hybridgroup.gobot/sysfs/pwm_pin.go

package sysfs

import (
	"os"
	"strconv"
)

// PWMPin is the interface for sysfs PWM interactions
type PWMPinner interface {
	// Export exports the pin for use by the operating system
	Export() error
	// Unexport unexports the pin and releases the pin from the operating system
	Unexport() error
	// Enable enables/disables the PWM pin
	Enable(val string) (err error)
	// Period returns the current PWM period for pin
	Period() (period string, err error)
	// WriteDuty writes the duty cycle to the pin
	WriteDuty(duty string) (err error)
}

type PWMPin struct {
	pin   string
	Chip  string
	write func(path string, data []byte) (i int, err error)
	read  func(path string) ([]byte, error)
}

// NewPwmPin returns a new pwmPin
func NewPWMPin(pin int) *PWMPin {
	return &PWMPin{
		pin:   strconv.Itoa(pin),
		Chip:  "0",
		read:  readPwmFile,
		write: writePwmFile}
}

// Export writes pin to pwm export path
func (p *PWMPin) Export() (err error) {
	_, err = p.write(p.pwmExportPath(), []byte(p.pin))
	return
}

// Unexport writes pin to pwm unexport path
func (p *PWMPin) Unexport() (err error) {
	_, err = p.write(p.pwmUnexportPath(), []byte(p.pin))
	return
}

// Enable writes value to pwm enable path
func (p *PWMPin) Enable(val string) (err error) {
	_, err = p.write(p.pwmEnablePath(), []byte(val))
	return
}

// Period reads from pwm period path and returns value
func (p *PWMPin) Period() (period string, err error) {
	buf, err := p.read(p.pwmPeriodPath())
	if err != nil {
		return
	}
	return string(buf), nil
}

// WriteDuty writes value to pwm duty cycle path
func (p *PWMPin) WriteDuty(duty string) (err error) {
	_, err = p.write(p.pwmDutyCyclePath(), []byte(duty))
	return
}

// pwmPath returns pwm base path
func (p *PWMPin) pwmPath() string {
	return "/sys/class/pwm/pwmchip" + p.Chip
}

// pwmExportPath returns export path
func (p *PWMPin) pwmExportPath() string {
	return p.pwmPath() + "/export"
}

// pwmUnexportPath returns unexport path
func (p *PWMPin) pwmUnexportPath() string {
	return p.pwmPath() + "/unexport"
}

// pwmDutyCyclePath returns duty_cycle path for specified pin
func (p *PWMPin) pwmDutyCyclePath() string {
	return p.pwmPath() + "/pwm" + p.pin + "/duty_cycle"
}

// pwmPeriodPath returns period path for specified pin
func (p *PWMPin) pwmPeriodPath() string {
	return p.pwmPath() + "/pwm" + p.pin + "/period"
}

// pwmEnablePath returns enable path for specified pin
func (p *PWMPin) pwmEnablePath() string {
	return p.pwmPath() + "/pwm" + p.pin + "/enable"
}

func writePwmFile(path string, data []byte) (i int, err error) {
	file, err := OpenFile(path, os.O_WRONLY, 0644)
	defer file.Close()
	if err != nil {
		return
	}

	return file.Write(data)
}

func readPwmFile(path string) ([]byte, error) {
	file, err := OpenFile(path, os.O_RDONLY, 0644)
	defer file.Close()
	if err != nil {
		return make([]byte, 0), err
	}

	buf := make([]byte, 200)
	var i int
	i, err = file.Read(buf)
	if i == 0 {
		return buf, err
	}
	return buf[:i], err
}