linux/Documentation/input/alps.txt
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   1ALPS Touchpad Protocol
   2----------------------
   3
   4Introduction
   5------------
   6
   7Currently the ALPS touchpad driver supports four protocol versions in use by
   8ALPS touchpads, called versions 1, 2, 3, and 4. Information about the various
   9protocol versions is contained in the following sections.
  10
  11Detection
  12---------
  13
  14All ALPS touchpads should respond to the "E6 report" command sequence:
  15E8-E6-E6-E6-E9. An ALPS touchpad should respond with either 00-00-0A or
  1600-00-64 if no buttons are pressed. The bits 0-2 of the first byte will be 1s
  17if some buttons are pressed.
  18
  19If the E6 report is successful, the touchpad model is identified using the "E7
  20report" sequence: E8-E7-E7-E7-E9. The response is the model signature and is
  21matched against known models in the alps_model_data_array.
  22
  23With protocol versions 3 and 4, the E7 report model signature is always
  2473-02-64. To differentiate between these versions, the response from the
  25"Enter Command Mode" sequence must be inspected as described below.
  26
  27Command Mode
  28------------
  29
  30Protocol versions 3 and 4 have a command mode that is used to read and write
  31one-byte device registers in a 16-bit address space. The command sequence
  32EC-EC-EC-E9 places the device in command mode, and the device will respond
  33with 88-07 followed by a third byte. This third byte can be used to determine
  34whether the devices uses the version 3 or 4 protocol.
  35
  36To exit command mode, PSMOUSE_CMD_SETSTREAM (EA) is sent to the touchpad.
  37
  38While in command mode, register addresses can be set by first sending a
  39specific command, either EC for v3 devices or F5 for v4 devices. Then the
  40address is sent one nibble at a time, where each nibble is encoded as a
  41command with optional data. This enoding differs slightly between the v3 and
  42v4 protocols.
  43
  44Once an address has been set, the addressed register can be read by sending
  45PSMOUSE_CMD_GETINFO (E9). The first two bytes of the response contains the
  46address of the register being read, and the third contains the value of the
  47register. Registers are written by writing the value one nibble at a time
  48using the same encoding used for addresses.
  49
  50Packet Format
  51-------------
  52
  53In the following tables, the following notation is used.
  54
  55 CAPITALS = stick, miniscules = touchpad
  56
  57?'s can have different meanings on different models, such as wheel rotation,
  58extra buttons, stick buttons on a dualpoint, etc.
  59
  60PS/2 packet format
  61------------------
  62
  63 byte 0:  0    0 YSGN XSGN    1    M    R    L
  64 byte 1: X7   X6   X5   X4   X3   X2   X1   X0
  65 byte 2: Y7   Y6   Y5   Y4   Y3   Y2   Y1   Y0
  66
  67Note that the device never signals overflow condition.
  68
  69ALPS Absolute Mode - Protocol Verion 1
  70--------------------------------------
  71
  72 byte 0:  1    0    0    0    1   x9   x8   x7
  73 byte 1:  0   x6   x5   x4   x3   x2   x1   x0
  74 byte 2:  0    ?    ?    l    r    ?  fin  ges
  75 byte 3:  0    ?    ?    ?    ?   y9   y8   y7
  76 byte 4:  0   y6   y5   y4   y3   y2   y1   y0
  77 byte 5:  0   z6   z5   z4   z3   z2   z1   z0
  78
  79ALPS Absolute Mode - Protocol Version 2
  80---------------------------------------
  81
  82 byte 0:  1    ?    ?    ?    1    ?    ?    ?
  83 byte 1:  0   x6   x5   x4   x3   x2   x1   x0
  84 byte 2:  0  x10   x9   x8   x7    ?  fin  ges
  85 byte 3:  0   y9   y8   y7    1    M    R    L
  86 byte 4:  0   y6   y5   y4   y3   y2   y1   y0
  87 byte 5:  0   z6   z5   z4   z3   z2   z1   z0
  88
  89Dualpoint device -- interleaved packet format
  90---------------------------------------------
  91
  92 byte 0:    1    1    0    0    1    1    1    1
  93 byte 1:    0   x6   x5   x4   x3   x2   x1   x0
  94 byte 2:    0  x10   x9   x8   x7    0  fin  ges
  95 byte 3:    0    0 YSGN XSGN    1    1    1    1
  96 byte 4:   X7   X6   X5   X4   X3   X2   X1   X0
  97 byte 5:   Y7   Y6   Y5   Y4   Y3   Y2   Y1   Y0
  98 byte 6:    0   y9   y8   y7    1    m    r    l
  99 byte 7:    0   y6   y5   y4   y3   y2   y1   y0
 100 byte 8:    0   z6   z5   z4   z3   z2   z1   z0
 101
 102ALPS Absolute Mode - Protocol Version 3
 103---------------------------------------
 104
 105ALPS protocol version 3 has three different packet formats. The first two are
 106associated with touchpad events, and the third is associatd with trackstick
 107events.
