File content as of revision 35:95cb34636703:

#ifndef  _MAVLINK_PROTOCOL_H_
#define  _MAVLINK_PROTOCOL_H_

#include "string.h"
#include "checksum.h"

#include "mavlink_types.h"


/**
 * @brief Initialize the communication stack
 *
 * This function has to be called before using commParseBuffer() to initialize the different status registers.
 *
 * @return Will initialize the different buffers and status registers.
 */
static void mavlink_parse_state_initialize(mavlink_status_t* initStatus)
{
    if ((initStatus->parse_state <= MAVLINK_PARSE_STATE_UNINIT) || (initStatus->parse_state > MAVLINK_PARSE_STATE_GOT_CRC1))
    {
        initStatus->ck_a = 0;
        initStatus->ck_b = 0;
        initStatus->msg_received = 0;
        initStatus->buffer_overrun = 0;
        initStatus->parse_error = 0;
        initStatus->parse_state = MAVLINK_PARSE_STATE_UNINIT;
        initStatus->packet_idx = 0;
        initStatus->packet_rx_drop_count = 0;
        initStatus->packet_rx_success_count = 0;
        initStatus->current_rx_seq = 0;
        initStatus->current_tx_seq = 0;
    }
}

static inline mavlink_status_t* mavlink_get_channel_status(uint8_t chan)
{
    static mavlink_status_t m_mavlink_status[MAVLINK_COMM_NUM_BUFFERS];
    return &m_mavlink_status[chan];
}

/**
 * @brief Finalize a MAVLink message with MAVLINK_COMM_0 as default channel
 *
 * This function calculates the checksum and sets length and aircraft id correctly.
 * It assumes that the message id and the payload are already correctly set. 
 *
 * @warning This function implicitely assumes the message is sent over channel zero.
 *          if the message is sent over a different channel it will reach the receiver
 *          without error, BUT the sequence number might be wrong due to the wrong
 *          channel sequence counter. This will result is wrongly reported excessive
 *          packet loss. Please use @see mavlink_{pack|encode}_headerless and then
 *          @see mavlink_finalize_message_chan before sending for a correct channel
 *          assignment. Please note that the mavlink_msg_xxx_pack and encode functions
 *          assign channel zero as default and thus induce possible loss counter errors.\
 *          They have been left to ensure code compatibility.
 *
 * @see mavlink_finalize_message_chan
 * @param msg Message to finalize
 * @param system_id Id of the sending (this) system, 1-127
 * @param length Message length, usually just the counter incremented while packing the message
 */
 
 
static inline uint16_t mavlink_finalize_message(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id, uint16_t length)
{
    // This code part is the same for all messages;
    uint16_t checksum;
    msg->len = length;
    msg->sysid = system_id;
    msg->compid = component_id;
    // One sequence number per component
    msg->seq = mavlink_get_channel_status(MAVLINK_COMM_0)->current_tx_seq;
    mavlink_get_channel_status(MAVLINK_COMM_0)->current_tx_seq = mavlink_get_channel_status(MAVLINK_COMM_0)->current_tx_seq+1;
    checksum = crc_calculate((uint8_t*)((void*)msg), length + MAVLINK_CORE_HEADER_LEN);
    crc_accumulate(50, &checksum);
    
    msg->ck_a = (uint8_t)(checksum & 0xFF); ///< High byte
    msg->ck_b = (uint8_t)(checksum >> 8); ///< Low byte

    return length + MAVLINK_NUM_NON_STX_PAYLOAD_BYTES;
}

/**
 * @brief Finalize a MAVLink message with channel assignment
 *
 * This function calculates the checksum and sets length and aircraft id correctly.
 * It assumes that the message id and the payload are already correctly set. This function
 * can also be used if the message header has already been written before (as in mavlink_msg_xxx_pack
 * instead of mavlink_msg_xxx_pack_headerless), it just introduces little extra overhead.
 *
 * @param msg Message to finalize
 * @param system_id Id of the sending (this) system, 1-127
 * @param length Message length, usually just the counter incremented while packing the message
 */
static inline uint16_t mavlink_finalize_message_chan(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id, uint8_t chan, uint16_t length)
{
    // This code part is the same for all messages;
    uint16_t checksum;
    msg->len = length;
    msg->sysid = system_id;
    msg->compid = component_id;
    // One sequence number per component
    msg->seq = mavlink_get_channel_status(chan)->current_tx_seq;
    mavlink_get_channel_status(chan)->current_tx_seq = mavlink_get_channel_status(chan)->current_tx_seq+1;
    checksum = crc_calculate((uint8_t*)((void*)msg), length + MAVLINK_CORE_HEADER_LEN);
    msg->ck_a = (uint8_t)(checksum & 0xFF); ///< High byte
    msg->ck_b = (uint8_t)(checksum >> 8); ///< Low byte

