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PODetermining the HID Path for USB HID device using libhid on Linux
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copied!<p>I’m interested in using libhid to access a custom HID device that we are developing on a PIC microcontroller. I have been able to successfully get the test_libhid code to run. The instructions for reading and writing to devices using this library are provided as comments in the test_libhid code.</p> <p>I have attempted to follow the documented techniques for reading and writing, but so far, I have not been to successfully read or write to the device. I suspect the reason may be that the report descriptor for the device specifies a 64 byte array for both the input and output data reports.</p> <p>I have read the details contained in the Device Class Definition for HID section from usb.org, and I think that I understand how descriptors work in general and how they translate to HID paths, but my attempts to read and write data to the device have failed. </p> <p>I have verified that the device works in Windows, so my problem appears to lie on the Linux side. I don’t think that it should matter, but I should note that I’m currently working in a VMWare virtual machine, loaded with Ubuntu 8.04 server</p> <p>Can anyone provide some guidance on how to specify he HID path for the following report descriptor (generated from lsusb –vvv):</p> <pre><code>Report Descriptor: (length is 29) Item(Global): Usage Page, data= [ 0x00 0xff ] 65280 (null) Item(Local ): Usage, data= [ 0x01 ] 1 (null) Item(Main ): Collection, data= [ 0x01 ] 1 Application Item(Local ): Usage Minimum, data= [ 0x01 ] 1 (null) Item(Local ): Usage Maximum, data= [ 0x40 ] 64 (null) Item(Global): Logical Minimum, data= [ 0x00 ] 0 Item(Global): Logical Maximum, data= [ 0xff 0x00 ] 255 Item(Global): Report Size, data= [ 0x08 ] 8 Item(Global): Report Count, data= [ 0x40 ] 64 Item(Main ): Input, data= [ 0x02 ] 2 Data Variable Absolute No_Wrap Linear Preferred_State No_Null_Position Non_Volatile Bitfield Item(Local ): Usage Minimum, data= [ 0x01 ] 1 (null) Item(Local ): Usage Maximum, data= [ 0x40 ] 64 (null) Item(Main ): Output, data= [ 0x02 ] 2 Data Variable Absolute No_Wrap Linear Preferred_State No_Null_Position Non_Volatile Bitfield Item(Main ): End Collection, data=none </code></pre> <p>Also, when I run the test_libhid program, it dumps the parse tree as 64 identical entries that look like this:</p> <pre><code>path: 0xff000001.0x00000000; type: 0x80 </code></pre> <p>These are presumably the inputs. This list is followed by another 64 entries that look like this:</p> <pre><code>path: 0xff000001.0x00000000; type: 0x90 </code></pre> <p>I have posted to the libhid mailing list, but there has not been much activity there recently, so I thought that I would bring my question here. If anyone can provide guidance on how the HID path for this input and output report should be specified, it would be a tremendous help.</p> <p>Thanks.</p>

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