- support for servo blaster

- servo requires the underlying PWM to support a SetMicroseconds method

controller/pca9685/pca9685.go

@@ -149,6 +149,11 @@ func (d *PCA9685) SetPwm(channel, onTime, offTime int) (err error) {
 	return
 }
 
+func (d *PCA9685) SetMicroseconds(channel, us int) (err error) {
+	offTime := us * d.Freq * pwmControlPoints / 1000000
+	return d.SetPwm(channel, 0, offTime)
+}
+
 // Close stops the controller and resets mode and pwm controller registers.
 func (d *PCA9685) Close() (err error) {
 	if err = d.setup(); err != nil {

controller/servoblaster/servoblaster.go

@@ -0,0 +1,56 @@
+// Package servoblaster allows interfacing with the software servoblaster driver.
+//
+// More details on ServoBlaster at: https://github.com/richardghirst/PiBits/tree/master/ServoBlaster
+package servoblaster
+
+import (
+	"fmt"
+	"log"
+	"os"
+)
+
+// ServoBlaster represents a software RPi PWM/PCM based servo control module.
+type ServoBlaster struct {
+	initialized bool
+	fd          *os.File
+
+	// Debug level.
+	Debug bool
+}
+
+// New creates a new ServoBlaster instance.
+func New() *ServoBlaster {
+	return &ServoBlaster{}
+}
+
+func (d *ServoBlaster) setup() (err error) {
+	if d.initialized {
+		return
+	}
+	if d.fd, err = os.OpenFile("/dev/servoblaster", os.O_WRONLY, os.ModeExclusive); err != nil {
+		return
+	}
+	d.initialized = true
+	return
+}
+
+// SetMicroseconds sends a command to the PWM driver to generate a us wide pulse.
+func (d *ServoBlaster) SetMicroseconds(channel, us int) (err error) {
+	if err = d.setup(); err != nil {
+		return
+	}
+	cmd := fmt.Sprintf("%v=%vus\n", channel, us)
+	if d.Debug {
+		log.Printf("servoblaster: sending command %q", cmd)
+	}
+	_, err = d.fd.WriteString(cmd)
+	return
+}
+
+// Close closes the open driver handle.
+func (d *ServoBlaster) Close() (err error) {
+	if d.fd != nil {
+		err = d.fd.Close()
+	}
+	return
+}