    return length + MAVLINK_NUM_NON_STX_PAYLOAD_BYTES;
}

/**
 * @brief Pack a message to send it over a serial byte stream
 */
static inline uint16_t mavlink_msg_to_send_buffer(uint8_t* buffer, const mavlink_message_t* msg)
{
    *(buffer+0) = MAVLINK_STX; ///< Start transmit
    memcpy((buffer+1), msg, msg->len + MAVLINK_CORE_HEADER_LEN); ///< Core header plus payload
    *(buffer + msg->len + MAVLINK_CORE_HEADER_LEN + 1) = msg->ck_a;
    *(buffer + msg->len + MAVLINK_CORE_HEADER_LEN + 2) = msg->ck_b;
    return msg->len + MAVLINK_NUM_NON_PAYLOAD_BYTES;
    //return 0;
}

/**
 * @brief Get the required buffer size for this message
 */
static inline uint16_t mavlink_msg_get_send_buffer_length(const mavlink_message_t* msg)
{
    return msg->len + MAVLINK_NUM_NON_PAYLOAD_BYTES;
}

union checksum_ {
    uint16_t s;
    uint8_t c[2];
};

union __mavlink_bitfield {
    uint8_t uint8;
    int8_t int8;
    uint16_t uint16;
    int16_t int16;
    uint32_t uint32;
    int32_t int32;
};


static inline void mavlink_start_checksum(mavlink_message_t* msg)
{
    union checksum_ ck;
    crc_init(&(ck.s));
    msg->ck_a = ck.c[0];
    msg->ck_b = ck.c[1];
}

static inline void mavlink_update_checksum(mavlink_message_t* msg, uint8_t c)
{
    union checksum_ ck;
    ck.c[0] = msg->ck_a;
    ck.c[1] = msg->ck_b;
    crc_accumulate(c, &(ck.s));
    msg->ck_a = ck.c[0];
    msg->ck_b = ck.c[1];
}

/**
 * This is a convenience function which handles the complete MAVLink parsing.
 * the function will parse one byte at a time and return the complete packet once
 * it could be successfully decoded. Checksum and other failures will be silently
 * ignored.
 *
 * @param chan     ID of the current channel. This allows to parse different channels with this function.
 *                 a channel is not a physical message channel like a serial port, but a logic partition of
 *                 the communication streams in this case. COMM_NB is the limit for the number of channels
 *                 on MCU (e.g. ARM7), while COMM_NB_HIGH is the limit for the number of channels in Linux/Windows
 * @param c        The char to barse
 *
 * @param returnMsg NULL if no message could be decoded, the message data else
 * @return 0 if no message could be decoded, 1 else
 *
 * A typical use scenario of this function call is:
 *
 * @code
 * #include <inttypes.h> // For fixed-width uint8_t type
 *
 * mavlink_message_t msg;
 * int chan = 0;
 *
 *
 * while(serial.bytesAvailable > 0)
 * {
 *   uint8_t byte = serial.getNextByte();
 *   if (mavlink_parse_char(chan, byte, &msg))
 *     {
 *     printf("Received message with ID %d, sequence: %d from component %d of system %d", msg.msgid, msg.seq, msg.compid, msg.sysid);
 *     }
 * }
 *
 *
 * @endcode
 */
static inline uint8_t mavlink_parse_char(uint8_t chan, uint8_t c, mavlink_message_t* r_message, mavlink_status_t* r_mavlink_status)
{
    static mavlink_message_t m_mavlink_message[MAVLINK_COMM_NUM_BUFFERS];

