Python script to calibrate a joystick using the evdev interface

evdev-calibrate.py

#!/usr/bin/python

import libevdev
import sys

def adjust_range(axis_min, axis_center, axis_max):
    if ((axis_max - axis_min)//2 + axis_min) > axis_center:
        axis_max = 2*axis_center - axis_min
    else:
        axis_min = 2*axis_center - axis_max
    return (axis_min, axis_center, axis_max)

def value_from_axis(dev, axis, pos):
    print("Move axis {} to its {} and press a button".format(axis.name, pos))
    while True:
        try:
            for e in dev.events():
                if e.matches(axis):
                    print("\x1b[2K", e.value, end="\r")
                elif e.matches(libevdev.EV_KEY, 1):
                    print()
                    return dev.absinfo[axis].value
        except libevdev.EventsDroppedException:
            print('State lost, re-syncing:')
            for e in dev.sync():
                if e.matches(axis):
                    print("\x1b[2K", e.value, end="\r")
                elif e.matches(libevdev.EV_KEY, 1):
                    print()
                    return dev.absinfo[axis].value

with open(sys.argv[1], "rb") as fd:
    dev = libevdev.Device(fd)

    for axis in dev.evbits[libevdev.EV_ABS]:
        axis_min = value_from_axis(dev, axis, "minimum")
        axis_center = value_from_axis(dev, axis, "center")
        axis_max = value_from_axis(dev, axis, "maximum")
        if axis != libevdev.EV_ABS.ABS_THROTTLE:
            axis_min, axis_center, axis_max = adjust_range(axis_min, axis_center, axis_max)
        a = dev.absinfo[axis]
        print("Prev min {}, new {}".format(a.minimum, axis_min))
        print("Prev max {}, new {}".format(a.maximum, axis_max))
        print("Prev flat {}. new 0".format(a.flat))
        a.minimum = axis_min
        a.maximum = axis_max
        a.flat = 0
        dev.absinfo[axis] = a
        dev.sync_absinfo_to_kernel(axis)