 108
 109The first type is the touchpad position packet.
 110
 111 byte 0:    1    ?   x1   x0    1    1    1    1
 112 byte 1:    0  x10   x9   x8   x7   x6   x5   x4
 113 byte 2:    0  y10   y9   y8   y7   y6   y5   y4
 114 byte 3:    0    M    R    L    1    m    r    l
 115 byte 4:    0   mt   x3   x2   y3   y2   y1   y0
 116 byte 5:    0   z6   z5   z4   z3   z2   z1   z0
 117
 118Note that for some devices the trackstick buttons are reported in this packet,
 119and on others it is reported in the trackstick packets.
 120
 121The second packet type contains bitmaps representing the x and y axes. In the
 122bitmaps a given bit is set if there is a finger covering that position on the
 123given axis. Thus the bitmap packet can be used for low-resolution multi-touch
 124data, although finger tracking is not possible.  This packet also encodes the
 125number of contacts (f1 and f0 in the table below).
 126
 127 byte 0:    1    1   x1   x0    1    1    1    1
 128 byte 1:    0   x8   x7   x6   x5   x4   x3   x2
 129 byte 2:    0   y7   y6   y5   y4   y3   y2   y1
 130 byte 3:    0  y10   y9   y8    1    1    1    1
 131 byte 4:    0  x14  x13  x12  x11  x10   x9   y0
 132 byte 5:    0    1    ?    ?    ?    ?   f1   f0
 133
 134This packet only appears after a position packet with the mt bit set, and
 135usually only appears when there are two or more contacts (although
 136occassionally it's seen with only a single contact).
 137
 138The final v3 packet type is the trackstick packet.
 139
 140 byte 0:    1    1   x7   y7    1    1    1    1
 141 byte 1:    0   x6   x5   x4   x3   x2   x1   x0
 142 byte 2:    0   y6   y5   y4   y3   y2   y1   y0
 143 byte 3:    0    1    0    0    1    0    0    0
 144 byte 4:    0   z4   z3   z2   z1   z0    ?    ?
 145 byte 5:    0    0    1    1    1    1    1    1
 146
 147ALPS Absolute Mode - Protocol Version 4
 148---------------------------------------
 149
 150Protocol version 4 has an 8-byte packet format.
 151
 152 byte 0:    1    ?   x1   x0    1    1    1    1
 153 byte 1:    0  x10   x9   x8   x7   x6   x5   x4
 154 byte 2:    0  y10   y9   y8   y7   y6   y5   y4
 155 byte 3:    0    1   x3   x2   y3   y2   y1   y0
 156 byte 4:    0    ?    ?    ?    1    ?    r    l
 157 byte 5:    0   z6   z5   z4   z3   z2   z1   z0
 158 byte 6:    bitmap data (described below)
 159 byte 7:    bitmap data (described below)
 160
 161The last two bytes represent a partial bitmap packet, with 3 full packets
 162required to construct a complete bitmap packet.  Once assembled, the 6-byte
 163bitmap packet has the following format:
 164
 165 byte 0:    0    1   x7   x6   x5   x4   x3   x2
 166 byte 1:    0   x1   x0   y4   y3   y2   y1   y0
 167 byte 2:    0    0    ?  x14  x13  x12  x11  x10
 168 byte 3:    0   x9   x8   y9   y8   y7   y6   y5
 169 byte 4:    0    0    0    0    0    0    0    0
 170 byte 5:    0    0    0    0    0    0    0  y10
 171
 172There are several things worth noting here.
 173
 174 1) In the bitmap data, bit 6 of byte 0 serves as a sync byte to
 175    identify the first fragment of a bitmap packet.
 176
 177 2) The bitmaps represent the same data as in the v3 bitmap packets, although
 178    the packet layout is different.
 179
 180 3) There doesn't seem to be a count of the contact points anywhere in the v4
 181    protocol packets. Deriving a count of contact points must be done by
 182    analyzing the bitmaps.
 183
 184 4) There is a 3 to 1 ratio of position packets to bitmap packets. Therefore
 185    MT position can only be updated for every third ST position update, and
 186    the count of contact points can only be updated every third packet as
 187    well.
 188
 189So far no v4 devices with tracksticks have been encountered.
 190
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