    // Initializes only once, values keep unchanged after first initialization
    mavlink_parse_state_initialize(mavlink_get_channel_status(chan));

    mavlink_message_t* rxmsg = &m_mavlink_message[chan]; ///< The currently decoded message
    mavlink_status_t* status = mavlink_get_channel_status(chan); ///< The current decode status
    int bufferIndex = 0;

    status->msg_received = 0;

    switch (status->parse_state)
    {
    case MAVLINK_PARSE_STATE_UNINIT:
    case MAVLINK_PARSE_STATE_IDLE:
        if (c == MAVLINK_STX)
        {
            status->parse_state = MAVLINK_PARSE_STATE_GOT_STX;
            mavlink_start_checksum(rxmsg);
        }
        break;

    case MAVLINK_PARSE_STATE_GOT_STX:
        if (status->msg_received)
        {
            status->buffer_overrun++;
            status->parse_error++;
            status->msg_received = 0;
            status->parse_state = MAVLINK_PARSE_STATE_IDLE;
        }
        else
        {
            // NOT counting STX, LENGTH, SEQ, SYSID, COMPID, MSGID, CRC1 and CRC2
            rxmsg->len = c;
            status->packet_idx = 0;
            mavlink_update_checksum(rxmsg, c);
            status->parse_state = MAVLINK_PARSE_STATE_GOT_LENGTH;
        }
        break;

    case MAVLINK_PARSE_STATE_GOT_LENGTH:
        rxmsg->seq = c;
        mavlink_update_checksum(rxmsg, c);
        status->parse_state = MAVLINK_PARSE_STATE_GOT_SEQ;
        break;

    case MAVLINK_PARSE_STATE_GOT_SEQ:
        rxmsg->sysid = c;
        mavlink_update_checksum(rxmsg, c);
        status->parse_state = MAVLINK_PARSE_STATE_GOT_SYSID;
        break;

    case MAVLINK_PARSE_STATE_GOT_SYSID:
        rxmsg->compid = c;
        mavlink_update_checksum(rxmsg, c);
        status->parse_state = MAVLINK_PARSE_STATE_GOT_COMPID;
        break;

    case MAVLINK_PARSE_STATE_GOT_COMPID:
        rxmsg->msgid = c;
        mavlink_update_checksum(rxmsg, c);
        if (rxmsg->len == 0)
        {
            status->parse_state = MAVLINK_PARSE_STATE_GOT_PAYLOAD;
        }
        else
        {
            status->parse_state = MAVLINK_PARSE_STATE_GOT_MSGID;
        }
        break;

    case MAVLINK_PARSE_STATE_GOT_MSGID:
        rxmsg->payload[status->packet_idx++] = c;
        mavlink_update_checksum(rxmsg, c);
        if (status->packet_idx == rxmsg->len)
        {
            status->parse_state = MAVLINK_PARSE_STATE_GOT_PAYLOAD;
        }
        break;

    case MAVLINK_PARSE_STATE_GOT_PAYLOAD:
        /*if (c != rxmsg->ck_a)
        {
            // Check first checksum byte
            status->parse_error++;
            status->msg_received = 0;
            status->parse_state = MAVLINK_PARSE_STATE_IDLE;
            if (c == MAVLINK_STX)
            {
                status->parse_state = MAVLINK_PARSE_STATE_GOT_STX;
                mavlink_start_checksum(rxmsg);
            }
        }
        else
        {
            status->parse_state = MAVLINK_PARSE_STATE_GOT_CRC1;
        }*/
        status->parse_state = MAVLINK_PARSE_STATE_GOT_CRC1;
        break;

    case MAVLINK_PARSE_STATE_GOT_CRC1:
        /*if (c != rxmsg->ck_b)
        {// Check second checksum byte
            status->parse_error++;
            status->msg_received = 0;
            status->parse_state = MAVLINK_PARSE_STATE_IDLE;
            if (c == MAVLINK_STX)
            {
                status->parse_state = MAVLINK_PARSE_STATE_GOT_STX;
                mavlink_start_checksum(rxmsg);
            }
        }
        else
        {
            // Successfully got message
            status->msg_received = 1;
            status->parse_state = MAVLINK_PARSE_STATE_IDLE;
            memcpy(r_message, rxmsg, sizeof(mavlink_message_t));
        }*/
        status->msg_received = 1;
        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
        memcpy(r_message, rxmsg, sizeof(mavlink_message_t));
        break;
    }

    bufferIndex++;
    // If a message has been sucessfully decoded, check index
    if (status->msg_received == 1)
    {
        //while(status->current_seq != rxmsg->seq)
        //{
        //    status->packet_rx_drop_count++;
        //               status->current_seq++;
        //}
        status->current_rx_seq = rxmsg->seq;
        // Initial condition: If no packet has been received so far, drop count is undefined
        if (status->packet_rx_success_count == 0) status->packet_rx_drop_count = 0;
        // Count this packet as received
        status->packet_rx_success_count++;
    }

    r_mavlink_status->current_rx_seq = status->current_rx_seq+1;
    r_mavlink_status->packet_rx_success_count = status->packet_rx_success_count;
    r_mavlink_status->packet_rx_drop_count = status->parse_error;
    status->parse_error = 0;
    return status->msg_received;
}


