Indirect clock measuring and media adjustment
A method for indirectly measuring the clock rate of a media rendering subsystem, in a media rendering device that has a separate hardware clock for rendering the media, by using the rate at which data requests are made of the CPU in the media rendering device and using the CPU clock to provide additional accuracy in measuring the clock rate.
1. A method for indirectly measuring and adjusting the rendering clock of a media rendering device, where the media rendering device comprises:
a processing unit with access to a processing unit clock; and
a media rendering subsystem, that renders media based on a rendering clock crystal that is separate from and independent of the processing unit clock;
a clock synthesizer subsystem;
wherein the rendering clock crystal is used to drive the clock synthesizer subsystem and creates a synthesizer clock from the rendering clock crystal;
wherein the media rendering subsystem is coupled to the processing unit;
wherein the media rendering subsystem receives media data blocks from the processing unit at points of time;
wherein the synthesizer clock controls the rendering clock crystal; and
wherein the processing unit computes a virtual clock counter using the sizes of the media data blocks, the number of media data blocks received over time, and the processing unit clock increment since the last media data request.
2. The system of claim 1 that measures the rate of the rendering clock crystal using an increment of the virtual clock over an interval of time.
3. The system of claim 1 , wherein the size of each media data blocks is not the same.
4. The system of claim 1 , wherein zero value media is sent to the media rendering subsystem when no other media is being sent to the rendering subsystem.
5. The system of claim 1 , wherein the media data blocks comprise video media data and further comprising a video DAC.
6. The system of claim 1 , wherein the media rendering device uses adjustment information derived from a change of the virtual clock over an interval of time to perform a sample rate conversion of the media when rendering the media.