bathepawan / walt

A device for measuring latency of physical sensors and outputs on phones and computers

WALT Latency Timer

DISCLAIMER: This is not an official Google product.

Post about WALT on Android Developers Blog

WALT is designed to measure the latency of physical sensors and outputs on phones and computers. It can currently perform the following measurements:

• Tap latency - time from the moment a finger-like probe touches down (or up) on the screen until the kernel timestamps an ACTION_DOWN (or ACTION_UP) event. This physical contact with the screen is timed using an accelerometer mounted on the probe - details
• Drag latency (scroll) - details
• Screen draw latency - using a photodiode that detects whether the screen is black or white.
• Audio output and microphone latencies - details

Notes

• Hardware build instructions can be found in this repository under hardware/
• Clock syncrhonization details are described here
• The Android device and Teensy clocks have a tendency to diverge due to differing clock frequencies. This means they will go out of sync after several minutes. The workaround is to use the app to re-sync the clocks. Some, but not all tests in the app will sync the clocks when starting a measurement.
• The Android app uses some native code. In order to build it run ndk-build in <repo root>/android/WALT/app/src/main before building in Android Studio.
• Python code used to communicate with WALT from Linux and ChromeOS can be found here