ALPS Touchpad Protocol
Introduction
Currently the ALPS touchpad driver supports five protocol versions in use by
ALPS touchpads, called versions 1, 2, 3, 4 and 5.
Since roughly mid-2010 several new ALPS touchpads have been released and
integrated into a variety of laptops and netbooks. These new touchpads
have enough behavior differences that the alps_model_data definition
table, describing the properties of the different versions, is no longer
adequate. The design choices were to re-define the alps_model_data
table, with the risk of regression testing existing devices, or isolate
the new devices outside of the alps_model_data table. The latter design
choice was made. The new touchpad signatures are named: “Rushmore”,
“Pinnacle”, and “Dolphin”, which you will see in the alps.c code.
For the purposes of this document, this group of ALPS touchpads will
generically be called “new ALPS touchpads”.
We experimented with probing the ACPI interface _HID (Hardware ID)/_CID
(Compatibility ID) definition as a way to uniquely identify the
different ALPS variants but there did not appear to be a 1:1 mapping.
In fact, it appeared to be an m:n mapping between the _HID and actual
hardware type.
Detection
All ALPS touchpads should respond to the “E6 report” command sequence:
E8-E6-E6-E6-E9. An ALPS touchpad should respond with either 00-00-0A or
00-00-64 if no buttons are pressed. The bits 0-2 of the first byte will be 1s
if some buttons are pressed.
If the E6 report is successful, the touchpad model is identified using the “E7
report” sequence: E8-E7-E7-E7-E9. The response is the model signature and is
matched against known models in the alps_model_data_array.
For older touchpads supporting protocol versions 3 and 4, the E7 report
model signature is always 73-02-64. To differentiate between these
versions, the response from the “Enter Command Mode” sequence must be
inspected as described below.
The new ALPS touchpads have an E7 signature of 73-03-50 or 73-03-0A but
seem to be better differentiated by the EC Command Mode response.
Command Mode
Protocol versions 3 and 4 have a command mode that is used to read and write
one-byte device registers in a 16-bit address space. The command sequence
EC-EC-EC-E9 places the device in command mode, and the device will respond
with 88-07 followed by a third byte. This third byte can be used to determine
whether the devices uses the version 3 or 4 protocol.
To exit command mode, PSMOUSE_CMD_SETSTREAM (EA) is sent to the touchpad.
While in command mode, register addresses can be set by first sending a
specific command, either EC for v3 devices or F5 for v4 devices. Then the
address is sent one nibble at a time, where each nibble is encoded as a
command with optional data. This enoding differs slightly between the v3 and
v4 protocols.
Once an address has been set, the addressed register can be read by sending
PSMOUSE_CMD_GETINFO (E9). The first two bytes of the response contains the
address of the register being read, and the third contains the value of the
register. Registers are written by writing the value one nibble at a time
using the same encoding used for addresses.
For the new ALPS touchpads, the EC command is used to enter command
mode. The response in the new ALPS touchpads is significantly different,
and more important in determining the behavior. This code has been
separated from the original alps_model_data table and put in the
alps_identify function. For example, there seem to be two hardware init
sequences for the “Dolphin” touchpads as determined by the second byte
of the EC response.
Packet Format
In the following tables, the following notation is used.
CAPITALS = stick, miniscules = touchpad
?’s can have different meanings on different models, such as wheel rotation,
extra buttons, stick buttons on a dualpoint, etc.
PS/2 packet format
byte 0: 0 0 YSGN XSGN 1 M R L
byte 1: X7 X6 X5 X4 X3 X2 X1 X0
byte 2: Y7 Y6 Y5 Y4 Y3 Y2 Y1 Y0
Note that the device never signals overflow condition.
ALPS Absolute Mode - Protocol Verion 1
byte 0: 1 0 0 0 1 x9 x8 x7
byte 1: 0 x6 x5 x4 x3 x2 x1 x0
byte 2: 0 ? ? l r ? fin ges
byte 3: 0 ? ? ? ? y9 y8 y7
byte 4: 0 y6 y5 y4 y3 y2 y1 y0
byte 5: 0 z6 z5 z4 z3 z2 z1 z0
ALPS Absolute Mode - Protocol Version 2
byte 0: 1 ? ? ? 1 ? ? ?
byte 1: 0 x6 x5 x4 x3 x2 x1 x0
byte 2: 0 x10 x9 x8 x7 ? fin ges
byte 3: 0 y9 y8 y7 1 M R L
byte 4: 0 y6 y5 y4 y3 y2 y1 y0
byte 5: 0 z6 z5 z4 z3 z2 z1 z0
Dualpoint device – interleaved packet format
byte 0: 1 1 0 0 1 1 1 1
byte 1: 0 x6 x5 x4 x3 x2 x1 x0
byte 2: 0 x10 x9 x8 x7 0 fin ges
byte 3: 0 0 YSGN XSGN 1 1 1 1
byte 4: X7 X6 X5 X4 X3 X2 X1 X0
byte 5: Y7 Y6 Y5 Y4 Y3 Y2 Y1 Y0
byte 6: 0 y9 y8 y7 1 m r l
byte 7: 0 y6 y5 y4 y3 y2 y1 y0
byte 8: 0 z6 z5 z4 z3 z2 z1 z0
ALPS Absolute Mode - Protocol Version 3
ALPS protocol version 3 has three different packet formats. The first two are
associated with touchpad events, and the third is associatd with trackstick
events.
