AP_HAL: Add interface for I2C/SPI devices

These interfaces are intended to abstract I2C and SPI devices for
drivers.

libraries/AP_HAL/AP_HAL_Namespace.h

@@ -13,6 +13,7 @@ namespace AP_HAL {
     /* Toplevel class names for drivers: */
     class UARTDriver;
     class I2CDriver;
+    class Device;
 
     class SPIDeviceDriver;
     class SPIDeviceManager;

libraries/AP_HAL/Device.h

@@ -0,0 +1,83 @@
+/// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
+/*
+ * Copyright (C) 2015-2016  Intel Corporation. All rights reserved.
+ *
+ * This file is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This file is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ * See the GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+#pragma once
+
+#include <inttypes.h>
+
+#include "AP_HAL_Namespace.h"
+
+/*
+ * This is an interface abstracting I2C and SPI devices
+ */
+class AP_HAL::Device {
+public:
+    enum Speed {
+        SPEED_HIGH,
+        SPEED_LOW,
+    };
+
+    typedef void PeriodicHandle;
+
+    virtual ~Device() { }
+
+    /*
+     * Set the speed of future transfers. Depending on the bus the speed may
+     * be shared for all devices on the same bus.
+     *
+     * Return: true if speed was succesfully set or platform doesn't implement
+     * it; false otherwise.
+     */
+    virtual bool set_speed(Speed speed)  = 0;
+
+    /*
+     * Core transfer function. This does a single bus transaction which
+     * sends send_len bytes and receives recv_len bytes back from the slave.
+     *
+     * Return: true on a successful transfer, false on failure.
+     */
+    virtual bool transfer(const uint8_t *send, uint32_t send_len,
+                          uint8_t *recv, uint32_t recv_len) = 0;
+
+    /*
+     * Get the semaphore for the bus this device is in.  This is intended for
+     * drivers to use during initialization phase only.
+     */
+    virtual AP_HAL::Semaphore *get_semaphore() = 0;
+
+    /*
+     * Register a periodic callback for this bus. All callbacks on the
+     * same bus are made from the same thread with lock already taken. In
+     * other words, the callback is not executed on the main thread (or the
+     * thread which registered the callback), but in a separate per-bus
+     * thread.
+     *
+     * After registering the periodic callback, the other functions should not
+     * be used anymore from other contexts. If it really needs to be done, the
+     * lock must be taken.
+     *
+     * Return: A handle for this periodic callback. To cancel the callback
+     * delete the handle.
+     */
+    virtual PeriodicHandle *register_periodic_callback(uint32_t period_usec, AP_HAL::MemberProc) = 0;
+
+    /*
+     * Temporary method to get the fd used by this device: it's here only for
+     * allowing to convert old drivers to this new interface
+     */
+    virtual int get_fd() = 0;
+};