Method and apparatus for aligning and synchronizing a remote video signal and a local video signal

Calibration circuitry for calibrating a local raster of a local video subsystem to a remote raster of a remote video subsystem, the remote raster including a plurality of scan lines, each scan line having a scan line period and a visible display line resolution, 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 for generating a remote raster clock signal, the calibration circuitry comprising:

• measurement circuitry for measuring a first duration of a low-level portion of the sync signal and a second duration of a high-level portion of the sync signal, and for adding the first and second durations to provide an estimate of the scan line period,
• mapping circuitry for mapping the visible display line resolution to a total display line resolution that most closely approximates the estimated scan line period, and processing logic for initializing the local raster clock with a initial clock value including logic for initializing the local raster clock to the total display line resolution, the total display line resolution representing the total number of visible and invisible pixels in a scan line, the initialized local raster clock for being 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.

Calibration circuitry for calibrating 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 remote video subsystem including circuitry for generating a graphics object having a predetermined size .sup..DELTA.W graphics, the local video subsystem including a local raster clock and a remote raster clock for generating a remote raster cock signal, the calibration circuitry comprising:

• processing logic for initializing the local raster clock with a initial clock value, the initialized local raster clock for being 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;
• measurement circuitry for calculating a measured size .sup..DELTA.W measured of the graphics object under control to the estimated remote raster clock signal;
• and
• circuitry for scaling the estimated remote raster clock frequency by .sup..DELTA.W graphics.sup./.DELTA.W measured.

In a computer system including a local video subsystem and a remote video subsystem, the remote video subsystem for providing a sync signal to the local 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 for generating a local raster clock signal and the remote raster has a remote raster clock for generating a remote raster clock signal, a method for calibrating the local raster to the remote raster, the method comprising the steps of:

• measuring a first duration of a first phase of the sync signal;
• measuring a second duration of a second phase of the sync signal;
• if the first duration is less than the second duration, determining that the first phase is an active phase;
• and
• if the second duration is less than the first duration, determining that the second phase is the active phase, wherein the active phase corresponds to the polarity of the sync signal, the first phase represents a high-level portion of the sync signal, and the second phase represents a low-level portion of the sync signal.

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 raster including a plurality of scan lines, each scan line having a scan line period, 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:

• measuring a first duration of a low-level portion of the sync signal and a second duration of a high-level portion of the sync signal;
• adding the first and second durations to provide an estimate of the scan line period,
• initializing the local raster clock with an initial clock value the initial clock value being the estimated scan line period;
• 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.

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 remote raster including a plurality of scan lines, each scan line has a scan line period and a visible display line resolution, 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:

• measuring a first duration of a low-level portion of the sync signal and a second duration of a high-level portion of the sync signal;
• adding the first and second durations to provide an estimate of the scan line period,
• initializing the local raster clock with an initial clock value comprising the steps of:
• mapping the visible display line resolution to a total display line resolution that most closely approximates the estimated scan line period;
• and
• setting the initial clock value to the total display line resolution, wherein the total display line resolution represents the total number of visible and invisible pixels in a scan line;
• 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.

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:

• initializing the local raster clock with an initial clock value;
• and
• the remote subsystem generating a graphics object having a predetermined size .DELTA.W.sub.graphics ;
• 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,
• the local subsystem, under control of the estimated remote raster clock signal, calculating a measured size .DELTA.W.sub.measured of the graphics object;
• and
• scaling the estimated remote raster clock frequency by .DELTA.W.sub.graphics /.DELTA.W.sub.measured.