I’ve been seeing inconsistent system deltatime from frame to frame in my own native Android application as well as the nVidia samples that come with the Tegra dev pack. The device I’m running on (1st gen Nexus 7) runs the samples and apps at 60hz without any problems. I’m testing with the simplest examples, like native_subclass, and an app that just clears the screen every frame and nothing else.
Here’s a sampling of what I’m seeing:
dt = deltatime in seconds computed via differences in gettimeofday(),
msdt = deltatime in milliseconds computed via differences in NvEglUtil::getSystemTime()
I/subclasstest( 1887): dt - 0.016605, msdt - 16
I/subclasstest( 1887): dt - 0.017718, msdt - 18
I/subclasstest( 1887): dt - 0.018687, msdt - 19
I/subclasstest( 1887): dt - 0.012853, msdt - 12
I/subclasstest( 1887): dt - 0.016692, msdt - 17
I/subclasstest( 1887): dt - 0.023318, msdt - 23
I/subclasstest( 1887): dt - 0.009956, msdt - 10
I/subclasstest( 1887): dt - 0.016817, msdt - 17
I/subclasstest( 1887): dt - 0.016529, msdt - 17
I/subclasstest( 1887): dt - 0.019066, msdt - 19
I/subclasstest( 1887): dt - 0.015138, msdt - 15
I/subclasstest( 1887): dt - 0.016606, msdt - 17
The deltatimes will average out to ~16.67ms (or 60hz), but from frame to frame the deltas are very inconsistent. This leads me to believe that the Native Activity thread is not tightly bound to vsync. Is this a known issue and is there a way to get the native frame update more in sync with vsync times? I don’t expect 16.67ms every frame, but I would hope to get a variance of less than +/- 1ms.
Larger variances like these are causing hitching since the update delta time isn’t matching the actual frame refresh time. Again, this isn’t a large delta time problem or an issue with ping ponging between 30 and 60 hz. It appears to be an issue with frame updates not starting consistently in lockstep with vsync. Any tips on figuring this out are much appreciated.