Python scripts for WALT Latency Timer on Linux and ChromeOS.
evtest. It will list available input devices and once you enter a device number it will show incoming events when you touch that touchpad / touchscreen.Synopsis:
$ ./walt.py --help
usage: walt.py [-h] [-i INPUT] [-s SERIAL] [-t TYPE] [-l LOGDIR] [-n N]
[-p PORT] [-d]
Run the touchpad drag latency test using WALT Latency Timer
optional arguments:
-h, --help show this help message and exit
-i INPUT, --input INPUT
input device, e.g: 6 or /dev/input/event6 (default: )
-s SERIAL, --serial SERIAL
WALT serial port (default: /dev/ttyACM0)
-t TYPE, --type TYPE Test type: drag|tap|screen|sanity|curve|bridge
(default: drag)
-l LOGDIR, --logdir LOGDIR
where to store logs (default: /tmp)
-n N Number of laser toggles to read (default: 40)
-p PORT, --port PORT Port to listen on for the TCP bridge (default: 50007)
-d, --debug talk more (default: False)
See the tap latency section in Android app usage doc.
Below is output from an example run of a tap latency test that reads touch events from /dev/input/event4 (in this case a touchpad). After 40 events (20 down and 20 up) are detected, the script prints median delays and exits.
The input device option is mandatory since several touch devices might be preset (e.g. touchpad and touch screen). You can use a shorthand notation -i 4 which is expanded to -i /dev/input/event4.
The following must be run as root.
$ ./walt.py -t tap -n 40 -i /dev/input/event4 Starting tap latency test Clock zeroed at 1487105210 (rt 0.250 ms) Event: time 1487105212.048997, type 1 (EV_KEY), code 330 (BTN_TOUCH), value 1 shock t 1990338, tap t 1487105212.048997, tap val 1. dt=63738.9 Event: time 1487105212.262449, type 1 (EV_KEY), code 330 (BTN_TOUCH), value 0 shock t 2219992, tap t 1487105212.262449, tap val 0. dt=47537.0 Event: time 1487105212.702711, type 1 (EV_KEY), code 330 (BTN_TOUCH), value 1 ... Processing data... dt_down = [63.74, 26.96, 27.14 ... dt_up = [47.54, 47.03, 41.52... Median latency, down: 23.9, up: 47.1
See the drag latency section in Android app usage doc.
Below is a drag latency measurement of the trackpad on Asus Flip. The trackpad input device is /dev/input/event4 which was selected using the -i 4 argument.
The -n 20 option tells the script to record 20 laser events. Any change in laser sensor reading counts as one event, therefore one crossing of the beam counts as two events (laser goes off and back on), and a full cycle of the finger going up and down counts as 4 events. This measurement recorded 20/4 = 5 full cycles of the finger moving up and down.
In addition to moving your finger up and down please also move it slowly along the beam. The calculation used by pywalt needs some spread of the x coordinates for better precision.
Drag latency uses evtest and must therefore be run as root.
#./walt.py -t drag -i 4 -n 20 Starting drag latency test Input device : /dev/input/event4 Serial device : /dev/ttyACM1 Laser log file : /tmp/WALT_2017_03_07__1532_12_laser.log evtest log file: /tmp/WALT_2017_03_07__1532_12_evtest.log Clock zeroed at 1488918733 (rt 0.306 ms) .................... Processing data, may take a minute or two... Drag latency (min method) = 21.07 ms