Updated_PWM

#!/usr/bin/python3

import pathlib
from time import sleep

class PWM:

    def start(duty, freq=2000, polarity=0):
        """ Set up and start the PWM channel. """

        path = pathlib.Path("/dev/bone/pwm/1/b")
        if path == None:
            return None

        period_ns = 1e9 / freq
        duty_ns = (period_ns * (duty / 100.0))

        # export
        try:
            fd = open(path + "/export", 'w')
            fd.write(str(path))
            fd.close()
        except:
            pass
        time.sleep(0.05)    # Give export a chance

        # Duty Cycle - Set to 0 so period can be changed
        try:
            fd = open(pathpwm + "/duty_cycle", 'w')
            fd.write('0')
            fd.close()
        except:
            pass

        # Period
        fd = open(pathpwm + "/period", 'w')
        fd.write(str(int(period_ns)))
        fd.close()

        # Duty Cycle
        fd = open(pathpwm + "/duty_cycle", 'w')
        fd.write(str(int(duty_ns)))
        fd.close()

        # Enable
        fd = open(pathpwm + "/enable", 'w')
        fd.write('1')
        fd.close()

        return 'Started'

    def set_frequency(freq):
        """ Change the frequency

        frequency - frequency in Hz (freq > 0.0) """
        path = Path("/dev/bone/pwm/1")
        pathpwm = path + "/b"

        # compute current duty cycle
        fd = open(pathpwm + "/duty_cycle", 'r')
        duty_cycle_ns = int(fd.read())
        fd.close()

        fd = open(pathpwm + "/period", 'r')
        period_ns = int(fd.read())
        fd.close()

        duty_cycle = duty_cycle_ns/period_ns          # compute current duty cycle as fraction
        period_ns = 1e9 / freq                  # compute new period
        duty_cycle_ns = period_ns*duty_cycle # compute new duty cycle as fraction of period

    # print('duty_cycle: ' + str(duty_cycle))
    # print('period_ns: ' + str(period_ns))
    # print('duty_cycle_ns: ' + str(duty_cycle_ns))

        # Duty Cycle - Set to 0
        fd = open(pathpwm + "/duty_cycle", 'w')
        fd.write('0')
        fd.close()

        # Period
        fd = open(pathpwm + "/period", 'w')
        fd.write(str(int(period_ns)))
        fd.close()

        # Duty Cycle
        fd = open(pathpwm + "/duty_cycle", 'w')
        fd.write(str(int(duty_cycle_ns)))
        fd.close()

    def set_duty_cycle(duty):
        """ Change the duty cycle.

        dutycycle - between 0.0 and 100.0 """
        path = get_pwm_path()
        pathpwm = path + "/b"

        fd = open(pathpwm + "/period", 'r')
        period_ns = int(fd.read())
        fd.close()

        duty_cycle_ns = duty/100 * period_ns
        # Duty Cycle
        fd = open(pathpwm + "/duty_cycle", 'w')
        fd.write(str(int(duty_cycle_ns)))
        fd.close()

    def stop():
        """ Stop the PWM channel. """

        path = pwm_path()
        pathpwm = path + "/b"

        # Disable
        fd = open(pathpwm + "/enable", 'w')
        fd.write('0')
        fd.close()

        # unexport
        fd = open(path + "/unexport", 'w')
        fd.write(str(path[1]))
        fd.close()