allow lazy initialisation of the drivers

this allows brevity in the sample codes (and should not be misutilized
in real world applications)

gpio.go

@@ -119,10 +119,15 @@ type GPIODriver interface {
 	Close() error
 }
 
+var gpioDriverInitialized bool
 var gpioDriverInstance GPIODriver
 
 // InitGPIO initializes the GPIO driver.
 func InitGPIO() error {
+	if gpioDriverInitialized {
+		return nil
+	}
+
 	desc, err := DescribeHost()
 	if err != nil {
 		return err
@@ -133,6 +138,7 @@ func InitGPIO() error {
 	}
 
 	gpioDriverInstance = desc.GPIODriver()
+	gpioDriverInitialized = true
 
 	return nil
 }
@@ -145,6 +151,10 @@ func CloseGPIO() error {
 // NewDigitalPin returns a DigitalPin interface which allows control over
 // the digital GPIO pin.
 func NewDigitalPin(key interface{}) (DigitalPin, error) {
+	if err := InitGPIO(); err != nil {
+		return nil, err
+	}
+
 	return gpioDriverInstance.DigitalPin(key)
 }
 
@@ -212,6 +222,10 @@ func PullDown(key interface{}) error {
 // NewAnalogPin returns a AnalogPin interface which allows control over
 // the analog GPIO pin.
 func NewAnalogPin(key interface{}) (AnalogPin, error) {
+	if err := InitGPIO(); err != nil {
+		return nil, err
+	}
+
 	return gpioDriverInstance.AnalogPin(key)
 }
 
@@ -228,5 +242,9 @@ func AnalogRead(key interface{}) (int, error) {
 // NewPWMPin returns a PWMPin interface which allows PWM signal
 // generation over a the PWM pin.
 func NewPWMPin(key interface{}) (PWMPin, error) {
+	if err := InitGPIO(); err != nil {
+		return nil, err
+	}
+
 	return gpioDriverInstance.PWMPin(key)
 }

i2c.go

@@ -38,10 +38,15 @@ type I2CDriver interface {
 	Close() error
 }
 
+var i2cDriverInitialized bool
 var i2cDriverInstance I2CDriver
 
 // InitI2C initializes the I2C driver.
 func InitI2C() error {
+	if i2cDriverInitialized {
+		return nil
+	}
+
 	desc, err := DescribeHost()
 	if err != nil {
 		return err
@@ -52,6 +57,7 @@ func InitI2C() error {
 	}
 
 	i2cDriverInstance = desc.I2CDriver()
+	i2cDriverInitialized = true
 
 	return nil
 }
@@ -63,5 +69,9 @@ func CloseI2C() error {
 
 // NewI2CBus returns a I2CBus.
 func NewI2CBus(l byte) I2CBus {
+	if err := InitI2C(); err != nil {
+		panic(err)
+	}
+
 	return i2cDriverInstance.Bus(l)
 }

led.go

@@ -25,10 +25,15 @@ type LEDDriver interface {
 	Close() error
 }
 
+var ledDriverInitialized bool
 var ledDriverInstance LEDDriver
 
 // InitLED initializes the LED driver.
 func InitLED() error {
+	if ledDriverInitialized {
+		return nil
+	}
+
 	desc, err := DescribeHost()
 	if err != nil {
 		return err
@@ -39,6 +44,7 @@ func InitLED() error {
 	}
 
 	ledDriverInstance = desc.LEDDriver()
+	ledDriverInitialized = true
 
 	return nil
 }
@@ -50,6 +56,10 @@ func CloseLED() error {
 
 // NewLED returns a LED interface which allows control over the LED.
 func NewLED(key interface{}) (LED, error) {
+	if err := InitLED(); err != nil {
+		return nil, err
+	}
+
 	return ledDriverInstance.LED(key)
 }