gpio: pwm support for bbb

bbb.go

@@ -1,25 +1,28 @@
 // BeagleBone Black support.
 // The following features are supported on Linux kernel 3.8+
 //
-//	GPIO (both digital (rw) and analog (ro))
+//	GPIO (digital (rw), analog (ro), pwm)
 //	I2C
 //	LED
 
 package embd
 
 import (
+	"errors"
 	"fmt"
 	"io/ioutil"
 	"os"
+	"path"
 	"strconv"
 	"strings"
+	"time"
 )
 
 func init() {
 	Register(HostBBB, func(rev int) *Descriptor {
 		return &Descriptor{
 			GPIODriver: func() GPIODriver {
-				return newGPIODriver(bbbPins, newDigitalPin, newBBBAnalogPin)
+				return newGPIODriver(bbbPins, newDigitalPin, newBBBAnalogPin, newBBBPWMPin)
 			},
 			I2CDriver: newI2CDriver,
 			LEDDriver: func() LEDDriver {
@@ -104,6 +107,53 @@ var bbbLEDMap = LEDMap{
 	"beaglebone:green:usr3": []string{"3", "USR3", "usr3"},
 }
 
+func bbbEnsureFeatureEnabled(id string) error {
+	pattern := "/sys/devices/bone_capemgr.*/slots"
+	file, err := findFirstMatchingFile(pattern)
+	if err != nil {
+		return err
+	}
+	bytes, err := ioutil.ReadFile(file)
+	if err != nil {
+		return err
+	}
+	str := string(bytes)
+	if strings.Contains(str, id) {
+		return nil
+	}
+	slots, err := os.OpenFile(file, os.O_WRONLY, os.ModeExclusive)
+	if err != nil {
+		return err
+	}
+	defer slots.Close()
+	_, err = slots.WriteString(id)
+	return err
+}
+
+// This needs a little more work.
+func bbbEnsureFeatureDisabled(id string) error {
+	pattern := "/sys/devices/bone_capemgr.*/slots"
+	file, err := findFirstMatchingFile(pattern)
+	if err != nil {
+		return err
+	}
+	bytes, err := ioutil.ReadFile(file)
+	if err != nil {
+		return err
+	}
+	str := string(bytes)
+	if !strings.Contains(str, id) {
+		return nil
+	}
+	slots, err := os.OpenFile(file, os.O_WRONLY, os.ModeExclusive)
+	if err != nil {
+		return err
+	}
+	defer slots.Close()
+	_, err = slots.WriteString("-" + id)
+	return err
+}
+
 type bbbAnalogPin struct {
 	n int
 
@@ -139,27 +189,7 @@ func (p *bbbAnalogPin) init() error {
 }
 
 func (p *bbbAnalogPin) ensureEnabled() error {
-	pattern := "/sys/devices/bone_capemgr.*/slots"
-	file, err := findFirstMatchingFile(pattern)
-	if err != nil {
-		return err
-	}
-	bytes, err := ioutil.ReadFile(file)
-	if err != nil {
-		return err
-	}
-	str := string(bytes)
-	if strings.Contains(str, "cape-bone-iio") {
-		return nil
-	}
-	// Not initialized yet
-	slots, err := os.OpenFile(file, os.O_WRONLY, os.ModeExclusive)
-	if err != nil {
-		return err
-	}
-	defer slots.Close()
-	_, err = slots.WriteString("cape-bone-iio")
-	return err
+	return bbbEnsureFeatureEnabled("cape-bone-iio")
 }
 
 func (p *bbbAnalogPin) valueFilePath() (string, error) {
@@ -207,3 +237,187 @@ func (p *bbbAnalogPin) Close() error {
 