/**
 * This is a convenience function which handles the complete MAVLink parsing.
 * the function will parse one byte at a time and return the complete packet once
 * it could be successfully decoded. Checksum and other failures will be silently
 * ignored.
 *
 * @param chan     ID of the current channel. This allows to parse different channels with this function.
 *                 a channel is not a physical message channel like a serial port, but a logic partition of
 *                 the communication streams in this case. COMM_NB is the limit for the number of channels
 *                 on MCU (e.g. ARM7), while COMM_NB_HIGH is the limit for the number of channels in Linux/Windows
 * @param c        The char to barse
 *
 * @param returnMsg NULL if no message could be decoded, the message data else
 * @return 0 if no message could be decoded, 1 else
 *
 * A typical use scenario of this function call is:
 *
 * @code
 * #include <inttypes.h> // For fixed-width uint8_t type
 *
 * mavlink_message_t msg;
 * int chan = 0;
 *
 *
 * while(serial.bytesAvailable > 0)
 * {
 *   uint8_t byte = serial.getNextByte();
 *   if (mavlink_parse_char(chan, byte, &msg))
 *     {
 *     printf("Received message with ID %d, sequence: %d from component %d of system %d", msg.msgid, msg.seq, msg.compid, msg.sysid);
 *     }
 * }
 *
 *
 * @endcode
 */

#define MAVLINK_PACKET_START_CANDIDATES 50
/*
static inline uint8_t mavlink_parse_char_new(uint8_t chan, uint8_t c, mavlink_message_t* r_message, mavlink_status_t* r_mavlink_status)
{
        static mavlink_status_t m_mavlink_status[MAVLINK_COMM_NUM_BUFFERS];
        static uint8_t m_msgbuf[MAVLINK_COMM_NUM_BUFFERS][MAVLINK_MAX_PACKET_LEN * 2];
        static uint8_t m_msgbuf_index[MAVLINK_COMM_NUM_BUFFERS];
        static mavlink_message_t m_mavlink_message[MAVLINK_COMM_NUM_BUFFERS];
        static uint8_t m_packet_start[MAVLINK_COMM_NUM_BUFFERS][MAVLINK_PACKET_START_CANDIDATES];
        static uint8_t m_packet_start_index_read[MAVLINK_COMM_NUM_BUFFERS];
        static uint8_t m_packet_start_index_write[MAVLINK_COMM_NUM_BUFFERS];

        // Set a packet start candidate index if sign is start sign
        if (c == MAVLINK_STX)
        {
            m_packet_start[chan][++(m_packet_start_index_write[chan]) % MAVLINK_PACKET_START_CANDIDATES] = m_msgbuf_index[chan];
        }

