walt

WALT Latency Timer

DISCLAIMER: This is not an official Google product.

• Post about WALT on Android Developers Blog
• Instructional videos showing how to use WALT
• Detailed usage instructions
• Mailing list - walt-discuss
• Low-traffic mailing list for major announcements walt-announce

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.

Notes

• 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.