 	return nil
 }
+
+const BBBPWMDefaultPolarity = Positive
+const BBBPWMDefaultDuty = 0
+const BBBPWMDefaultPeriod = 500000
+const BBBPWMMaxPulseWidth = 1000000000
+
+type bbbPWMPin struct {
+	n string
+
+	duty     *os.File
+	period   *os.File
+	polarity *os.File
+
+	initialized bool
+}
+
+func newBBBPWMPin(n string) PWMPin {
+	return &bbbPWMPin{n: n}
+}
+
+func (p *bbbPWMPin) N() string {
+	return p.n
+}
+
+func (p *bbbPWMPin) id() string {
+	return "bone_pwm_" + p.n
+}
+
+func (p *bbbPWMPin) init() error {
+	if p.initialized {
+		return nil
+	}
+
+	if err := p.ensurePWMEnabled(); err != nil {
+		return err
+	}
+	if err := p.ensurePinEnabled(); err != nil {
+		return err
+	}
+
+	basePath, err := p.basePath()
+	if err != nil {
+		return err
+	}
+	if err := p.ensurePeriodFileExists(basePath, 500*time.Millisecond); err != nil {
+		return err
+	}
+	if p.period, err = p.periodFile(basePath); err != nil {
+		return err
+	}
+	if p.duty, err = p.dutyFile(basePath); err != nil {
+		return err
+	}
+	if p.polarity, err = p.polarityFile(basePath); err != nil {
+		return err
+	}
+
+	p.initialized = true
+
+	return nil
+}
+
+func (p *bbbPWMPin) ensurePWMEnabled() error {
+	return bbbEnsureFeatureEnabled("am33xx_pwm")
+}
+
+func (p *bbbPWMPin) ensurePinEnabled() error {
+	return bbbEnsureFeatureEnabled(p.id())
+}
+
+func (p *bbbPWMPin) ensurePinDisabled() error {
+	return nil
+	// return bbbEnsureFeatureDisabled(p.id())
+}
+
+func (p *bbbPWMPin) basePath() (string, error) {
+	pattern := "/sys/devices/ocp.*/pwm_test_" + p.n + ".*"
+	return findFirstMatchingFile(pattern)
+}
+
+func (p *bbbPWMPin) openFile(path string) (*os.File, error) {
+	return os.OpenFile(path, os.O_WRONLY, os.ModeExclusive)
+}
+
+func (p *bbbPWMPin) ensurePeriodFileExists(basePath string, d time.Duration) error {
+	path := p.periodFilePath(basePath)
+	timeout := time.After(d)
+
+	for {
+		select {
+		case <-timeout:
+			return errors.New("embd: period file not found before timeout")
+		default:
+			if _, err := os.Stat(path); err == nil {
+				return nil
+			}
+		}
+
+		// We are looping, wait a bit.
+		time.Sleep(10 * time.Millisecond)
+	}
+}
+
+func (p *bbbPWMPin) periodFilePath(basePath string) string {
+	return path.Join(basePath, "period")
+}
+
+func (p *bbbPWMPin) periodFile(basePath string) (*os.File, error) {
+	return p.openFile(p.periodFilePath(basePath))
+}
+
+func (p *bbbPWMPin) dutyFile(basePath string) (*os.File, error) {
+	return p.openFile(path.Join(basePath, "duty"))
+}
+
+func (p *bbbPWMPin) polarityFile(basePath string) (*os.File, error) {
+	return p.openFile(path.Join(basePath, "polarity"))
+}
+
+func (p *bbbPWMPin) SetPeriod(ns int) error {
+	if err := p.init(); err != nil {
+		return err
+	}
+
+	if ns > BBBPWMMaxPulseWidth {
+		return fmt.Errorf("embd: pwm period for %v is out of bounds (must be =< %vns)", p.n, BBBPWMMaxPulseWidth)
+	}
+
+	_, err := p.period.WriteString(strconv.Itoa(ns))
+	return err
+}
+
+func (p *bbbPWMPin) SetDuty(ns int) error {
+	if err := p.init(); err != nil {
+		return err
+	}
+
+	if ns > BBBPWMMaxPulseWidth {
+		return fmt.Errorf("embd: pwm duty for %v is out of bounds (must be =< %vns)", p.n, BBBPWMMaxPulseWidth)
+	}
+
+	_, err := p.duty.WriteString(strconv.Itoa(ns))
+	return err
+}
+
+func (p *bbbPWMPin) SetPolarity(pol Polarity) error {
+	if err := p.init(); err != nil {
+		return err
+	}
+
+	_, err := p.polarity.WriteString(strconv.Itoa(int(pol)))
+	return err
+}
+
+func (p *bbbPWMPin) reset() error {
+	if err := p.SetPolarity(Positive); err != nil {
+		return err
+	}
+	if err := p.SetDuty(BBBPWMDefaultDuty); err != nil {
+		return err
+	}
+	if err := p.SetPeriod(BBBPWMDefaultPeriod); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func (p *bbbPWMPin) Close() error {
+	if !p.initialized {
+		return nil
+	}
+
+	if err := p.reset(); err != nil {
+		return err
+	}
+	if err := p.ensurePinDisabled(); err != nil {
+		return err
+	}
+
+	p.initialized = false
+
+	return nil
+}

gpio.go

@@ -61,6 +61,35 @@ type AnalogPin interface {
 	Close() error
 }
 
+// The Polarity type indicates the polarity of a pwm pin.
+type Polarity int
+
+const (
+	// Positive represents (default) positive polarity.
+	Positive Polarity = iota
+
+	// Negative represents negative polarity.
+	Negative
+)
+
+// PWMPin implements access to a pwm capable GPIO pin.
+type PWMPin interface {
+	// N returns the logical PWM id.
+	N() string
+
+	// SetPeriod sets the period of a pwm pin.
+	SetPeriod(ns int) error
+
+	// SetDuty sets the duty of a pwm pin.
+	SetDuty(ns int) error
+
+	// SetPolarity sets the polarity of a pwm pin.
+	SetPolarity(pol Polarity) error
+
+	// Close releases the resources associated with the pin.
+	Close() error
+}
+
 // GPIODriver implements a generic GPIO driver.
 type GPIODriver interface {
 	// DigitalPin returns a pin capable of doing digital IO.
@@ -69,6 +98,9 @@ type GPIODriver interface {
 	// AnalogPin returns a pin capable of doing analog IO.
 	AnalogPin(key interface{}) (AnalogPin, error)
 
