Software PWM Work

examples/software pwm/pwm.go

@@ -0,0 +1,48 @@
+/*
+
+A Software Based PWM example by @Ronin11, using the go-rpio library
+
+Toggles a LED on physical pin 10
+Connect a LED with resistor from pin 10 to ground.
+
+*/
+
+package main
+
+import (
+	"fmt"
+	"os"
+	"time"
+
+	"github.com/Ronin11/go-rpio"
+)
+
+const pin = rpio.Pin(10)
+
+func main() {
+
+	if err := rpio.Open(); err != nil {
+		fmt.Println(err)
+		os.Exit(1)
+	}
+
+	// Unmap gpio memory when done
+	defer rpio.Close()
+
+	//Creates the PWM Signal running on the pin, at 2KHz, with a 0% PWM cycle.
+	pwm := rpio.CreateSofwarePWM(pin, 2000, 0, 32)
+
+	pwm.Start()
+	defer pwm.Stop()
+	// five times smoothly fade in and out
+	for i := 0; i < 5; i++ {
+		for i := uint32(0); i < 32; i++ { // increasing brightness
+				pwm.SetDutyCycle(i, 32)
+				time.Sleep(time.Second/32)
+		}
+		for i := uint32(32); i > 0; i-- { // decreasing brightness
+				pwm.SetDutyCycle(i, 32)
+				time.Sleep(time.Second/32)
+		}
+	}
+}

rpio.go

@@ -79,6 +79,27 @@ type State uint8
 type Pull uint8
 type Edge uint8
 
+type PwmStatus uint8
+const (
+	STOPPED PwmStatus = 0
+	RUNNING PwmStatus = 1
+)
+
+type PwmState uint8
+const (
+	OFF PwmState = 0
+	ON PwmState = 1
+)
+
+type SoftwarePWM struct {
+	pin Pin
+	freq uint32
+	dutyLen uint32
+	cycleLen uint32
+	status PwmStatus
+	state PwmState
+}
+
 // Memory offsets for gpio, see the spec for more details
 const (
 	bcm2835Base = 0x20000000
@@ -547,6 +568,58 @@ func StartPwm() {
 	pwmMem[pwmCtlReg] = pwmMem[pwmCtlReg] | pwen<<8 | pwen
 }
 
+//Create a Software PWM struct
+func CreateSofwarePWM(pin Pin, freq uint32, dutyLen uint32, cycleLen uint32) *SoftwarePWM{
+	//Set pin as Output
+	pin.Output()
+	return &SoftwarePWM{pin: pin, freq: freq, dutyLen: dutyLen, cycleLen: cycleLen}
+}
+
+//Sets the duty cycle for the software PWM
+func (swPwm *SoftwarePWM) SetDutyCycle(dutyLen uint32, cycleLen uint32){
+	swPwm.dutyLen = dutyLen
+	swPwm.cycleLen = cycleLen
+}
+
+//Sets the frequency of the software PWM
+func (swPwm *SoftwarePWM) SetFreq(freq uint32){
+	swPwm.freq = freq
+}
+
+//Starts the software PWM
+func (swPwm *SoftwarePWM) Start(){
+	swPwm.status = RUNNING
+	swPwm.pwmLoop()
+}
+
+//Stops the software PWM
+func (swPwm *SoftwarePWM) Stop(){
+	swPwm.status = STOPPED
+	swPwm.pin.Write(Low)
+}
+
+
+//Internal PWM execution loop
+func (swPwm *SoftwarePWM) pwmLoop(){
+	go func(){
+		var sleepInterval time.Duration
+		for swPwm.status == RUNNING {
+			//sleepInterval is the basic unit of time between pwm 'ticks'
+			sleepInterval = time.Second / time.Duration(swPwm.freq)
+			if swPwm.state == OFF {
+				swPwm.pin.Write(High)
+				swPwm.state = ON
+				sleepInterval = sleepInterval * time.Duration(swPwm.dutyLen)
+			} else {
+				swPwm.pin.Write(Low)
+				swPwm.state = OFF
+				sleepInterval = sleepInterval * time.Duration(swPwm.cycleLen - swPwm.dutyLen)
+			}
+			time.Sleep(sleepInterval)
+		}
+	}()
+}
+
 // Open and memory map GPIO memory range from /dev/mem .
 // Some reflection magic is used to convert it to a unsafe []uint32 pointer
 func Open() (err error) {