Method and apparatus for raster calibration
First Claim
1. Calibration circuitry configured to calibrate a local raster of a local video subsystem to a remote raster of a remote video subsystem, the remote video subsystem for providing a sync signal to the local video subsystem, the local video subsystem including a local raster clock and a remote raster clock configured to generate a remote raster clock signal, the calibration circuitry comprising:
- processing logic configured to initialize the local raster clock with an initial clock count corresponding to a frequency of the local raster clock, the initialized local raster clock configured to be phase locked to the sync signal to thereby generate an estimate of the remote raster clock signal, wherein the estimated remote raster clock signal has an estimated remote raster clock frequency.
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Abstract
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.
31 Citations
7 Claims
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1. Calibration circuitry configured to calibrate a local raster of a local video subsystem to a remote raster of a remote video subsystem, the remote video subsystem for providing a sync signal to the local video subsystem, the local video subsystem including a local raster clock and a remote raster clock configured to generate a remote raster clock signal, the calibration circuitry comprising:
processing logic configured to initialize the local raster clock with an initial clock count corresponding to a frequency of the local raster clock, the initialized local raster clock configured to be phase locked to the sync signal to thereby generate an estimate of the remote raster clock signal, wherein the estimated remote raster clock signal has an estimated remote raster clock frequency. - View Dependent Claims (2)
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3. In a computer system including a local video subsystem and a remote video subsystem, wherein the local video subsystem has a local raster and the remote video subsystem has a remote raster, the local raster has a local raster clock and the remote raster has a remote raster clock for generating a remote raster clock signal, the remote video subsystem for providing a sync signal to the local video subsystem, a method for calibrating the local raster to the remote raster, the method comprising the steps of:
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initializing the local raster clock with an initial clock count corresponding to a frequency of the local raster clock; and phase locking the local raster clock to the sync signal, so that the local raster clock generates an estimate of the remote raster clock signal, wherein the estimated remote raster clock signal has an estimated remote raster clock frequency. - View Dependent Claims (4)
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5. A computer system comprising:
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a display device; a bus; a processor coupled to the bus; a remote graphics subsystem coupled to the bus; a local video subsystem coupled to the bus, to the remote graphics subsystem and to the display device, said local video subsystem comprising logic to initialize a local raster clock of the local video subsystem with an initial clock count corresponding to a frequency of the local raster clock, the initialized local raster clock further configured to be phase locked to a sync signal provided by the remote graphics subsystem, said phase locked initialized local raster clock estimating a remote raster clock frequency of the remote graphics subsystem. - View Dependent Claims (6, 7)
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Specification