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+ALPS Touchpad Protocol
+----------------------
+
+Introduction
+------------
+Currently the ALPS touchpad driver supports seven protocol versions in use by
+ALPS touchpads, called versions 1, 2, 3, 4, 5, 6 and 7.
+
+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 encoding 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.
+
+For protocol version 2 devices when the trackpoint is used, and no fingers
+are on the touchpad, the M R L bits signal the combined status of both the
+pointingstick and touchpad buttons.
+
+ALPS Absolute Mode - Protocol Version 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  PSM  PSR  PSL
+ 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
+
+Protocol Version 2 DualPoint devices send standard PS/2 mouse packets for
+the DualPoint Stick. For non interleaved dualpoint devices the pointingstick
+buttons get reported separately in the PSM, PSR and PSL bits.
+
+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
+
+Devices which use the interleaving format normally send standard PS/2 mouse
+packets for the DualPoint Stick + ALPS Absolute Mode packets for the
+touchpad, switching to the interleaved packet format when both the stick and
+the touchpad are used at the same time.
+
+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 associated 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.
+
+ 1) In the bitmap data, bit 6 of byte 0 serves as a sync byte to
+    identify the first fragment of a bitmap packet.
+
+ 2) The bitmaps represent the same data as in the v3 bitmap packets, although
+    the packet layout is different.
+
+ 3) 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.
+
+ 4) 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
+
+ALPS Absolute Mode - Protocol Version 6
+---------------------------------------
+
+For trackstick packet, the format is:
+
+ byte 0:    1    1    1    1    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:    ?   Y7   X7    ?    ?    M    R    L
+ byte 4:   Z7   Z6   Z5   Z4   Z3   Z2   Z1   Z0
+ byte 5:    0    1    1    1    1    1    1    1
+
+For touchpad packet, the format is:
+
+ byte 0:    1    1    1    1    1    1    1    1
+ byte 1:    0    0    0    0   x3   x2   x1   x0
+ byte 2:    0    0    0    0   y3   y2   y1   y0
+ byte 3:    ?   x7   x6   x5   x4    ?    r    l
+ byte 4:    ?   y7   y6   y5   y4    ?    ?    ?
+ byte 5:   z7   z6   z5   z4   z3   z2   z1   z0
+
+(v6 touchpad does not have middle button)
+
+ALPS Absolute Mode - Protocol Version 7
+---------------------------------------
+
+For trackstick packet, the format is:
+
+ byte 0:    0    1    0    0    1    0    0    0
+ byte 1:    1    1    *    *    1    M    R    L
+ byte 2:   X7    1   X5   X4   X3   X2   X1   X0
+ byte 3:   Z6    1   Y6   X6    1   Y2   Y1   Y0
+ byte 4:   Y7    0   Y5   Y4   Y3    1    1    0
+ byte 5:  T&P    0   Z5   Z4   Z3   Z2   Z1   Z0
+
+For touchpad packet, the format is:
+
+         packet-fmt     b7     b6     b5     b4     b3     b2     b1     b0
+ byte 0: TWO & MULTI     L      1      R      M      1   Y0-2   Y0-1   Y0-0
+ byte 0: NEW             L      1   X1-5      1      1   Y0-2   Y0-1   Y0-0
+ byte 1:             Y0-10   Y0-9   Y0-8   Y0-7   Y0-6   Y0-5   Y0-4   Y0-3
+ byte 2:             X0-11      1  X0-10   X0-9   X0-8   X0-7   X0-6   X0-5
+ byte 3:             X1-11      1   X0-4   X0-3      1   X0-2   X0-1   X0-0
+ byte 4: TWO         X1-10    TWO   X1-9   X1-8   X1-7   X1-6   X1-5   X1-4
+ byte 4: MULTI       X1-10    TWO   X1-9   X1-8   X1-7   X1-6   Y1-5      1
+ byte 4: NEW         X1-10    TWO   X1-9   X1-8   X1-7   X1-6      0      0
+ byte 5: TWO & NEW   Y1-10      0   Y1-9   Y1-8   Y1-7   Y1-6   Y1-5   Y1-4
+ byte 5: MULTI       Y1-10      0   Y1-9   Y1-8   Y1-7   Y1-6    F-1    F-0
+
+ L:         Left button
+ R / M:     Non-clickpads: Right / Middle button
+            Clickpads: When > 2 fingers are down, and some fingers
+            are in the button area, then the 2 coordinates reported
+            are for fingers outside the button area and these report
+            extra fingers being present in the right / left button
+            area. Note these fingers are not added to the F field!
+            so if a TWO packet is received and R = 1 then there are
+            3 fingers down, etc.
+ TWO:       1: Two touches present, byte 0/4/5 are in TWO fmt
+            0: If byte 4 bit 0 is 1, then byte 0/4/5 are in MULTI fmt
+               otherwise byte 0 bit 4 must be set and byte 0/4/5 are
+               in NEW fmt
+ F:         Number of fingers - 3, 0 means 3 fingers, 1 means 4 ...