Why isn the host polling my devices high-speed interrupt endpoint at the correct rate?
For low- and full-speed interrupt endpoints, the descriptor’s bInterval value indicates the requested maximum number of milliseconds between transaction attempts. For high-speed interrupt endpoints, the interval is calculated differently. According to the USB 2.0 specification, bInterval must be between 1 and 16, the interval is in units of 125 microseconds, and the interval’s value equals 2^(bInterval-1) (with ^ indicating the exponent operator). In other words, if bInterval = 4, the interval is 2^(4-1), or 2^3, or eight 125-microsecond periods, which means that the device is requesting a minimum of one poll per millisecond. Reports are that some device providers are using full-speed bInterval values in high-speed descriptors. Reports also say that under Windows, a device may receive its intended polling rate (rather than its requested polling rate) in spite of this error. Other operating systems are likely to attempt to provide the requested polling rate, or may report an illegal bIn