+	// PWMPin returns a pin capable of generating PWM.
+	PWMPin(key interface{}) (PWMPin, error)
+
 	// Close releases the resources associated with the driver.
 	Close() error
 }
@@ -178,3 +210,9 @@ func AnalogRead(key interface{}) (int, error) {
 
 	return pin.Read()
 }
+
+// NewPWMPin returns a PWMPin interface which allows PWM signal
+// generation over a the PWM pin.
+func NewPWMPin(key interface{}) (PWMPin, error) {
+	return gpioDriverInstance.PWMPin(key)
+}

gpiodriver.go

@@ -16,15 +16,17 @@ type gpioDriver struct {
 
 	dpf func(n int) DigitalPin
 	apf func(n int) AnalogPin
+	ppf func(n string) PWMPin
 
 	initializedPins map[string]pin
 }
 
-func newGPIODriver(pinMap PinMap, dpf func(n int) DigitalPin, apf func(n int) AnalogPin) GPIODriver {
+func newGPIODriver(pinMap PinMap, dpf func(n int) DigitalPin, apf func(n int) AnalogPin, ppf func(n string) PWMPin) GPIODriver {
 	return &gpioDriver{
 		pinMap: pinMap,
 		dpf:    dpf,
 		apf:    apf,
+		ppf:    ppf,
 
 		initializedPins: map[string]pin{},
 	}
@@ -62,6 +64,22 @@ func (io *gpioDriver) AnalogPin(key interface{}) (AnalogPin, error) {
 	return p, nil
 }
 
+func (io *gpioDriver) PWMPin(key interface{}) (PWMPin, error) {
+	if io.ppf == nil {
+		return nil, errors.New("gpio: pwm not supported on this host")
+	}
+
+	pd, found := io.pinMap.Lookup(key, CapPWM)
+	if !found {
+		return nil, fmt.Errorf("gpio: could not find pin matching %v", key)
+	}
+
+	p := io.ppf(pd.ID)
+	io.initializedPins[pd.ID] = p
+
+	return p, nil
+}
+
 func (io *gpioDriver) Close() error {
 	for _, p := range io.initializedPins {
 		if err := p.Close(); err != nil {

gpiodriver_test.go

@@ -52,7 +52,7 @@ func TestGpioDriverDigitalPin(t *testing.T) {
 	var pinMap = PinMap{
 		&PinDesc{ID: "P1_1", Aliases: []string{"1"}, Caps: CapDigital, DigitalLogical: 1},
 	}
-	driver := newGPIODriver(pinMap, newFakeDigitalPin, nil)
+	driver := newGPIODriver(pinMap, newFakeDigitalPin, nil, nil)
 	for _, test := range tests {
 		pin, err := driver.DigitalPin(test.key)
 		if err != nil {
@@ -99,7 +99,7 @@ func TestGpioDriverAnalogPin(t *testing.T) {
 	var pinMap = PinMap{
 		&PinDesc{ID: "P1_1", Aliases: []string{"1"}, Caps: CapAnalog, AnalogLogical: 1},
 	}
-	driver := newGPIODriver(pinMap, nil, newFakeAnalogPin)
+	driver := newGPIODriver(pinMap, nil, newFakeAnalogPin, nil)
 	for _, test := range tests {
 		pin, err := driver.AnalogPin(test.key)
 		if err != nil {
@@ -117,7 +117,7 @@ func TestGpioDriverUnavailablePinType(t *testing.T) {
 		&PinDesc{ID: "P1_1", Aliases: []string{"1"}, Caps: CapDigital, DigitalLogical: 1},
 		&PinDesc{ID: "P1_2", Aliases: []string{"1"}, Caps: CapAnalog, AnalogLogical: 1},
 	}
-	driver := newGPIODriver(pinMap, nil, nil)
+	driver := newGPIODriver(pinMap, nil, nil, nil)
 	_, err := driver.DigitalPin(1)
 	if err == nil {
 		t.Fatal("Looking up digital pin 1: did not get error")

rpi.go

@@ -15,7 +15,7 @@ func init() {
 
 		return &Descriptor{
 			GPIODriver: func() GPIODriver {
-				return newGPIODriver(pins, newDigitalPin, nil)
+				return newGPIODriver(pins, newDigitalPin, nil, nil)
 			},
 			I2CDriver: newI2CDriver,
 		}

samples/.gitignore

@@ -13,6 +13,7 @@ ledshort
 lsm303
 mcp4725
 pca9685
+pwm
 servo
 servoblaster
 tmp006

samples/pwm.go

@@ -0,0 +1,30 @@
+// +build ignore
+
+// PWM example, works OOTB on a BBB.
+
+package main
+
+import (
+	"time"
+
+	"github.com/kidoman/embd"
+)
+
+func main() {
+	if err := embd.InitGPIO(); err != nil {
+		panic(err)
+	}
+	defer embd.CloseGPIO()
+
+	pwm, err := embd.NewPWMPin("P9_14")
+	if err != nil {
+		panic(err)
+	}
+	defer pwm.Close()
+
+	if err := pwm.SetDuty(embd.BBBPWMDefaultPeriod / 2); err != nil {
+		panic(err)
+	}
+
+	time.Sleep(1 * time.Second)
+}