gpio: digital pin is responsible for exporting/unexporting itself

digitalpin.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"os"
 	"path"
+	"strconv"
 )
 
 type digitalPin struct {
@@ -14,18 +15,23 @@ type digitalPin struct {
 	val       *os.File
 	activeLow *os.File
 	edge      *os.File
+
+	initialized bool
 }
 
-func newDigitalPin(n int) (*digitalPin, error) {
+func newDigitalPin(n int) *digitalPin {
-	p := &digitalPin{n: n}
+	return &digitalPin{n: n}
-	if err := p.init(); err != nil {
-		return nil, err
-	}
-	return p, nil
 }
 
 func (p *digitalPin) init() error {
+	if p.initialized {
+		return nil
+	}
+
 	var err error
+	if err = p.export(); err != nil {
+		return err
+	}
 	if p.dir, err = p.directionFile(); err != nil {
 		return err
 	}
@@ -36,9 +42,31 @@ func (p *digitalPin) init() error {
 		return err
 	}
 
+	p.initialized = true
+
 	return nil
 }
 
+func (p *digitalPin) export() error {
+	exporter, err := os.OpenFile("/sys/class/gpio/export", os.O_WRONLY, os.ModeExclusive)
+	if err != nil {
+		return err
+	}
+	defer exporter.Close()
+	_, err = exporter.WriteString(strconv.Itoa(p.n))
+	return err
+}
+
+func (p *digitalPin) unexport() error {
+	unexporter, err := os.OpenFile("/sys/class/gpio/unexport", os.O_WRONLY, os.ModeExclusive)
+	if err != nil {
+		return err
+	}
+	defer unexporter.Close()
+	_, err = unexporter.WriteString(strconv.Itoa(p.n))
+	return err
+}
+
 func (p *digitalPin) basePath() string {
 	return fmt.Sprintf("/sys/class/gpio/gpio%v", p.n)
 }
@@ -60,6 +88,10 @@ func (p *digitalPin) activeLowFile() (*os.File, error) {
 }
 
 func (p *digitalPin) SetDirection(dir Direction) error {
+	if err := p.init(); err != nil {
+		return err
+	}
+
 	str := "in"
 	if dir == Out {
 		str = "out"
@@ -69,6 +101,10 @@ func (p *digitalPin) SetDirection(dir Direction) error {
 }
 
 func (p *digitalPin) Read() (int, error) {
+	if err := p.init(); err != nil {
+		return 0, err
+	}
+
 	buf := make([]byte, 1)
 	if _, err := p.val.Read(buf); err != nil {
 		return 0, err
@@ -81,6 +117,10 @@ func (p *digitalPin) Read() (int, error) {
 }
 
 func (p *digitalPin) Write(val int) error {
+	if err := p.init(); err != nil {
+		return err
+	}
+
 	str := "0"
 	if val == High {
 		str = "1"
@@ -90,6 +130,10 @@ func (p *digitalPin) Write(val int) error {
 }
 
 func (p *digitalPin) ActiveLow(b bool) error {
+	if err := p.init(); err != nil {
+		return err
+	}
+
 	str := "0"
 	if b {
 		str = "1"
@@ -99,14 +143,18 @@ func (p *digitalPin) ActiveLow(b bool) error {
 }
 
 func (p *digitalPin) PullUp() error {
-	return errors.New("not implemented")
+	return errors.New("gpio: not implemented")
 }
 
 func (p *digitalPin) PullDown() error {
-	return errors.New("not implemented")
+	return errors.New("gpio: not implemented")
 }
 
 func (p *digitalPin) Close() error {
+	if !p.initialized {
+		return nil
+	}
+
 	if err := p.dir.Close(); err != nil {
 		return err
 	}
@@ -119,6 +167,11 @@ func (p *digitalPin) Close() error {
 	if err := p.edge.Close(); err != nil {
 		return err
 	}
+	if err := p.unexport(); err != nil {
+		return err
+	}
+
+	p.initialized = false
 
 	return nil
 }

gpiogeneric.go

@@ -2,8 +2,6 @@ package embd
 
 import (
 	"fmt"
-	"os"
-	"strconv"
 
