mavlink_helpers.h

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#ifndef  _MAVLINK_HELPERS_H_
#define  _MAVLINK_HELPERS_H_

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

#ifndef MAVLINK_HELPER
#define MAVLINK_HELPER
#endif

/*
  internal function to give access to the channel status for each channel
 */
MAVLINK_HELPER 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];
}

/*
 internal function to give access to the channel buffer for each channel
 */
MAVLINK_HELPER mavlink_message_t* mavlink_get_channel_buffer(uint8_t chan)
{
        
#if MAVLINK_EXTERNAL_RX_BUFFER
        // No m_mavlink_message array defined in function,
        // has to be defined externally
#ifndef m_mavlink_message
#error ERROR: IF #define MAVLINK_EXTERNAL_RX_BUFFER IS SET, THE BUFFER HAS TO BE ALLOCATED OUTSIDE OF THIS FUNCTION (mavlink_message_t m_mavlink_buffer[MAVLINK_COMM_NUM_BUFFERS];)
#endif
#else
        static mavlink_message_t m_mavlink_buffer[MAVLINK_COMM_NUM_BUFFERS];
#endif
        return &m_mavlink_buffer[chan];
}

#if MAVLINK_CRC_EXTRA
MAVLINK_HELPER uint16_t mavlink_finalize_message_chan(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id, 
                                                      uint8_t chan, uint8_t length, uint8_t crc_extra)
#else
MAVLINK_HELPER uint16_t mavlink_finalize_message_chan(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id, 
                                                      uint8_t chan, uint8_t length)
#endif
{
        // This code part is the same for all messages;
        uint16_t checksum;
        msg->magic = MAVLINK_STX;
        msg->len = length;
        msg->sysid = system_id;
        msg->compid = component_id;
        // One sequence number per channel
        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*)&msg->len, length + MAVLINK_CORE_HEADER_LEN);
#if MAVLINK_CRC_EXTRA
        crc_accumulate(crc_extra, &checksum);
#endif
        mavlink_ck_a(msg) = (uint8_t)(checksum & 0xFF);
        mavlink_ck_b(msg) = (uint8_t)(checksum >> 8);

        return length + MAVLINK_NUM_NON_PAYLOAD_BYTES;
}


#if MAVLINK_CRC_EXTRA
MAVLINK_HELPER uint16_t mavlink_finalize_message(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id, 
                                                 uint8_t length, uint8_t crc_extra)
{
        return mavlink_finalize_message_chan(msg, system_id, component_id, MAVLINK_COMM_0, length, crc_extra);
}
#else
MAVLINK_HELPER uint16_t mavlink_finalize_message(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id, 
                                                 uint8_t length)
{
        return mavlink_finalize_message_chan(msg, system_id, component_id, MAVLINK_COMM_0, length);
}
#endif

#ifdef MAVLINK_USE_CONVENIENCE_FUNCTIONS
MAVLINK_HELPER void _mavlink_send_uart(mavlink_channel_t chan, const char *buf, uint16_t len);

#if MAVLINK_CRC_EXTRA
MAVLINK_HELPER void _mav_finalize_message_chan_send(mavlink_channel_t chan, uint8_t msgid, const char *packet, 
                                                    uint8_t length, uint8_t crc_extra)
#else
MAVLINK_HELPER void _mav_finalize_message_chan_send(mavlink_channel_t chan, uint8_t msgid, const char *packet, uint8_t length)
#endif
{
        uint16_t checksum;
        uint8_t buf[MAVLINK_NUM_HEADER_BYTES];
        uint8_t ck[2];
        mavlink_status_t *status = mavlink_get_channel_status(chan);
        buf[0] = MAVLINK_STX;
        buf[1] = length;
        buf[2] = status->current_tx_seq;
        buf[3] = mavlink_system.sysid;
        buf[4] = mavlink_system.compid;
        buf[5] = msgid;
        status->current_tx_seq++;
        checksum = crc_calculate((uint8_t*)&buf[1], MAVLINK_CORE_HEADER_LEN);
        crc_accumulate_buffer(&checksum, packet, length);
#if MAVLINK_CRC_EXTRA
        crc_accumulate(crc_extra, &checksum);
#endif
        ck[0] = (uint8_t)(checksum & 0xFF);
        ck[1] = (uint8_t)(checksum >> 8);

        MAVLINK_START_UART_SEND(chan, MAVLINK_NUM_NON_PAYLOAD_BYTES + (uint16_t)length);
        _mavlink_send_uart(chan, (const char *)buf, MAVLINK_NUM_HEADER_BYTES);
        _mavlink_send_uart(chan, packet, length);
        _mavlink_send_uart(chan, (const char *)ck, 2);
        MAVLINK_END_UART_SEND(chan, MAVLINK_NUM_NON_PAYLOAD_BYTES + (uint16_t)length);
}

MAVLINK_HELPER void _mavlink_resend_uart(mavlink_channel_t chan, const mavlink_message_t *msg)
{
        uint8_t ck[2];

        ck[0] = (uint8_t)(msg->checksum & 0xFF);
        ck[1] = (uint8_t)(msg->checksum >> 8);

        MAVLINK_START_UART_SEND(chan, MAVLINK_NUM_NON_PAYLOAD_BYTES + msg->len);
        _mavlink_send_uart(chan, (const char *)&msg->magic, MAVLINK_NUM_HEADER_BYTES);
        _mavlink_send_uart(chan, _MAV_PAYLOAD(msg), msg->len);
        _mavlink_send_uart(chan, (const char *)ck, 2);
        MAVLINK_END_UART_SEND(chan, MAVLINK_NUM_NON_PAYLOAD_BYTES + msg->len);
}
#endif // MAVLINK_USE_CONVENIENCE_FUNCTIONS

