Added get_duty_cycle and set_duty_cycle functions

[Andful]

README.md documents functions get_duty_cycle and set_duty_cycle but does not contain its implementations. This pull request should fix that.

[rust-highfive]

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[Andful]

I just saw from commit c3c0d3e020606dea2910d6aa20294d0a6fa09982 that the functions were removed. Either we add the functions back or we should remove the functions from the README.md file.

[posborne]

Hey @Andful, were you able to test this change on hardware to confirm its function. I don't have a setup handy for PWM testing but am find with inclusion if we have confirmed that its working.

[Andful]

@posborne yes. I ran the code in a Onion Omega 2. You can see the program running on this video. I ran the following program.

use sysfs_pwm::Pwm; 
use std::error::Error;

const ONION_OMEGA_MIN_PERIOD : u32 = 25;

const PWM_CHIP: u32 = 0;
const PWM_NUMBER: u32 = 0;

fn main() -> Result<(), Box<dyn Error>> {
    let pwm = Pwm::new(PWM_CHIP, PWM_NUMBER)?;
    let args: Vec<String> = std::env::args().collect();

    let period = ONION_OMEGA_MIN_PERIOD * (args[1].parse::<u32>()?);

    pwm.with_exported(|| {
        pwm.enable(true)?;
        pwm.set_duty_cycle(0.0)?;
        pwm.set_period_ns(period)?;
        let mut values = (0..=period).map(|x| (x as f32)/(period as f32)).collect::<Vec::<f32>>();
        loop{
            for p in values.iter() {
                pwm.set_duty_cycle(*p)?;
                let read_value = pwm.get_duty_cycle()?;
                assert!((read_value*(period as f32) - p*(period as f32)).abs() <= 0.5);
            }
            values.reverse();
        }
    })?;

    Ok(())
}

[bors[bot]]

Build succeeded:

• continuous-integration/travis-ci/push