Clone this repo:
  1. 84f437d Add default code reviewers into OWNERS by Chih-Hung Hsieh · 3 months ago master oreo-mr1-iot-release simpleperf-release android-o-mr1-iot-release-1.0.10 android-q-preview-1 android-q-preview-2.5
  2. 0894351 DO NOT MERGE by Xin Li · 5 months ago android-o-mr1-iot-release-1.0.7 android-o-mr1-iot-release-1.0.8
  3. d4e5f84 Convert sync_clock_jni to Android.bp by Dan Willemsen · 5 months ago android-wear-8.0.0_r2
  4. 56b988d Merge Android Pie into master am: a096c61e90 am: 9cea0afe51 by Xin Li · 9 months ago android-o-mr1-iot-release-smart-display-r4 android-o-mr1-iot-release-smart-display-r5 android-o-mr1-iot-release-smart-display-r8
  5. 9cea0af Merge Android Pie into master am: a096c61e90 by Xin Li · 9 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.