AP_HAL: implement DigitalSource abstraction

* GPIO's complement to AnalogSource

libraries/AP_HAL/AP_HAL_Namespace.h

@@ -18,6 +18,7 @@ namespace AP_HAL {
     class Storage;
     class Dataflash;
     class ConsoleDriver;
+    class DigitalSource;
     class GPIO;
     class RCInput;
     class RCOutput;

libraries/AP_HAL/GPIO.h

@@ -9,6 +9,13 @@
 #define GPIO_INPUT  0
 #define GPIO_OUTPUT 1
 
+class AP_HAL::DigitalSource {
+public:
+    virtual void    mode(uint8_t output) = 0;
+    virtual uint8_t read() = 0;
+    virtual void    write(uint8_t value) = 0; 
+};
+
 class AP_HAL::GPIO {
 public:
     GPIO() {}
@@ -16,6 +23,8 @@ public:
     virtual void    pinMode(uint8_t pin, uint8_t output) = 0;
     virtual uint8_t read(uint8_t pin) = 0;
     virtual void    write(uint8_t pin, uint8_t value) = 0;
+    /* Alternative interface: */
+    virtual AP_HAL::DigitalSource* channel(int n) = 0;
 };
 
 #endif // __AP_HAL_GPIO_H__

libraries/AP_HAL_AVR/AP_HAL_AVR_Namespace.h

@@ -18,6 +18,7 @@ namespace AP_HAL_AVR {
     class APM2Dataflash;
     class AVRConsoleDriver;
     class ArduinoGPIO;
+    class ArduinoDigitalSource;
     class APM1RCInput;
     class APM2RCInput;
     class APM1RCOutput;

libraries/AP_HAL_AVR/GPIO.cpp

@@ -6,6 +6,7 @@
 #include "GPIO.h"
 using namespace AP_HAL_AVR;
 
+ArduinoGPIO* ArduinoDigitalSource::parent;
 
 // Get the bit location within the hardware port of the given virtual pin.
 // This comes from the pins_*.c file for the active board configuration.
@@ -81,3 +82,21 @@ void ArduinoGPIO::write(uint8_t pin, uint8_t value) {
     SREG = oldSREG;
 }
 
+AP_HAL::DigitalSource* ArduinoGPIO::channel(int n) {
+  if (ArduinoDigitalSource::parent == NULL) {
+    ArduinoDigitalSource::parent = this;
+  }
+  return new ArduinoDigitalSource(n);
+}
+
+void ArduinoDigitalSource::mode(uint8_t output) {
+  parent->pinMode(_pin, output);
+}
+
+uint8_t ArduinoDigitalSource::read() {
+  return parent->read(_pin);
+}
+
+void ArduinoDigitalSource::write(uint8_t value) {
+  parent->write(_pin, value);
+}

libraries/AP_HAL_AVR/GPIO.h

@@ -5,6 +5,18 @@
 #include <AP_HAL.h>
 #include "AP_HAL_AVR_Namespace.h"
 
+class AP_HAL_AVR::ArduinoDigitalSource : public AP_HAL::DigitalSource {
+public:
+  ArduinoDigitalSource(int pin) : _pin(pin) {}
+  void    mode(uint8_t output);
+  uint8_t read();
+  void    write(uint8_t value);
+
+  static ArduinoGPIO* parent;
+private:
+  int _pin;
+};
+
 class AP_HAL_AVR::ArduinoGPIO : public AP_HAL::GPIO {
 public:
     ArduinoGPIO() {}
@@ -12,6 +24,7 @@ public:
     void    pinMode(uint8_t pin, uint8_t output);
     uint8_t read(uint8_t pin);
     void    write(uint8_t pin, uint8_t value);
+    AP_HAL::DigitalSource* channel(int);
 };
 
 #endif // __AP_HAL_AVR_GPIO_H__