Circuit and method for producing USB host working clock

A circuit for producing USB host working clock, comprising:

• an internal oscillator, a clock with a fixed frequency is produced by said internal oscillator;
• a controllable frequency divider, said controllable frequency divider is connected to said internal oscillator, and the clock that is produced by said internal oscillator is processed with a frequency division by said controllable frequency divider in a set frequency dividing ratio;
• a frequency multiplier, said frequency multiplier is connected to said controllable frequency divider, the clock is processed with the frequency division by said controllable frequency divider, which is processed with a frequency multiplication by said frequency multiplier in a fixed frequency multiplication ratio;
• a USB host interface, said USB host interface is connected to said frequency multiplier, said frequency multiplier transmits a frequency of the clock that is multiplied to said USB host interface, according to the clock that is provided by said frequency multiplier, said USB host interface configures with USB peripherals for responding;
• a frequency division controller, said frequency division controller is connected to said USB host interface and said controllable frequency divider, said USB host interface transmits a response result that said USB host interface configures with USB peripherals for responding to said frequency division controller, according to the response result that is fed back by said USB host interface, said frequency division controller controls and regulates the frequency dividing ratio of said controllable frequency divider in the set scope of the frequency dividing ratio, wherein the frequency dividing ratio is decreased by ⅛ MHz per time until the frequency dividing ratio reaches a minimum value in the set scope;
• wherein said frequency division controller records the response result that is fed back by said USB host interface under every clock, after said USB host interface completes configuring with USB peripherals for responding for one cycle under all clock that is output by said frequency multiplier, according to all the response results in one cycle, said frequency division controller records an effective duration of a clock that said USB host interface configures with USB peripherals for responding, according to the frequency dividing ratio corresponding to a mid point value of the effective duration, said frequency division controller endures a fixed frequency dividing ratio of said controllable frequency divider.