Hi , Thanx for the reply . The below discussions clears the ambiguity regarding <report id > usage . I hope some patch regarding the same bug fix will be there for hidraw interface . Thanx & regards Amit Nagal On Tue, Jun 29, 2010 at 4:32 PM, Xiaofan Chen <xiaofanc@xxxxxxxxx> wrote: > On Wed, Jun 30, 2010 at 12:30 AM, Alan Ott <alan@xxxxxxxxxxx> wrote: > >> I thought I'd be able to just go check the HID specification and be able to >> say that the report number is not sent as part of the payload for Set_Report >> devices, since it would be redundant because the Report ID is sent over in >> the wValue field. >> >> Unfortunately, I was not able to see that clearly laid out in the HID >> specification in the section on Set_Report. I did however find language >> saying "if a Report ID tag was used in the Report descriptor, all reports >> include a single byte ID prefix," in section 8.1, Report Types. >> >> I did some tests with the Windows implementation, and indeed, when numbered >> reports are used in the HID descriptor, the Windows implementation will send >> the report ID as the first byte of the payload.>> >> Based on the language in the HID spec, and the behavior of Windows, I >> believe the buf+1, count-1 to be a bug. >> > > Yes I think it is a bug. > > And the HID specification states: > "If a Report ID tag was used in the Report descriptor, all reports > include a single byte ID prefix. If the Report ID tag was not used, all > values are returned in a single report and a prefix ID is not included > in that report." > > My understanding is like the following and testing confirms it. > 1) when HID device has explicit report IDs, then the report IDs will > be transmitted on the bus. > 2) when the HID device does not use report ID at all (implicit report ID 0), > then this report ID 0 is not transmitted on the bus > > Reference: > http://www.microchip.com/forums/tm.aspx?m=494711 > http://libusb.6.n5.nabble.com/Missing-first-byte-when-reading-HID-Feature-Reports-with-ID-td9460.html > (we spent quite some efforts to get the libusb-1.0 Windows native > HID backend to deal with report ID correctly). > > -- > Xiaofan http://sourceforge.net/projects/libusb-win32/ > -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
