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package raspi
import (
"errors"
"fmt"
"os"
"gobot.io/x/gobot"
"gobot.io/x/gobot/sysfs"
)
// PWMPin is the Raspberry Pi implementation of the PWMPinner interface.
// It uses Pi Blaster.
type PWMPin struct {
pin string
dc uint32
period uint32
}
// NewPwmPin returns a new PWMPin
func NewPWMPin(pin string) *PWMPin {
return &PWMPin{
pin: pin}
}
// Export exports the pin for use by the Raspberry Pi
func (p *PWMPin) Export() error {
return nil
}
// Unexport unexports the pin and releases the pin from the operating system
func (p *PWMPin) Unexport() error {
return p.piBlaster(fmt.Sprintf("release %v\n", p.pin))
}
// Enable enables/disables the PWM pin
func (p *PWMPin) Enable(e bool) (err error) {
return nil
}
// Polarity returns the polarity either normal or inverted
func (p *PWMPin) Polarity() (polarity string, err error) {
return "normal", nil
}
// InvertPolarity does not do anything when using PiBlaster
func (p *PWMPin) InvertPolarity(invert bool) (err error) {
return nil
}
// Period returns the current PWM period for pin
func (p *PWMPin) Period() (period uint32, err error) {
if p.period == 0 {
return p.period, errors.New("Raspi PWM pin period not set")
}
return p.period, nil
}
// SetPeriod uses PiBlaster setting and cannot be changed once set
func (p *PWMPin) SetPeriod(period uint32) (err error) {
if p.period != 0 {
return errors.New("Cannot set the period of individual PWM pins on Raspi")
}
p.period = period
return nil
}
// DutyCycle returns the duty cycle for the pin
func (p *PWMPin) DutyCycle() (duty uint32, err error) {
return p.dc, nil
}
// SetDutyCycle writes the duty cycle to the pin
func (p *PWMPin) SetDutyCycle(duty uint32) (err error) {
if p.period == 0 {
return errors.New("Raspi PWM pin period not set")
}
if duty > p.period {
return errors.New("Duty cycle exceeds period.")
}
p.dc = duty
val := gobot.FromScale(float64(p.dc), 0, float64(p.period))
// never go below minimum allowed duty for pi blaster
if val < 0.05 {
val = 0.05
}
return p.piBlaster(fmt.Sprintf("%v=%v\n", p.pin, val))
}
func (p *PWMPin) piBlaster(data string) (err error) {
fi, err := sysfs.OpenFile("/dev/pi-blaster", os.O_WRONLY|os.O_APPEND, 0644)
defer fi.Close()
if err != nil {
return err
}
_, err = fi.WriteString(data)
return
}
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