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Blur Buster's G-SYNC 101 Series Discussion

Talk about NVIDIA G-SYNC, a variable refresh rate (VRR) technology. G-SYNC eliminates stutters, tearing, and reduces input lag. List of G-SYNC Monitors.

Re: Blur Buster's G-SYNC 101 Series Discussion

Postby KKNDT » 19 Dec 2018, 00:06

Which scanout diagram is correct while using GSYNC + VSYNC OFF when frame rate is higher than refresh rate?
Refresh cycle : Frame time ~= 3:2

A: similar with pure NO SYNC
B: Part of the current frame (eg. frame 2) will be abandened, the next refresh cycle (cycle 2)starts synchronously with delivery of frame 3 (yellow).

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Re: Blur Buster's G-SYNC 101 Series Discussion

Postby Chief Blur Buster » 19 Dec 2018, 13:46

This thread is not ideally for display engineering style questions. Those should be posted in Area 51, and not in this GSYNC 101 tweaking HOWTO. This discussion may later (in the next few hours) be moved to Area51 once you've read the reply.

Advanced Reading for Advanced Users

Scanout diagram A

However, scanout diagram A needs to contains some thin slices of minimum-possible VBI blanking interval, so corrected diagram A for both VSYNC OFF as well as GSYNC+VSYNC OFF for the situation of continuous "frame-time < refresh-time" (framerate permanently above hz):


The relevant Blur Busters themed scanout diagram is:


The same situation happens with 360fps during 120Hz GSYNC+VSYNC OFF and 120Hz FreeSync+VSYNC OFF. There are implementation differences behind the scenes for GSYNC/FreeSync but the scanout behaviour (because that's where matters from a human vision & latency perspective: displays painting the refresh top-to-bottom, so top edge of a refresh cycles have photons hitting eyes first) is the same; a new refresh cycle cannot be started until right after the minimum-specified VBI size. For FreeSync, the minimum VBI size is dependant on the EDID/DisplayID advertised by the monitor or the custom resolution configured as the current Vertical Total. FreeSync/HDMI VRR/VESA AdaptiveSync -- all interoperably enlarges/reduces the Back Porch (embedded in the Vertical Total number) changing every single refresh cycle to dynamically space the refresh cycles apart, but can be never be below the minimum allowed number.

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