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