| 摘要 |
A method and apparatus for raster calibration is described. Calibration circuitry operates in the context of a local video subsystem which receives at least one sync signal from a remote video (typically graphics) subsystem. The calibration circuitry calibrates a local raster of the local video subsystem to a remote raster of the remote video subsystem. The calibration circuitry includes measurement circuitry for measuring a first duration of a first phase of the sync signal, and for measuring a second duration of a second phase of the sync signal. Processing logic compares the first and second durations and determines that the phase having the shorter duration is an active phase, the active phase corresponding to the polarity of the sync signal. The processing logic also adds the first and second durations to provide an estimate of the scan line period of the remote raster. The calibration circuitry generates an estimate of the remote raster clock frequency by initializing a local raster clock (preferably a PLL) with an initial clock value, and phase locking the local raster dock to the sync signal to thereby generate an estimate of the remote raster clock signal. The initial clock value is set in a variety of ways. The calibration circuitry also confirms the frequency of the estimated remote raster clock signal by comparing a measured size of a graphics object generated by the remote video subsystem with a known size of the object. Further, the calibration circuitry aligns the local and remote rasters.
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