        // Parse normally, if a CRC mismatch occurs retry with the next packet index
}
//    static mavlink_status_t m_mavlink_status[MAVLINK_COMM_NUM_BUFFERS];
//    static mavlink_message_t m_mavlink_message[MAVLINK_COMM_NUM_BUFFERS];
//// Initializes only once, values keep unchanged after first initialization
//    mavlink_parse_state_initialize(&m_mavlink_status[chan]);
//
//mavlink_message_t* rxmsg = &m_mavlink_message[chan]; ///< The currently decoded message
//mavlink_status_t* status = &m_mavlink_status[chan]; ///< The current decode status
//int bufferIndex = 0;
//
//status->msg_received = 0;
//
//switch (status->parse_state)
//{
//case MAVLINK_PARSE_STATE_UNINIT:
//case MAVLINK_PARSE_STATE_IDLE:
//            if (c == MAVLINK_STX)
//    {
//        status->parse_state = MAVLINK_PARSE_STATE_GOT_STX;
//        mavlink_start_checksum(rxmsg);
//    }
//    break;
//
//case MAVLINK_PARSE_STATE_GOT_STX:
//    if (status->msg_received)
//    {
//        status->buffer_overrun++;
//        status->parse_error++;
//        status->msg_received = 0;
//        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
//    }
//    else
//    {
//        // NOT counting STX, LENGTH, SEQ, SYSID, COMPID, MSGID, CRC1 and CRC2
//        rxmsg->len = c;
//        status->packet_idx = 0;
//        mavlink_update_checksum(rxmsg, c);
//        status->parse_state = MAVLINK_PARSE_STATE_GOT_LENGTH;
//    }
//    break;
//
//case MAVLINK_PARSE_STATE_GOT_LENGTH:
//    rxmsg->seq = c;
//    mavlink_update_checksum(rxmsg, c);
//    status->parse_state = MAVLINK_PARSE_STATE_GOT_SEQ;
//    break;
//
//case MAVLINK_PARSE_STATE_GOT_SEQ:
//    rxmsg->sysid = c;
//    mavlink_update_checksum(rxmsg, c);
//    status->parse_state = MAVLINK_PARSE_STATE_GOT_SYSID;
//    break;
//
//case MAVLINK_PARSE_STATE_GOT_SYSID:
//    rxmsg->compid = c;
//    mavlink_update_checksum(rxmsg, c);
//    status->parse_state = MAVLINK_PARSE_STATE_GOT_COMPID;
//    break;
//
//case MAVLINK_PARSE_STATE_GOT_COMPID:
//    rxmsg->msgid = c;
//    mavlink_update_checksum(rxmsg, c);
//    if (rxmsg->len == 0)
//    {
//        status->parse_state = MAVLINK_PARSE_STATE_GOT_PAYLOAD;
//    }
//    else
//    {
//        status->parse_state = MAVLINK_PARSE_STATE_GOT_MSGID;
//    }
//    break;
//
//case MAVLINK_PARSE_STATE_GOT_MSGID:
//    rxmsg->payload[status->packet_idx++] = c;
//    mavlink_update_checksum(rxmsg, c);
//    if (status->packet_idx == rxmsg->len)
//    {
//        status->parse_state = MAVLINK_PARSE_STATE_GOT_PAYLOAD;
//    }
//    break;
//
//case MAVLINK_PARSE_STATE_GOT_PAYLOAD:
//    if (c != rxmsg->ck_a)
//    {
//        // Check first checksum byte
//        status->parse_error++;
//        status->msg_received = 0;
//        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
//    }
//    else
//    {
//        status->parse_state = MAVLINK_PARSE_STATE_GOT_CRC1;
//    }
//    break;
//
//case MAVLINK_PARSE_STATE_GOT_CRC1:
//    if (c != rxmsg->ck_b)
//    {// Check second checksum byte
//        status->parse_error++;
//        status->msg_received = 0;
//        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
//    }
//    else
//    {
//        // Successfully got message
//        status->msg_received = 1;
//        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
//        memcpy(r_message, rxmsg, sizeof(mavlink_message_t));
//    }
//    break;
//}

bufferIndex++;
// If a message has been sucessfully decoded, check index
if (status->msg_received == 1)
{
    //while(status->current_seq != rxmsg->seq)
    //{
    //    status->packet_rx_drop_count++;
    //               status->current_seq++;
    //}
    status->current_seq = rxmsg->seq;
    // Initial condition: If no packet has been received so far, drop count is undefined
    if (status->packet_rx_success_count == 0) status->packet_rx_drop_count = 0;
    // Count this packet as received
    status->packet_rx_success_count++;
}

r_mavlink_status->current_seq = status->current_seq+1;
r_mavlink_status->packet_rx_success_count = status->packet_rx_success_count;
r_mavlink_status->packet_rx_drop_count = status->parse_error;
return status->msg_received;
}
 */


typedef union __generic_16bit
{
    uint8_t b[2];
    int16_t s;
} generic_16bit;

typedef union __generic_32bit
{
    uint8_t b[4];
    float f;
    int32_t i;
    int16_t s;
} generic_32bit;

typedef union __generic_64bit
{
    uint8_t b[8];
    int64_t ll; ///< Long long (64 bit)
    double  d;  ///< IEEE-754 double precision floating point
} generic_64bit;

