ardupilot/libraries/AP_HAL/Device.h

/*
 * 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"
#include "utility/functor.h"

/*
 * This is an interface abstracting I2C and SPI devices
 */
class AP_HAL::Device {
public:
    enum BusType {
        BUS_TYPE_I2C,
        BUS_TYPE_SPI,
    };

    enum Speed {
        SPEED_HIGH,
        SPEED_LOW,
    };

    FUNCTOR_TYPEDEF(PeriodicCb, bool);
    typedef void* PeriodicHandle;

    const enum BusType bus_type;

    Device(enum BusType type)
        : bus_type(type)
    { }

    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 successfully 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;

    /**
     * Wrapper function over #transfer() to read recv_len registers, starting
     * by first_reg, into the array pointed by recv. The read flag passed to
     * #set_read_flag(uint8_t) is ORed with first_reg before performing the
     * transfer.
     *
     * Return: true on a successful transfer, false on failure.
     */
    bool read_registers(uint8_t first_reg, uint8_t *recv, uint32_t recv_len)
    {
        first_reg |= _read_flag;
        return transfer(&first_reg, 1, recv, recv_len);
    }

    /**
     * Wrapper function over #transfer() to write a byte to the register reg.
     * The transfer is done by sending reg and val in that order.
     *
     * Return: true on a successful transfer, false on failure.
     */
    bool write_register(uint8_t reg, uint8_t val)
    {
        uint8_t buf[2] = { reg, val };
        return transfer(buf, sizeof(buf), nullptr, 0);
    }

    /**
     * Wrapper function over #transfer() to read a sequence of bytes from
     * device. No value is written, differently from the #read_registers()
     * method and hence doesn't include the read flag set by #set_read_flag()
     */
    bool read(uint8_t *recv, uint32_t recv_len)
    {
        return transfer(nullptr, 0, recv, recv_len);
    }

    /*
     * 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
     * call #unregister_callback() or return false on the callback.
     */
    virtual PeriodicHandle register_periodic_callback(uint32_t period_usec, PeriodicCb) = 0;

    /*
     * Adjust the time for the periodic callback registered with
     * #register_periodic_callback. Note that the time will be re-calculated
     * from the moment this call is made and expire after @period_usec.
     *
     * Return: true if periodic callback was sucessfully adjusted, false otherwise.
     */
    virtual bool adjust_periodic_callback(PeriodicHandle h, uint32_t period_usec) = 0;

    /*
     * Cancel a periodic callback on this bus.
     *
     * Return: true if callback was successfully unregistered, false
     * otherwise.
     */
    virtual bool unregister_callback(PeriodicHandle h) { return false; }

    /**
     * Some devices connected on the I2C or SPI bus require a bit to be set on
     * the register address in order to perform a read operation. This sets a
     * flag to be used by #read_registers(). The flag's default value is zero.
     */
    void set_read_flag(uint8_t flag)
    {
        _read_flag = flag;
    }

protected:
    uint8_t _read_flag = 0;
};