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38 lines
2.2 KiB
38 lines
2.2 KiB
## WALT Latency Timer ##
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**DISCLAIMER:** This is not an official Google product.
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* [Post about WALT on Android Developers Blog](http://android-developers.blogspot.ca/2016/04/a-new-method-to-measure-touch-and-audio.html)
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* [Instructional videos showing how to use WALT](https://www.youtube.com/playlist?list=PLd6Fi7WgXfcCEJg1FDqNCoQfpWo7W3J5a)
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* [Detailed usage instructions](docs/usage/WALT_usage.md)
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* Mailing list - [walt-discuss](https://groups.google.com/forum/#!forum/walt-discuss)
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* Low-traffic mailing list for major announcements [walt-announce](https://groups.google.com/forum/#!forum/walt-announce)
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WALT is designed to measure the latency of physical sensors and outputs on phones and computers. It can currently perform the following measurements:
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* [Tap latency](docs/TapLatency.md) - time from the moment a finger-like probe touches down (or up) on the screen
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until the kernel timestamps an ACTION_DOWN (or ACTION_UP) event. This physical contact with
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the screen is timed using an accelerometer mounted on the probe.
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* [Drag latency](docs/DragLatency.md) (scroll).
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* [Screen draw latency](docs/ScreenLatency.md) - using a photodiode that detects whether the screen is black or white.
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* [Audio output and microphone latencies](docs/AudioLatency.md).
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* MIDI input and output latencies
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The WALT app for Android can be
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[installed from Google Play](https://play.google.com/store/apps/details?id=org.kamrik.latency.walt)
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or downloaded in the [releases section](https://github.com/google/walt/releases); the iOS app must be built from source.
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## Notes
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* Hardware build instructions can be found in this repository under `hardware/`.
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* Clock synchronization details are described [here](android/WALT/app/src/main/jni/README.md).
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* The Android/iOS device and Teensy clocks have a tendency to diverge due to
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differing clock frequencies. This means they will go out of sync after
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several minutes. The workaround is to use the app to re-sync the
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clocks. Some, but not all tests in the app will sync the clocks when starting a measurement.
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* Python code used to communicate with WALT from Linux and ChromeOS can be found
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[here](https://chromium.googlesource.com/chromiumos/platform/touchbot/+/master/quickstep/).
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