Psychtoolbox>Datapixx.{mex*} subfunction

isTimeout = Datapixx(‘RegWrRdPixelSync’, pixelSequence [, timeout=255]);

Write local register cache modifications to Datapixx when the specified pixel
sequence appears on the video display, then read back Datapixx register snapshot
to local cache. This is a good way to write Datapixx registers with microsecond
synchronization to a specific location in a video frame, then pause program
execution until after the pixel has passed. All Datapixx Set* functions do fast
writes to a local register cache on the host, and all Datapixx Get* functions do
fast reads from this local register cache. RegWrRdPixelSync writes these cached
register modifications back to the Datapixx over USB, then waits for a fresh
snapshot of the Datapixx registers to be returned over USB. The cache writeback
USB message is sent immediately, but the Datapixx itself waits until the
specified pixel sequence is presented before writing the registers.
-pixelSequence is a two dimensional array of 8-bit pixel values. Each column
contains the RGB values for one pixel in the sequence. The sequence can contain
from 1 to 8 pixels. The array must contain 3 rows; one row for each of the red,
green, and blue pixel components. For example, passing [255 0; 0 255; 0 0] would
wait until a red-green pixel pair is displayed.
Note that a display’s gamma setting can transform pixel values between the frame
buffer and the display. Use the GetVideoLine function to read back which pixel
values are really sent to the display when a pixel sequence is drawn in the
frame buffer. The pixel values returned by GetVideoLine are the values which
should be used in pixelSequence.
-timeout is the maximum number of video frames (0-65535) which the Datapixx
should wait before continuing to process USB traffic. If the timeout is reached
without the specified pixel sequence having been displayed, then the isTimeout
return value will be true, and the pixelSyncTimeout field returned by
GetVideoStatus will be true.
RegWrRdPixelSync returns when registers are read back after the target pixel
sequence has passed, or a timeout occurs.

###See also: RegWrRd, RegWrRdVideoSync, RegWrPixelSync, GetVideoStatus