On Jun 28, 2009, at 11:28 PM, Steve Hawkins wrote:
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, and have attempted to
use the guidelines provided in the code for reading and writing to
our device. So far, I have not been to successfully read or write
to the device, and I suspect the reason may be that the report
descriptor for our devices specifies a 64 byte array for both the
input and output data reports.
Do you have some example code, and the resulting error codes from
reading/writing?
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. We
have verified that the device works in Windows, so I believe my
problem is on the Linux side. I read in another posting that the
MGE parser has problems parsing arrays, and I’m wondering if this
may be where my problems lie.
The parser has more problems with printing the arrays than with
parsing, but if you pass in the usage code for the first array
element, things should sort of work.
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
Can anyone provide some guidance on how to specify he HID path for
the following report descriptor (generated from lsusb –vvv):
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)
Looks like the path should be { 0xff000001, 0xff000001 }
Also, if you have something that effectively only sends one or two
requests (in your case, you only have one array per direction), it may
be easier to use usbsnoopy and convert one of those traces to raw
libusb calls. It's not as clean, but it should get the job done.
The "value add" for libhid is when you have a number of different
report IDs, each using a standard set of usages defined by a device
class.
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