search for: max_read_write

..., changing the call to usb_resetep did solve the problem for me, but the next problem was during reading of the data from the UPS - it constantly failed with the error "Invalid argument". It took quite some time to understand what the problem is, but finally it appeared that libusb uses MAX_READ_WRITE constant that is equal to 16*1024 as limiting value when reading from USB device, while my UPS has 8 bytes maximal packet size, and thus it seems that all readings must be done by blocks that are not larger than 8 bytes. When I set MAX_READ_WRITE to 8 and recompiled libusb, everything worked fine....