PWM With Rust

Using Bash and /sys

P8.13 -> /sys/class/pwm/pwmchip6/pwm1

How is this determined?

# Enable pwm driver
echo am33xx_pwm > /sys/devices/platform/bone_capemgr/slots
echo cape-universal > /sys/devices/platform/bone_capemgr/slots

# Export chip
echo 1 > /sys/class/pwm/pwmchip6/export

# Setup PWM
echo 20000 > /sys/class/pwm/pwmchip6/pwm1/period
echo 10000 > /sys/class/pwm/pwmchip6/pwm1/duty_cycle
echo 1 > /sys/class/pwm/pwmchip6/pwm1/enable

PWM With SysFS Library

Found a pwm library from posborne which works with sysfs: https://github.com/posborne/rust-sysfs-pwm

Add the following to Cargo.toml

[dependencies]
# or latest version
sysfs-pwm = "^0.1.0"

Package does not seem to be found since it is not in carg

[dependencies]
...
sysfs-pwm = {git="https://github.com/posborne/rust-sysfs-pwm.git", branch="master"}

The following script works using sysfs-pwm

extern crate sysfs_pwm;
use sysfs_pwm::{Pwm, Result};

// PIN: EHRPWM2B (P8_13)
const BB_PWM_CHIP: u32 = 6;
const BB_PWM_NUMBER: u32 = 1;

/// Make an LED "breathe" by increasing and
/// decreasing the brightness
fn main() {
    let pwm = Pwm::new(BB_PWM_CHIP, BB_PWM_NUMBER).unwrap(); // number depends on chip, etc.
    pwm.with_exported(|| {
        pwm.enable(true).unwrap();
        pwm.set_period_ns(20_000).unwrap();
        pwm.set_duty_cycle_ns(1000)
    }).unwrap();
}

Note I think using this requires the pwm to be enabled using the capemanager and the pinmux to be set ahead of time.

Resources:

• https://github.com/posborne/rust-sysfs-pwm/blob/master/examples/breathe.rs
• https://groups.google.com/forum/#!category-topic/beagleboard/gpio/1mkf_s_g0vI
• https://github.com/beagleboard/bb.org-overlays/blob/master/examples/BB-BONE-BACONE/example.sh
• https://groups.google.com/forum/#!topic/beagleboard/dkS51WbicTo
• https://briancode.wordpress.com/2015/01/06/working-with-pwm-on-a-beaglebone-black/
• http://stackoverflow.com/questions/29369616/beaglebone-black-pwm-using-c