>Psychtoolbox>PsychTests

VRRFixedRateSwitchingTest([test=’upstep’][, n=2000][, hwmeasurement=0][, testImage][, saveplots=0][, screenNumber=max])

Test accuracy of Fixed refresh rate (FRR) stimulation, while rapid refresh rate
switching is facilitated by use of VRR functionality, aka “FreeSync”, “G-Sync”,
or “DisplayPort Adaptive Sync”.

FRR switching is useful for paradigms where you want to have fine-grained control
over video refresh rate, e.g., to play back movies or show animations at a specific
framerate, and you want very stable timing, but you only occassionally need to
switch framerates. FRR switching is fast, it only takes one or at most two video
refresh cycles. However, during those 1-2 cycles, the display may blank or flicker.
You may want to use FRR switching between consecutive trials to avoid flicker.

Normal VRR modes allow equally fine-grained timing control and perfectly seamless
changes of frame duration on a frame-to-frame basis. However, the current
implementation may be a bit more noisy in terms of timing stability.

The test exercises fast FRR switching on a suitable system. Currently only AMD
graphics cards under Linux X11 with DisplayPort connected VRR display monitors
are supported, no other graphics cards, no HDMI connected displays, no other
displays. You may need to run PsychLinuxConfiguration(), make sure that the
deep color config file gets installed or updated by it, and reboot your machine
once to make this work on many Linux kernels.

It submits OpenGL bufferswaps / flips of varying ‘delay’ between successive
flips and measures and plots how well the hw can follow the requested timing.
When appropriate, the fixed refresh rate of the display is switched via rapid
switching, to achieve a frame interval as close as possible - or identical - to
the requested delay. This works especially well within the VRR range of your
display, typically between 48 Hz and the maximum refresh rate of your display.

Usage:

All parameters are optional.

The ‘test’ parameter selects the test pattern:

‘upstep’ Stepwise increasing duration every 60 flips.

‘downstep’ Stepwise decreasing duration every 60 flips.

‘const’ Run at some constant frame duration.

‘n’ Number of flips / trials to run. 2000 by default.

‘hwmeasurement’ Use external measurement hardware to get timing ground-truth:

0 = Off [Default]. This display a static ‘testImage’ to allow to check how much
the VRR display flickers under different stimulation timing regimes.

1 = VPixx DataPixx or similar VPixx device.

2 = VideoSwitcher + RTBox TTL pulse input port. Works with RTBox, but also with
emulated RTBox of the CRS Bits#. Takes TTL pulse input from the VideoSwitcher.
Selecting this will execute a enable/disable sequence for the VideoSwitcher
at start and end of a measurement session.

3 = CRS Bits# via a loopback cable from trigger out to trigger in BNC port.
Careful: Uses T-Lock for signalling/triggering at stimulus onset and therefore
a rather deficient (mis)design. This works as long as low framerate compensation
does not get triggered, otherwise the reference timestamps from the CRS hardware
will be completely useless and bogus trash!

4 = Like 2 – RtBox pulse input, but for use with a ColorCal2 or photo-diode that
sends a TTL pulse to the RtBox / Bits# BNC trigger input instead of VideoSwitcher.

5 = Measure via a supported photo-diode via PsychPhotodiode().

6 = Produce light-flash pattern to drive external photo-diode. Don’t record yourself.

‘testImage’ Either the name of an image file, or a numeric m x n or m x n x 3
matric with color values. The image read from the image file, or given image
matrix, will be displayed covering the full window in hwmeasurement == 0 mode.
If the parameter is omitted, one of Psychtoolbox default demo images will be
displayed. The purpose of this static image display is to test how much the
display device flickers under different VRR stimulation timings.

‘saveplots’ Should plots with results be saved to filesystem? Defaults to
0 for ‘No’, 1 = ‘Yes’.

‘screenNumber’ Number of screen to test on. Maximum X-Screen by default.

You can abort the test earlier by pressing the ESC key.

The main plot figure will plot actual measured delay between successive flips
(blue) against requested optimal duration (red). It will also show the difference
in green and median error in red at the bottom of the graph. Median/Average error
and standard deviation is printed to the console last. The plot is also saved
to the current working directory as PDF file.