Merge pull request #79 from youngkin/master

Add support for PWM balanced mode

examples/pwmbalanced/pwm.go

@@ -0,0 +1,44 @@
+/*
+
+A PWM example by @youngkin, using the go-rpio library
+
+Fades a PWM hardware pin in and out using PWM mode balanced (vs. markspace)
+*/
+
+package main
+
+import (
+	"os"
+	"time"
+
+	"github.com/stianeikeland/go-rpio/v4"
+)
+
+func main() {
+	err := rpio.Open()
+	if err != nil {
+		os.Exit(1)
+	}
+	defer rpio.Close()
+
+	pin := rpio.Pin(19)
+	pin.Mode(rpio.Pwm)
+	pin.Freq(64000)
+	pin.DutyCycleWithPwmMode(0, 32, rpio.Balanced)
+	// the LED will be blinking at 2000Hz
+	// (source frequency divided by cycle length => 64000/32 = 2000)
+
+	// five times smoothly fade in and out
+	for i := 0; i < 5; i++ {
+		for i := uint32(0); i < 32; i++ { // increasing brightness
+			pin.DutyCycleWithPwmMode(i, 32, rpio.Balanced)
+			time.Sleep(time.Second / 32)
+		}
+		for i := uint32(32); i > 0; i-- { // decreasing brightness
+			pin.DutyCycleWithPwmMode(i, 32, rpio.Balanced)
+			time.Sleep(time.Second / 32)
+		}
+	}
+
+	pin.DutyCycleWithPwmMode(0, 32, rpio.Balanced)
+}

rpio.go

@@ -13,8 +13,8 @@ Also clock/pwm related oparations:
        - Set Duty cycle
 And SPI oparations:
        - SPI transmit/recieve/exchange bytes
-	- Chip select
        - Set speed
+       - Chip select
 
 Example of use:
 
@@ -146,6 +146,12 @@ const (
 	High
 )
 
+// Which PWM algorithm to use, Balanced or Mark/Space
+const (
+	Balanced  = true
+	MarkSpace = false
+)
+
 // Pull Up / Down / Off
 const (
 	PullOff Pull = iota
@@ -222,6 +228,12 @@ func (pin Pin) DutyCycle(dutyLen, cycleLen uint32) {
 	SetDutyCycle(pin, dutyLen, cycleLen)
 }
 
+// DutyCycleWithPwmMode: Set duty cycle for Pwm pin while also specifying which PWM
+// mode to use, Balanced or MarkSpace (see doc of SetDutyCycleWithPwmMode)
+func (pin Pin) DutyCycleWithPwmMode(dutyLen, cycleLen uint32, mode bool) {
+	SetDutyCycleWithPwmMode(pin, dutyLen, cycleLen, mode)
+}
+
 // Mode: Set pin Mode
 func (pin Pin) Mode(mode Mode) {
 	PinMode(pin, mode)
@@ -497,14 +509,14 @@ func PullMode(pin Pin, pull Pull) {
 		case PullUp:
 			p = 1
 		case PullDown:
-			p = 2;
+			p = 2
 		}
 
 		// This is verbatim C code from raspi-gpio.c
 		pullbits := gpioMem[pullreg]
 		pullbits &= ^(3 << pullshift)
 		pullbits |= (p << pullshift)
-		gpioMem[pullreg]= pullbits
+		gpioMem[pullreg] = pullbits
 	} else {
 		// Pull up/down/off register has offset 38 / 39, pull is 37
 		pullClkReg := pin/32 + 38
@@ -627,12 +639,26 @@ func SetFreq(pin Pin, freq int) {
 // The channels are:
 //   channel 1 (pwm0) for pins 12, 18, 40
 //   channel 2 (pwm1) for pins 13, 19, 41, 45.
+//
+// NOTE without root permission this function will simply do nothing successfully
 func SetDutyCycle(pin Pin, dutyLen, cycleLen uint32) {
+	SetDutyCycleWithPwmMode(pin, dutyLen, cycleLen, MarkSpace)
+
+}
+
+// SetDutyCycleWithPwmMode extends SetDutyCycle to allow for the specification of the PWM
+// algorithm to be used, Balanced or Mark/Space. The constants Balanced or MarkSpace
+// as the value. See 'SetDutyCycle(pin, dutyLen, cycleLen)' above for more information
+// regarding how to use 'SetDutyCycleWithPwmMode()'.
+//
+// NOTE without root permission this function will simply do nothing successfully
+func SetDutyCycleWithPwmMode(pin Pin, dutyLen, cycleLen uint32, mode bool) {
 	const pwmCtlReg = 0
 	var (
 		pwmDatReg uint
 		pwmRngReg uint
 		shift     uint // offset inside ctlReg
+
 	)
 
 	switch pin {
@@ -646,20 +672,29 @@ func SetDutyCycle(pin Pin, dutyLen, cycleLen uint32) {
 		shift = 8
 	default:
 		return
+
 	}
 
 	const ctlMask = 255 // ctl setting has 8 bits for each channel
 	const pwen = 1 << 0 // enable pwm
-	const msen = 1 << 7 // use M/S transition instead of pwm algorithm
+	var msen uint32 = 0
+	// The MSEN1 field in the CTL register is at offset 7. This block starts with the assumption
+	// that 'msen' will be associated with channel 'pwm0'. If this is not the case, 'msen' will
+	// be further shifted in the next code block below to the MSEN2 field at offset 15.
+	if mode == MarkSpace {
+		msen = 1 << 7
+	}
 
-	// reset settings
+	// Shifting 'pwen' and 'msen' puts the associated values at the correct offset within the CTL
+	// register ('pwmCtlReg'). In addition, 'msen' is associated with a PWM channel depending on the
+	// value of 'pin' (see above). 'msen' will either stay at offset 7, as set above for channel 'pwm0',
+	// or be shifted 8 bits if the the associated 'pin' is on channel 'pwm1'.
 	pwmMem[pwmCtlReg] = pwmMem[pwmCtlReg]&^(ctlMask<<shift) | msen<<shift | pwen<<shift
+
 	// set duty cycle
 	pwmMem[pwmDatReg] = dutyLen
 	pwmMem[pwmRngReg] = cycleLen
 	time.Sleep(time.Microsecond * 10)
-
-	// NOTE without root permission this changes will simply do nothing successfully
 }
 
 // StopPwm: Stop pwm for both channels