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