/**
 * @brief Place an unsigned byte into the buffer
 *
 * @param b the byte to add
 * @param bindex the position in the packet
 * @param buffer the packet buffer
 * @return the new position of the last used byte in the buffer
 */
static inline uint8_t put_uint8_t_by_index(uint8_t b, uint8_t bindex, uint8_t* buffer)
{
    *(buffer + bindex) = b;
    return sizeof(b);
}

/**
 * @brief Place a signed byte into the buffer
 *
 * @param b the byte to add
 * @param bindex the position in the packet
 * @param buffer the packet buffer
 * @return the new position of the last used byte in the buffer
 */
static inline uint8_t put_int8_t_by_index(int8_t b, int8_t bindex, uint8_t* buffer)
{
    *(buffer + bindex) = (uint8_t)b;
    return sizeof(b);
}

/**
 * @brief Place two unsigned bytes into the buffer
 *
 * @param b the bytes to add
 * @param bindex the position in the packet
 * @param buffer the packet buffer
 * @return the new position of the last used byte in the buffer
 */
static inline uint8_t put_uint16_t_by_index(uint16_t b, const uint8_t bindex, uint8_t* buffer)
{
    buffer[bindex]   = (b>>8)&0xff;
    buffer[bindex+1] = (b & 0xff);
    return sizeof(b);
}

/**
 * @brief Place two signed bytes into the buffer
 *
 * @param b the bytes to add
 * @param bindex the position in the packet
 * @param buffer the packet buffer
 * @return the new position of the last used byte in the buffer
 */
static inline uint8_t put_int16_t_by_index(int16_t b, uint8_t bindex, uint8_t* buffer)
{
    return put_uint16_t_by_index(b, bindex, buffer);
}

/**
 * @brief Place four unsigned bytes into the buffer
 *
 * @param b the bytes to add
 * @param bindex the position in the packet
 * @param buffer the packet buffer
 * @return the new position of the last used byte in the buffer
 */
static inline uint8_t put_uint32_t_by_index(uint32_t b, const uint8_t bindex, uint8_t* buffer)
{
    buffer[bindex]   = (b>>24)&0xff;
    buffer[bindex+1] = (b>>16)&0xff;
    buffer[bindex+2] = (b>>8)&0xff;
    buffer[bindex+3] = (b & 0xff);
    return sizeof(b);
}

/**
 * @brief Place four signed bytes into the buffer
 *
 * @param b the bytes to add
 * @param bindex the position in the packet
 * @param buffer the packet buffer
 * @return the new position of the last used byte in the buffer
 */
static inline uint8_t put_int32_t_by_index(int32_t b, uint8_t bindex, uint8_t* buffer)
{
    buffer[bindex]   = (b>>24)&0xff;
    buffer[bindex+1] = (b>>16)&0xff;
    buffer[bindex+2] = (b>>8)&0xff;
    buffer[bindex+3] = (b & 0xff);
    return sizeof(b);
}

/**
 * @brief Place four unsigned bytes into the buffer
 *
 * @param b the bytes to add
 * @param bindex the position in the packet
 * @param buffer the packet buffer
 * @return the new position of the last used byte in the buffer
 */
static inline uint8_t put_uint64_t_by_index(uint64_t b, const uint8_t bindex, uint8_t* buffer)
{
    buffer[bindex]   = (b>>56)&0xff;
    buffer[bindex+1] = (b>>48)&0xff;
    buffer[bindex+2] = (b>>40)&0xff;
    buffer[bindex+3] = (b>>32)&0xff;
    buffer[bindex+4] = (b>>24)&0xff;
    buffer[bindex+5] = (b>>16)&0xff;
    buffer[bindex+6] = (b>>8)&0xff;
    buffer[bindex+7] = (b & 0xff);
    return sizeof(b);
}

/**
 * @brief Place four signed bytes into the buffer
 *
 * @param b the bytes to add
 * @param bindex the position in the packet
 * @param buffer the packet buffer
 * @return the new position of the last used byte in the buffer
 */
static inline uint8_t put_int64_t_by_index(int64_t b, uint8_t bindex, uint8_t* buffer)
{
    return put_uint64_t_by_index(b, bindex, buffer);
}

/**
 * @brief Place a float into the buffer
 *
 * @param b the float to add
 * @param bindex the position in the packet
 * @param buffer the packet buffer
 * @return the new position of the last used byte in the buffer
 */
static inline uint8_t put_float_by_index(float b, uint8_t bindex, uint8_t* buffer)
{
    generic_32bit g;
    g.f = b;
    return put_int32_t_by_index(g.i, bindex, buffer);
}

