I know that thurrent documentation has been there since it was created by Alan Ott many years ago. And he started the HIDAPI project around that time as well. However, I am starting to doubt whether it is correct or not based on the testing using HIDAPI. Please help to clarify. Thanks. https://docs.kernel.org/hid/hidraw.html +++++++++++++++++++++++++++++++++++++++++++++++++++++ HIDIOCGFEATURE(len): Get a Feature Report This ioctl will request a feature report from the device using the control endpoint. The first byte of the supplied buffer should be set to the report number of the requested report. For devices which do not use numbered reports, set the first byte to 0. The returned report buffer will contain the report number in the first byte, followed by the report data read from the device. For devices which do not use numbered reports, the report data will begin at the first byte of the returned buffer. ++++++++++++++++++++++++++++++++++++++++++++++++++++++ I have doubts about the last sentence. It seems to me that for devices which do not use numbered reports, the first byte will be 0 and the report data begins in the second byte. This is based on testing results using hidapi and hidapitester, which use the ioctl. int HID_API_EXPORT hid_get_feature_report(hid_device *dev, unsigned char *data, size_t length) { int res; register_device_error(dev, NULL); res = ioctl(dev->device_handle, HIDIOCGFEATURE(length), data); if (res < 0) register_device_error_format(dev, "ioctl (GFEATURE): %s", strerror(errno)); return res; } Reference discussion: https://github.com/libusb/hidapi/issues/589 Test device is Jan Axelson's generic HID example which I have tested using libusb and hidapi across platforms as well as using Windows HID API. So I believe the FW is good. http://janaxelson.com/hidpage.htm#MyExampleCode (USB PIC MCU) -- Xiaofan
