i2c: add interface and implementation to allow i2c devices to be connected to alternate i2c buses than default

Signed-off-by: deadprogram <ron@hybridgroup.com>

drivers/i2c/blinkm_driver.go

@@ -13,6 +13,7 @@ type BlinkMDriver struct {
 	name       string
 	connector  I2cConnector
 	connection I2cConnection
+	I2cBusser
 	gobot.Commander
 }
 
@@ -23,11 +24,16 @@ type BlinkMDriver struct {
 //	Fade - fades the RGB color
 //	FirmwareVersion - returns the version of the current Frimware
 //	Color - returns the color of the LED.
-func NewBlinkMDriver(a I2cConnector) *BlinkMDriver {
+func NewBlinkMDriver(a I2cConnector, options ...func(I2cBusser)) *BlinkMDriver {
 	b := &BlinkMDriver{
 		name:      gobot.DefaultName("BlinkM"),
 		Commander: gobot.NewCommander(),
 		connector: a,
+		I2cBusser: NewI2cBusser(),
+	}
+
+	for _, option := range options {
+		option(b)
 	}
 
 	b.AddCommand("Rgb", func(params map[string]interface{}) interface{} {
@@ -65,8 +71,11 @@ func (b *BlinkMDriver) Connection() gobot.Connection { return b.connection.(gobo
 
 // Start starts the Driver up, and writes start command
 func (b *BlinkMDriver) Start() (err error) {
-	bus := b.connector.I2cGetDefaultBus()
-	b.connection, err = b.connector.I2cGetConnection(blinkmAddress, bus)
+	if b.GetBus() == BusNotInitialized {
+		b.Bus(b.connector.I2cGetDefaultBus())
+	}
+
+	b.connection, err = b.connector.I2cGetConnection(blinkmAddress, b.GetBus())
 	if err != nil {
 		return
 	}

drivers/i2c/i2c.go

@@ -20,6 +20,10 @@ const (
 	Z        = "z"
 )
 
+const (
+	BusNotInitialized = -1
+)
+
 // I2cConnection is a connection to an I2C device with a specified address
 // on a specific bus. Used as an alternative to the I2c interface.
 // Implements sysfs.I2cOperations to talk to the device, wrapping the
@@ -121,3 +125,39 @@ type I2cConnector interface {
 	// I2cGetDefaultBus returns the default I2C bus index
 	I2cGetDefaultBus() int
 }
+
+type i2cBusser struct {
+	bus int
+}
+
+// I2cBusser is the interface which describes how a Driver can specify
+// which I2C bus it wants to use
+type I2cBusser interface {
+	// Bus sets which bus to use
+	Bus(bus int)
+
+	// GetBus gets which bus to use
+	GetBus() int
+}
+
+// NewI2cBusser returns a new I2cBusser.
+func NewI2cBusser() I2cBusser {
+	return &i2cBusser{}
+}
+
+// Bus sets which bus to use
+func (i *i2cBusser) Bus(bus int) {
+	i.bus = bus
+}
+
+// GetBus gets which bus to use
+func (i *i2cBusser) GetBus() int {
+	return i.bus
+}
+
+// Bus sets which bus to use as a optional param
+func Bus(bus int) func(I2cBusser) {
+	return func(i I2cBusser) {
+		i.Bus(bus)
+	}
+}

examples/joule_blinkm.go

@@ -11,10 +11,10 @@ import (
 
 func main() {
 	e := joule.NewAdaptor()
-	blinkm := i2c.NewBlinkMDriver(e)
+	blinkm := i2c.NewBlinkMDriver(e, i2c.Bus(2))
 
 	work := func() {
-		gobot.Every(3*time.Second, func() {
+		gobot.Every(1*time.Second, func() {
 			r := byte(gobot.Rand(255))
 			g := byte(gobot.Rand(255))
 			b := byte(gobot.Rand(255))