/**
 * @brief Place a double into the buffer
 *
 * @param b the double to add
 * @param bindex the position in the packet
 * @param buffer the packet buffer
 * @return the new position of the last used byte in the buffer
 */
static inline uint8_t put_double_by_index(double b, uint8_t bindex, uint8_t* buffer)
{
    generic_64bit g;
    g.d = b;
    return put_int64_t_by_index(g.ll, bindex, buffer);
}

/**
 * @brief Place an array into the buffer
 *
 * @param b the array to add
 * @param length size of the array (for strings: length WITH '\0' char)
 * @param bindex the position in the packet
 * @param buffer packet buffer
 * @return new position of the last used byte in the buffer
 */
static inline uint8_t put_array_by_index(const int8_t* b, uint8_t length, uint8_t bindex, uint8_t* buffer)
{
    memcpy(buffer+bindex, b, length);
    return length;
}

/**
 * @brief Place a string into the buffer
 *
 * @param b the string to add
 * @param maxlength size of the array (for strings: length WITHOUT '\0' char)
 * @param bindex the position in the packet
 * @param buffer packet buffer
 * @return new position of the last used byte in the buffer
 */
static inline uint8_t put_string_by_index(const char* b, uint8_t maxlength, uint8_t bindex, uint8_t* buffer)
{
    uint16_t length = 0;
    // Copy string into buffer, ensuring not to exceed the buffer size
    int i;
    for (i = 1; i < maxlength; i++)
    {
        length++;
        // String characters
        if (i < (maxlength - 1))
        {
            buffer[bindex+i] = b[i];
            // Stop at null character
            if (b[i] == '\0')
            {
                break;
            }
        }
        // Enforce null termination at end of buffer
        else if (i == (maxlength - 1))
        {
            buffer[i] = '\0';
        }
    }
    // Write length into first field
    put_uint8_t_by_index(length, bindex, buffer);
    return length;
}

/**
 * @brief Put a bitfield of length 1-32 bit into the buffer
 *
 * @param b the value to add, will be encoded in the bitfield
 * @param bits number of bits to use to encode b, e.g. 1 for boolean, 2, 3, etc.
 * @param packet_index the position in the packet (the index of the first byte to use)
 * @param bit_index the position in the byte (the index of the first bit to use)
 * @param buffer packet buffer to write into
 * @return new position of the last used byte in the buffer
 */
static inline uint8_t put_bitfield_n_by_index(int32_t b, uint8_t bits, uint8_t packet_index, uint8_t bit_index, uint8_t* r_bit_index, uint8_t* buffer)
{
    uint16_t bits_remain = bits;
    // Transform number into network order
    generic_32bit bin;
    generic_32bit bout;
    uint8_t i_bit_index, i_byte_index, curr_bits_n;
    bin.i = b;
    bout.b[0] = bin.b[3];
    bout.b[1] = bin.b[2];
    bout.b[2] = bin.b[1];
    bout.b[3] = bin.b[0];

    // buffer in
    // 01100000 01000000 00000000 11110001
    // buffer out
    // 11110001 00000000 01000000 01100000

    // Existing partly filled byte (four free slots)
    // 0111xxxx

    // Mask n free bits
    // 00001111 = 2^0 + 2^1 + 2^2 + 2^3 = 2^n - 1
    // = ((uint32_t)(1 << n)) - 1; // = 2^n - 1

    // Shift n bits into the right position
    // out = in >> n;

    // Mask and shift bytes
    i_bit_index = bit_index;
    i_byte_index = packet_index;
    if (bit_index > 0)
    {
        // If bits were available at start, they were available
        // in the byte before the current index
        i_byte_index--;
    }

    // While bits have not been packed yet
    while (bits_remain > 0)
    {
        // Bits still have to be packed
        // there can be more than 8 bits, so
        // we might have to pack them into more than one byte

        // First pack everything we can into the current 'open' byte
        //curr_bits_n = bits_remain << 3; // Equals  bits_remain mod 8
        //FIXME
        if (bits_remain <= (8 - i_bit_index))
        {
            // Enough space
            curr_bits_n = bits_remain;
        }
        else
        {
            curr_bits_n = (8 - i_bit_index);
        }
        
