AP_HAL: added device id tuples to Device class

this allows a bus connection and device type tuple to be identifed as
a 24 bit number for use in user visible device IDs. Every bus
connection has a unique device ID.

libraries/AP_HAL/Device.h

@@ -27,8 +27,10 @@
 class AP_HAL::Device {
 public:
     enum BusType {
-        BUS_TYPE_I2C,
-        BUS_TYPE_SPI,
+        BUS_TYPE_UNKNOWN = 0,
+        BUS_TYPE_I2C     = 1,
+        BUS_TYPE_SPI     = 2,
+        BUS_TYPE_UAVCAN  = 3
     };
 
     enum Speed {
@@ -39,11 +41,26 @@ public:
     FUNCTOR_TYPEDEF(PeriodicCb, bool);
     typedef void* PeriodicHandle;
 
-    const enum BusType bus_type;
-
     Device(enum BusType type)
-        : bus_type(type)
-    { }
+    {
+        _bus_id.devid_s.bus_type = type;
+    }
+
+    // return bus type
+    enum BusType bus_type(void) const {
+        return _bus_id.devid_s.bus_type;
+    }
+
+    // return 24 bit bus identifier
+    uint32_t get_bus_id(void) const {
+        return _bus_id.devid;
+    }
+
+    // set device type within a device class (eg. AP_COMPASS_TYPE_LSM303D)
+    void set_device_type(uint8_t devtype) {
+        _bus_id.devid_s.devtype = devtype;
+    }
+    
     
     virtual ~Device() { }
 
@@ -150,6 +167,62 @@ public:
         _read_flag = flag;
     }
 
+
+    /**
+     * make a bus id given bus type, bus number, bus address and
+     * device type This is for use by devices that do not use one of
+     * the standard HAL Device types, such as UAVCAN devices
+     */
+    static uint32_t make_bus_id(enum BusType bus_type, uint8_t bus, uint8_t address, uint8_t devtype) {
+        union DeviceId d;
+        d.devid_s.bus_type = bus_type;
+        d.devid_s.bus = bus;
+        d.devid_s.address = address;
+        d.devid_s.devtype = devtype;
+        return d.devid;
+    }
+
+    /**
+     * return a new bus ID for the same bus connection but a new device type.
+     * This is used for auxillary bus connections
+     */
+    static uint32_t change_bus_id(uint32_t old_id, uint8_t devtype) {
+        union DeviceId d;
+        d.devid = old_id;
+        d.devid_s.devtype = devtype;
+        return d.devid;
+    }
+    
 protected:
     uint8_t _read_flag = 0;
+
+    /*
+      broken out device elements. The bitfields are used to keep
+      the overall value small enough to fit in a float accurately,
+      which makes it possible to transport over the MAVLink
+      parameter protocol without loss of information.
+     */
+    struct DeviceStructure {
+        enum BusType bus_type : 3;
+        uint8_t bus: 5;    // which instance of the bus type
+        uint8_t address;   // address on the bus (eg. I2C address)
+        uint8_t devtype;   // device class specific device type
+    };
+
+    union DeviceId {
+        struct DeviceStructure devid_s;
+        uint32_t devid;
+    };
+    
+    union DeviceId _bus_id;
+
+    // set device address (eg. i2c bus address or spi CS)
+    void set_device_address(uint8_t address) {
+        _bus_id.devid_s.address = address;
+    }
+
+    // set device bus number
+    void set_device_bus(uint8_t bus) {
+        _bus_id.devid_s.bus = bus;
+    }
 };