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 data rendering device, where the data rendering device comprises:
a processing unit with access to a processing unit clock; and
a data rendering subsystem, that renders data based on a rendering clock crystal that is separate from and independent of the processing unit clock;
wherein the data rendering subsystem is coupled to the processing unit;
wherein the data rendering subsystem receives data blocks from the processing unit at points of time; and
wherein the processing unit computes a virtual clock counter using the sizes of the data blocks, the number of data blocks received over time, and the processing unit clock increment since a last 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 data blocks is not the same.
4. The system of claim 1 , wherein a data packet with a zero-value payload is sent to the data rendering subsystem when no other data is being sent to the rendering subsystem.
5. The system of claim 1 , wherein the data blocks comprise video media data and further comprising a video DAC.
6. The system of claim 1 , wherein the data 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 data when rendering the data.