 	"github.com/golang/glog"
 )
@@ -47,107 +45,67 @@ func (m PinMap) Lookup(k interface{}) (*PinDesc, bool) {
 	return nil, false
 }
 
+type pin interface {
+	Close() error
+}
+
 type gpioDriver struct {
-	exporter, unexporter *os.File
-
-	initialized bool
-
 	pinMap          PinMap
-	initializedPins map[int]*digitalPin
+	initializedPins map[int]pin
 }
 
 func newGPIODriver(pinMap PinMap) *gpioDriver {
 	return &gpioDriver{
 		pinMap:          pinMap,
-		initializedPins: map[int]*digitalPin{},
+		initializedPins: map[int]pin{},
 	}
 }
 
-func (io *gpioDriver) init() error {
-	if io.initialized {
-		return nil
-	}
-
-	var err error
-	if io.exporter, err = os.OpenFile("/sys/class/gpio/export", os.O_WRONLY, os.ModeExclusive); err != nil {
-		return err
-	}
-	if io.unexporter, err = os.OpenFile("/sys/class/gpio/unexport", os.O_WRONLY, os.ModeExclusive); err != nil {
-		return err
-	}
-
-	io.initialized = true
-
-	return nil
-}
-
 func (io *gpioDriver) lookupKey(key interface{}) (*PinDesc, bool) {
 	return io.pinMap.Lookup(key)
 }
 
-func (io *gpioDriver) export(n int) error {
-	_, err := io.exporter.WriteString(strconv.Itoa(n))
-	return err
-}
-
-func (io *gpioDriver) unexport(n int) error {
-	_, err := io.unexporter.WriteString(strconv.Itoa(n))
-	return err
-}
-
 func (io *gpioDriver) digitalPin(key interface{}) (*digitalPin, error) {
 	pd, found := io.lookupKey(key)
 	if !found {
-		err := fmt.Errorf("gpio: could not find pin matching %q", key)
+		return nil, fmt.Errorf("gpio: could not find pin matching %q", key)
-		return nil, err
 	}
 
 	n := pd.N
 
 	p, ok := io.initializedPins[n]
 	if ok {
-		return p, nil
+		dp, ok := p.(*digitalPin)
+		if !ok {
+			return nil, fmt.Errorf("gpio: sorry, pin %q is already initialized for a different mode", key)
+		}
+		return dp, nil
 	}
 
 	if pd.Caps&CapNormal == 0 {
-		err := fmt.Errorf("gpio: sorry, pin %q cannot be used for GPIO", key)
+		return nil, fmt.Errorf("gpio: sorry, pin %q cannot be used for digital io", key)
-		return nil, err
 	}
 
 	if pd.Caps != CapNormal {
-		glog.Infof("gpio: pin %q is not a dedicated GPIO pin. please refer to the system reference manual for more details", key)
+		glog.Infof("gpio: pin %q is not a dedicated digital io pin. please refer to the system reference manual for more details", key)
 	}
 
-	if err := io.export(n); err != nil {
+	dp := newDigitalPin(n)
-		return nil, err
+	io.initializedPins[n] = dp
-	}
 
-	p, err := newDigitalPin(n)
+	return dp, nil
-	if err != nil {
-		io.unexport(n)
-		return nil, err
-	}
-
-	io.initializedPins[n] = p
-
-	return p, nil
 }
 
 func (io *gpioDriver) DigitalPin(key interface{}) (DigitalPin, error) {
-	if err := io.init(); err != nil {
-		return nil, err
-	}
-
 	return io.digitalPin(key)
 }
 
 func (io *gpioDriver) Close() error {
-	for n := range io.initializedPins {
+	for _, p := range io.initializedPins {
-		io.unexport(n)
+		if err := p.Close(); err != nil {
+			return err
+		}
 	}
-
-	io.exporter.Close()
-	io.unexporter.Close()
 
 	return nil
 }