         drag and drop release time out (short: 0x70 ... long 0x7e;
                                   0x7f = never i.e. tap again to release)


5.2 Native absolute mode 6 byte packet format
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
5.2.1 Parity checking and packet re-synchronization
There is no parity checking, however some consistency checks can be performed.

For instance for EF113:
        SA1= packet[0];
        A1 = packet[1];
        B1 = packet[2];
        SB1= packet[3];
        C1 = packet[4];
        D1 = packet[5];
        if( (((SA1 & 0x3C) != 0x3C) && ((SA1 & 0xC0) != 0x80)) || // check Byte 1
            (((SA1 & 0x0C) != 0x0C) && ((SA1 & 0xC0) == 0x80)) || // check Byte 1 (one finger pressed)
            (((SA1 & 0xC0) != 0x80) && (( A1 & 0xF0) != 0x00)) || // check Byte 2
            (((SB1 & 0x3E) != 0x38) && ((SA1 & 0xC0) != 0x80)) || // check Byte 4
            (((SB1 & 0x0E) != 0x08) && ((SA1 & 0xC0) == 0x80)) || // check Byte 4 (one finger pressed)
            (((SA1 & 0xC0) != 0x80) && (( C1 & 0xF0) != 0x00))  ) // check Byte 5
		// error detected

For all the other ones, there are just a few constant bits:
        if( ((packet[0] & 0x0C) != 0x04) ||
            ((packet[3] & 0x0f) != 0x02) )
		// error detected


In case an error is detected, all the packets are shifted by one (and packet[0] is discarded).

5.2.2 One/Three finger touch
      ~~~~~~~~~~~~~~~~

byte 0:

   bit   7   6   5   4   3   2   1   0
	 n1  n0  w3  w2   .   .   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
	 n4  vf  w1  w0   .   .   .  b2

	 n4 = set if more than 3 fingers (only in 3 fingers mode)
	 vf = a kind of flag ? (only on EF123, 0 when finger is over one
	      of the buttons, 1 otherwise)
	 w3..w0 = width of the finger touch (not EF113)
	 b2 (on EF113 only, 0 otherwise), b2.R.L indicates one button pressed:
		0 = none
		1 = Left
		2 = Right
		3 = Middle (Left and Right)
		4 = Forward
		5 = Back
		6 = Another one
		7 = Another one

byte 4:

   bit   7   6   5   4   3   2   1   0
        p3  p1  p2  p0  y11 y10 y9  y8

	 p7..p0 = pressure (not EF113)

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)


5.2.3 Two finger touch
      ~~~~~~~~~~~~~~~~

Note that the two pairs of coordinates are not exactly the coordinates of the
two fingers, but only the pair of the lower-left and upper-right coordinates.
So the actual fingers might be situated on the other diagonal of the square
defined by these two points.

byte 0:

   bit   7   6   5   4   3   2   1   0
        n1  n0  ay8 ax8  .   .   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
        ax7 ax6 ax5 ax4 ax3 ax2 ax1 ax0

	 ax8..ax0 = lower-left finger absolute x value

byte 2:

   bit   7   6   5   4   3   2   1   0
        ay7 ay6 ay5 ay4 ay3 ay2 ay1 ay0

	 ay8..ay0 = lower-left finger absolute y value

byte 3:

   bit   7   6   5   4   3   2   1   0
         .   .  by8 bx8  .   .   .   .

byte 4:

   bit   7   6   5   4   3   2   1   0
        bx7 bx6 bx5 bx4 bx3 bx2 bx1 bx0

         bx8..bx0 = upper-right finger absolute x value

byte 5:

   bit   7   6   5   4   3   2   1   0
        by7 by8 by5 by4 by3 by2 by1 by0

         by8..by0 = upper-right finger absolute y value

/////////////////////////////////////////////////////////////////////////////

6. Hardware version 3
   ==================

6.1 Registers
    ~~~~~~~~~
* reg_10

   bit   7   6   5   4   3   2   1   0
         0   0   0   0   R   F   T   A

         A: 1 = enable absolute tracking
         T: 1 = enable two finger mode auto correct
         F: 1 = disable ABS Position Filter
         R: 1 = enable real hardware resolution

6.2 Native absolute mode 6 byte packet format
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1 and 3 finger touch shares the same 6-byte packet format, except that
3 finger touch only reports the position of the center of all three fingers.

Firmware would send 12 bytes of data for 2 finger touch.

Note on debounce:
In case the box has unstable power supply or other electricity issues, or
when number of finger changes, F/W would send "debounce packet" to inform
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
OpenPOWER on IntegriCloud