MAVLINK_HELPER uint16_t mavlink_msg_to_send_buffer(uint8_t *buffer, const mavlink_message_t *msg)
{
        memcpy(buffer, (const uint8_t *)&msg->magic, MAVLINK_NUM_NON_PAYLOAD_BYTES + (uint16_t)msg->len);
        return MAVLINK_NUM_NON_PAYLOAD_BYTES + (uint16_t)msg->len;
}

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


MAVLINK_HELPER void mavlink_start_checksum(mavlink_message_t* msg)
{
        crc_init(&msg->checksum);
}

MAVLINK_HELPER void mavlink_update_checksum(mavlink_message_t* msg, uint8_t c)
{
        crc_accumulate(c, &msg->checksum);
}

MAVLINK_HELPER uint8_t mavlink_parse_char(uint8_t chan, uint8_t c, mavlink_message_t* r_message, mavlink_status_t* r_mavlink_status)
{
        /*
          default message crc function. You can override this per-system to
          put this data in a different memory segment
        */
#if MAVLINK_CRC_EXTRA
#ifndef MAVLINK_MESSAGE_CRC
        static const uint8_t mavlink_message_crcs[256] = MAVLINK_MESSAGE_CRCS;
#define MAVLINK_MESSAGE_CRC(msgid) mavlink_message_crcs[msgid]
#endif
#endif


/* Enable this option to check the length of each message.
This allows invalid messages to be caught much sooner. Use if the transmission
medium is prone to missing (or extra) characters (e.g. a radio that fades in
and out). Only use if the channel will only contain messages types listed in
the headers.
*/
#if MAVLINK_CHECK_MESSAGE_LENGTH
#ifndef MAVLINK_MESSAGE_LENGTH
        static const uint8_t mavlink_message_lengths[256] = MAVLINK_MESSAGE_LENGTHS;
#define MAVLINK_MESSAGE_LENGTH(msgid) mavlink_message_lengths[msgid]
#endif
#endif

        mavlink_message_t* rxmsg = mavlink_get_channel_buffer(chan); 
        mavlink_status_t* status = mavlink_get_channel_status(chan); 
        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;
                        rxmsg->len = 0;
                        rxmsg->magic = c;
                        mavlink_start_checksum(rxmsg);
                }
                break;

        case MAVLINK_PARSE_STATE_GOT_STX:
                        if (status->msg_received 
/* Support shorter buffers than the
   default maximum packet size */
#if (MAVLINK_MAX_PAYLOAD_LEN < 255)
                                || c > MAVLINK_MAX_PAYLOAD_LEN
#endif
                                )
                {
                        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:
#if MAVLINK_CHECK_MESSAGE_LENGTH
                if (rxmsg->len != MAVLINK_MESSAGE_LENGTH(c))
                {
                        status->parse_error++;
                        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
                        break;
            }
#endif
                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:
                _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx++] = (char)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 MAVLINK_CRC_EXTRA
                mavlink_update_checksum(rxmsg, MAVLINK_MESSAGE_CRC(rxmsg->msgid));
#endif
                if (c != (rxmsg->checksum & 0xFF)) {
                        // 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;
                                rxmsg->len = 0;
                                mavlink_start_checksum(rxmsg);
                        }
                }
                else
                {
                        status->parse_state = MAVLINK_PARSE_STATE_GOT_CRC1;
                        _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx] = (char)c;
                }
                break;

        case MAVLINK_PARSE_STATE_GOT_CRC1:
                if (c != (rxmsg->checksum >> 8)) {
                        // 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;
                                rxmsg->len = 0;
                                mavlink_start_checksum(rxmsg);
                        }
                }
                else
                {
                        // Successfully got message
                        status->msg_received = 1;
                        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
                        _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx+1] = (char)c;
                        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_message->len = rxmsg->len; // Provide visibility on how far we are into current msg
        r_mavlink_status->parse_state = status->parse_state;
        r_mavlink_status->packet_idx = status->packet_idx;
        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;
}

MAVLINK_HELPER 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
        int32_t v;
        uint8_t i_bit_index, i_byte_index, curr_bits_n;
#if MAVLINK_NEED_BYTE_SWAP
        union {
                int32_t i;
                uint8_t b[4];
        } bin, bout;
        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];
        v = bout.i;
#else
        v = b;
#endif

        // 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 <= (uint8_t)(8 - i_bit_index))
                {
                        // Enough space
                        curr_bits_n = (uint8_t)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) & v);
                
                // 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 comm_send_ch() if you wish
// to send 1 byte at a time, or MAVLINK_SEND_UART_BYTES() to send a
// whole packet at a time

/*

#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);
    }
}
 */

MAVLINK_HELPER void _mavlink_send_uart(mavlink_channel_t chan, const char *buf, uint16_t len)
{
#ifdef MAVLINK_SEND_UART_BYTES
        /* this is the more efficient approach, if the platform
           defines it */
        MAVLINK_SEND_UART_BYTES(chan, (uint8_t *)buf, len);
#else
        /* fallback to one byte at a time */
        uint16_t i;
        for (i = 0; i < len; i++) {
                comm_send_ch(chan, (uint8_t)buf[i]);
        }
#endif
}
#endif // MAVLINK_USE_CONVENIENCE_FUNCTIONS

#endif /* _MAVLINK_HELPERS_H_ */