The first type is the touchpad position packet.
byte 0: 1 ? x1 x0 1 1 1 1
byte 1: 0 x10 x9 x8 x7 x6 x5 x4
byte 2: 0 y10 y9 y8 y7 y6 y5 y4
byte 3: 0 M R L 1 m r l
byte 4: 0 mt x3 x2 y3 y2 y1 y0
byte 5: 0 z6 z5 z4 z3 z2 z1 z0
Note that for some devices the trackstick buttons are reported in this packet,
and on others it is reported in the trackstick packets.
The second packet type contains bitmaps representing the x and y axes. In the
bitmaps a given bit is set if there is a finger covering that position on the
given axis. Thus the bitmap packet can be used for low-resolution multi-touch
data, although finger tracking is not possible. This packet also encodes the
number of contacts (f1 and f0 in the table below).
byte 0: 1 1 x1 x0 1 1 1 1
byte 1: 0 x8 x7 x6 x5 x4 x3 x2
byte 2: 0 y7 y6 y5 y4 y3 y2 y1
byte 3: 0 y10 y9 y8 1 1 1 1
byte 4: 0 x14 x13 x12 x11 x10 x9 y0
byte 5: 0 1 ? ? ? ? f1 f0
This packet only appears after a position packet with the mt bit set, and
usually only appears when there are two or more contacts (although
occasionally it’s seen with only a single contact).
The final v3 packet type is the trackstick packet.
byte 0: 1 1 x7 y7 1 1 1 1
byte 1: 0 x6 x5 x4 x3 x2 x1 x0
byte 2: 0 y6 y5 y4 y3 y2 y1 y0
byte 3: 0 1 0 0 1 0 0 0
byte 4: 0 z4 z3 z2 z1 z0 ? ?
byte 5: 0 0 1 1 1 1 1 1
ALPS Absolute Mode - Protocol Version 4
Protocol version 4 has an 8-byte packet format.
byte 0: 1 ? x1 x0 1 1 1 1
byte 1: 0 x10 x9 x8 x7 x6 x5 x4
byte 2: 0 y10 y9 y8 y7 y6 y5 y4
byte 3: 0 1 x3 x2 y3 y2 y1 y0
byte 4: 0 ? ? ? 1 ? r l
byte 5: 0 z6 z5 z4 z3 z2 z1 z0
byte 6: bitmap data (described below)
byte 7: bitmap data (described below)
The last two bytes represent a partial bitmap packet, with 3 full packets
required to construct a complete bitmap packet. Once assembled, the 6-byte
bitmap packet has the following format:
byte 0: 0 1 x7 x6 x5 x4 x3 x2
byte 1: 0 x1 x0 y4 y3 y2 y1 y0
byte 2: 0 0 ? x14 x13 x12 x11 x10
byte 3: 0 x9 x8 y9 y8 y7 y6 y5
byte 4: 0 0 0 0 0 0 0 0
byte 5: 0 0 0 0 0 0 0 y10
There are several things worth noting here.
In the bitmap data, bit 6 of byte 0 serves as a sync byte to
identify the first fragment of a bitmap packet.The bitmaps represent the same data as in the v3 bitmap packets, although
the packet layout is different.There doesn’t seem to be a count of the contact points anywhere in the v4
protocol packets. Deriving a count of contact points must be done by
analyzing the bitmaps.There is a 3 to 1 ratio of position packets to bitmap packets. Therefore
MT position can only be updated for every third ST position update, and
the count of contact points can only be updated every third packet as
well.
So far no v4 devices with tracksticks have been encountered.
ALPS Absolute Mode - Protocol Version 5
This is basically Protocol Version 3 but with different logic for packet
decode. It uses the same alps_process_touchpad_packet_v3 call with a
specialized decode_fields function pointer to correctly interpret the
packets. This appears to only be used by the Dolphin devices.
For single-touch, the 6-byte packet format is:
byte 0: 1 1 0 0 1 0 0 0
byte 1: 0 x6 x5 x4 x3 x2 x1 x0
byte 2: 0 y6 y5 y4 y3 y2 y1 y0
byte 3: 0 M R L 1 m r l
byte 4: y10 y9 y8 y7 x10 x9 x8 x7
byte 5: 0 z6 z5 z4 z3 z2 z1 z0
For mt, the format is:
byte 0: 1 1 1 n3 1 n2 n1 x24
byte 1: 1 y7 y6 y5 y4 y3 y2 y1
byte 2: ? x2 x1 y12 y11 y10 y9 y8
byte 3: 0 x23 x22 x21 x20 x19 x18 x17
byte 4: 0 x9 x8 x7 x6 x5 x4 x3
byte 5: 0 x16 x15 x14 x13 x12 x11 x10
