Attempting to write a device driver for the macbook's USB trackpad

[Vincent Hoffman]

Rohit Grover wrote:
> Hello People,
>
> I'm attempting to write a FreeBSD device driver for the USB trackpad on my
> macbook.
>   
Not much help but http://wiki.freebsd.org/AppleMacbook says or implies
that Rui Paulo was working on somthing similar under the touchpad
section, it might be worth talking to him directly
(http://wiki.freebsd.org/RuiPaulo .)
> The trackpad is an HID class device. Parsing the HID report descriptor
> (fetched from an invocation of usbd_read_report_desc()) for this device
> results in the following information:
>
> Legend: <descriptor_kind>: <page> <usage> <reportID>
>       <hid_location>
>
> input: page: 0x9; usage: 0x1; reportID: 2
>         size: 1, count: 1, loc: 0
> input: page: 0x9; usage: 0x2; reportID: 2
>         size: 1, count: 1, loc: 1
> input: page: 0x9; usage: 0x3; reportID: 2
>         size: 1, count: 1, loc: 2
> input: page: 0x0; usage: 0x0; reportID: 2
>         size: 5, count: 1, loc: 3
> input: page: 0x1; usage: 0x30; reportID: 2
>         size: 8, count: 1, loc: 8
> input: page: 0x1; usage: 0x31; reportID: 2
>         size: 8, count: 1, loc: 16
> input: page: 0xffff; usage: 0x2; reportID: 5
>         size: 8, count: 63, loc: 24
> collection: page: 0x1; usage: 0x2; collection: 1; collevel: 1, reportID: 0
>         size: 0, count: 0, loc: 0
> collection: page: 0x1; usage: 0x1; collection: 0; collevel: 2, reportID: 0
>         size: 0, count: 0, loc: 0
> collection: page: 0xffff; usage: 0x1; collection: 0; collevel: 1, reportID:
> 2
>         size: 8, count: 2, loc: 0
> feature: page: 0xffff; usage: 0x4, reportID: 5
>         size: 8, count: 1, loc: 0
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 8
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 16
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 24
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 32
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 40
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 48
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 56
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 64
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 72
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 80
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 88
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 96
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 104
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 112
> feature: page: 0x0; usage: 0x0, reportID: 5
>         size: 8, count: 1, loc: 120
> end_collection: page: 0x1; usage: 0x31, reportID: 2
>         size: 8, count: 2, loc: 0
> end_collection: page: 0x0; usage: 0x0, reportID: 2
>         size: 8, count: 2, loc: 0
> end_collection: page: 0xffff; usage: 0x4, reportID: 5
>         size: 8, count: 16, loc: 0
>
> As can be seen, there are two distinct report IDs being used. Report ID 2
> describes the mouse-buttons and XY deltas; and since the generic UMS driver
> in Freebsd is able to parse these values, the macbook's trackpad is usable.
> I would like to enhance the ums driver to report information from the
> pressure sensors--with the hope that this will allow the detection of tap
> events.
> I suspect that the reports with ID == 5 will contain this information. Of
> particular interest to me is the following (from the previous table):
>
> input: page: 0xffff; usage: 0x2; reportID: 5
>         size: 8, count: 63, loc: 24
>
> Unfortunately, this report uses a vendor specific page (0xffff), and
> therefore will require some reverse engineering before it can be deciphered.
>
> I need help with receiving HID reports for both ID == 2 and ID == 5.
> Currently, the interrupt handler (ums_intr) only parses reports with ID==2.
> Based on my reading of the code, ums_attach() needs to setup sc->sc_iid and
> sc->sc_isize based on the report-descriptors fetched from the device; but in
> the case where there are multiple reportIDs supported by the device, the
> current setup code uses values from only the first reportID.
>
> In order to parse reportID 2, sc->sc_isize is set to a value of 4 bytes: 1
> byte for the reportID header, together with 3 bytes for the button/XY-delta
> values.
> To accommodate an additional 63 bytes for the input in reportID 5, I am
> guessing that I should set sc->sc_isize to 68:  for the 63 bytes starting at
> bit offset 24; with allowance for one additional byte which may be necessary
> to accommodate a reportID header. I still don't know how to initialize
> sc->sc_iid to handle both report IDs.
>
> Can someone please help me with setting up the device to receive reports
> with both IDs so that I can begin reverse-engineering the vendor-specific
> content of reportID 5?
>
> regards,
> Rohit.
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