        // Pack these n bits into the current byte
        // Mask out whatever was at that position with ones (xxx11111)
        buffer[i_byte_index] &= (0xFF >> (8 - curr_bits_n));
        // Put content to this position, by masking out the non-used part
        buffer[i_byte_index] |= ((0x00 << curr_bits_n) & bout.i);
        
        // Increment the bit index
        i_bit_index += curr_bits_n;

        // Now proceed to the next byte, if necessary
        bits_remain -= curr_bits_n;
        if (bits_remain > 0)
        {
            // Offer another 8 bits / one byte
            i_byte_index++;
            i_bit_index = 0;
        }
    }
    
    *r_bit_index = i_bit_index;
    // If a partly filled byte is present, mark this as consumed
    if (i_bit_index != 7) i_byte_index++;
    return i_byte_index - packet_index;
}

#ifdef MAVLINK_USE_CONVENIENCE_FUNCTIONS

// To make MAVLink work on your MCU, define a similar function

/*

#include "mavlink_types.h"

void comm_send_ch(mavlink_channel_t chan, uint8_t ch)
{
    if (chan == MAVLINK_COMM_0)
    {
        uart0_transmit(ch);
    }
    if (chan == MAVLINK_COMM_1)
    {
        uart1_transmit(ch);
    }
}
 */

static inline void mavlink_send_uart_uint8_t(mavlink_channel_t chan, uint8_t b, uint16_t* checksum)
{
    crc_accumulate(b, checksum);
    comm_send_ch(chan, b);
}

static inline void mavlink_send_uart_int8_t(mavlink_channel_t chan, int8_t b, uint16_t* checksum)
{
    crc_accumulate(b, checksum);
    comm_send_ch(chan, b);
}

static inline void mavlink_send_uart_uint16_t(mavlink_channel_t chan, uint16_t b, uint16_t* checksum)
{
    char s;
    s = (b>>8)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b & 0xff);
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
}

static inline void mavlink_send_uart_int16_t(mavlink_channel_t chan, int16_t b, uint16_t* checksum)
{
    mavlink_send_uart_uint16_t(chan, b, checksum);
}

static inline void mavlink_send_uart_uint32_t(mavlink_channel_t chan, uint32_t b, uint16_t* checksum)
{
    char s;
    s = (b>>24)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b>>16)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b>>8)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b & 0xff);
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
}

static inline void mavlink_send_uart_int32_t(mavlink_channel_t chan, int32_t b, uint16_t* checksum)
{
    mavlink_send_uart_uint32_t(chan, b, checksum);
}

static inline void mavlink_send_uart_uint64_t(mavlink_channel_t chan, uint64_t b, uint16_t* checksum)
{
    char s;
    s = (b>>56)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b>>48)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b>>40)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b>>32)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b>>24)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b>>16)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b>>8)&0xff;
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
    s = (b & 0xff);
    comm_send_ch(chan, s);
    crc_accumulate(s, checksum);
}

static inline void mavlink_send_uart_int64_t(mavlink_channel_t chan, int64_t b, uint16_t* checksum)
{
    mavlink_send_uart_uint64_t(chan, b, checksum);
}

static inline void mavlink_send_uart_float(mavlink_channel_t chan, float b, uint16_t* checksum)
{
    generic_32bit g;
    g.f = b;
    mavlink_send_uart_uint32_t(chan, g.i, checksum);
}

static inline void mavlink_send_uart_double(mavlink_channel_t chan, double b, uint16_t* checksum)
{
    generic_64bit g;
    g.d = b;
    mavlink_send_uart_uint32_t(chan, g.ll, checksum);
}

static inline void mavlink_send_uart(mavlink_channel_t chan, mavlink_message_t* msg)
{
    // ARM7 MCU board implementation
    // Create pointer on message struct
    // Send STX
    comm_send_ch(chan, MAVLINK_STX);
    comm_send_ch(chan, msg->len);
    comm_send_ch(chan, msg->seq);
    comm_send_ch(chan, msg->sysid);
    comm_send_ch(chan, msg->compid);
    comm_send_ch(chan, msg->msgid);
    for(uint16_t i = 0; i < msg->len; i++)
    {
        comm_send_ch(chan, msg->payload[i]);
    }
    comm_send_ch(chan, msg->ck_a);
    comm_send_ch(chan, msg->ck_b);
}
#endif

#endif /* _MAVLINK_PROTOCOL_H_ */