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  1. ec33ddb Mark ab/7061308 as merged in stage. by Xin Li · 3 months ago master
  2. 7f40384 [LSC] Add LOCAL_LICENSE_KINDS to external/walt am: a7906d21cc by Bob Badour · 3 months ago
  3. a7906d2 [LSC] Add LOCAL_LICENSE_KINDS to external/walt by Bob Badour · 3 months ago android-s-preview-1
  4. 26dbaee Mark ab/6881855 as merged am: a7ea31985d by Xin Li · 6 months ago
  5. a7ea319 Mark ab/6881855 as merged by Xin Li · 6 months ago

WALT Latency Timer

DISCLAIMER: This is not an official Google product.

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.
  • Drag latency (scroll).
  • Screen draw latency - using a photodiode that detects whether the screen is black or white.
  • Audio output and microphone latencies.
  • MIDI input and output latencies

The WALT app for Android can be installed from Google Play or downloaded in the releases section; the iOS app must be built from source.

WALT photo


  • Hardware build instructions can be found in this repository under hardware/.
  • Clock synchronization details are described here.
  • The Android/iOS 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.
  • Python code used to communicate with WALT from Linux and ChromeOS can be found here.