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"
#include "mavlink_conversions.h"
#include <stdio.h>

#ifndef MAVLINK_HELPER
#define MAVLINK_HELPER
#endif

#include "mavlink_sha256.h"

/*
 * Internal function to give access to the channel status for each channel
 */
#ifndef MAVLINK_GET_CHANNEL_STATUS
MAVLINK_HELPER mavlink_status_t* mavlink_get_channel_status(uint8_t chan)
{
#ifdef MAVLINK_EXTERNAL_RX_STATUS
        // No m_mavlink_status array defined in function,
        // has to be defined externally
#else
        static mavlink_status_t m_mavlink_status[MAVLINK_COMM_NUM_BUFFERS];
#endif
        return &m_mavlink_status[chan];
}
#endif

/*
 * Internal function to give access to the channel buffer for each channel
 */
#ifndef MAVLINK_GET_CHANNEL_BUFFER
MAVLINK_HELPER mavlink_message_t* mavlink_get_channel_buffer(uint8_t chan)
{
        
#ifdef MAVLINK_EXTERNAL_RX_BUFFER
        // No m_mavlink_buffer array defined in function,
        // has to be defined externally
#else
        static mavlink_message_t m_mavlink_buffer[MAVLINK_COMM_NUM_BUFFERS];
#endif
        return &m_mavlink_buffer[chan];
}
#endif // MAVLINK_GET_CHANNEL_BUFFER

MAVLINK_HELPER void mavlink_reset_channel_status(uint8_t chan)
{
        mavlink_status_t *status = mavlink_get_channel_status(chan);
        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
}

MAVLINK_HELPER uint8_t mavlink_sign_packet(mavlink_signing_t *signing,
                                           uint8_t signature[MAVLINK_SIGNATURE_BLOCK_LEN],
                                           const uint8_t *header, uint8_t header_len,
                                           const uint8_t *packet, uint8_t packet_len,
                                           const uint8_t crc[2])
{
        mavlink_sha256_ctx ctx;
        union {
            uint64_t t64;
            uint8_t t8[8];
        } tstamp;
        if (signing == NULL || !(signing->flags & MAVLINK_SIGNING_FLAG_SIGN_OUTGOING)) {
            return 0;
        }
        signature[0] = signing->link_id;
        tstamp.t64 = signing->timestamp;
        memcpy(&signature[1], tstamp.t8, 6);
        signing->timestamp++;
        
        mavlink_sha256_init(&ctx);
        mavlink_sha256_update(&ctx, signing->secret_key, sizeof(signing->secret_key));
        mavlink_sha256_update(&ctx, header, header_len);
        mavlink_sha256_update(&ctx, packet, packet_len);
        mavlink_sha256_update(&ctx, crc, 2);
        mavlink_sha256_update(&ctx, signature, 7);
        mavlink_sha256_final_48(&ctx, &signature[7]);
        
        return MAVLINK_SIGNATURE_BLOCK_LEN;
}

MAVLINK_HELPER bool mavlink_signature_check(mavlink_signing_t *signing,
                                            mavlink_signing_streams_t *signing_streams,
                                            const mavlink_message_t *msg)
{
        if (signing == NULL) {
                return true;
        }
        const uint8_t *p = (const uint8_t *)&msg->magic;
        uint16_t len = MAVLINK_CORE_HEADER_LEN+1+msg->len+2+1+6;
        const uint8_t *psig = p + MAVLINK_CORE_HEADER_LEN+1+msg->len+2;
        const uint8_t *incoming_signature = psig+7;
        mavlink_sha256_ctx ctx;
        uint8_t signature[6];
        uint16_t i;
        
        mavlink_sha256_init(&ctx);
        mavlink_sha256_update(&ctx, signing->secret_key, sizeof(signing->secret_key));
        mavlink_sha256_update(&ctx, p, len);
        mavlink_sha256_final_48(&ctx, signature);
        if (memcmp(signature, incoming_signature, 6) != 0) {
                return false;
        }

        // now check timestamp
        union tstamp {
            uint64_t t64;
            uint8_t t8[8];
        } tstamp;
        uint8_t link_id = psig[0];
        tstamp.t64 = 0;
        memcpy(tstamp.t8, psig+1, 6);

        if (signing_streams == NULL) {
                return false;
        }
        
        // find stream
        for (i=0; i<signing_streams->num_signing_streams; i++) {
                if (msg->sysid == signing_streams->stream[i].sysid &&
                    msg->compid == signing_streams->stream[i].compid &&
                    link_id == signing_streams->stream[i].link_id) {
                        break;
                }
        }
        if (i == signing_streams->num_signing_streams) {
                if (signing_streams->num_signing_streams >= MAVLINK_MAX_SIGNING_STREAMS) {
                        // over max number of streams
                        return false;
                }
                // new stream. Only accept if timestamp is not more than 1 minute old
                if (tstamp.t64 + 6000*1000UL < signing->timestamp) {
                        return false;
                }
                // add new stream
                signing_streams->stream[i].sysid = msg->sysid;
                signing_streams->stream[i].compid = msg->compid;
                signing_streams->stream[i].link_id = link_id;
                signing_streams->num_signing_streams++;
        } else {
                union tstamp last_tstamp;
                last_tstamp.t64 = 0;
                memcpy(last_tstamp.t8, signing_streams->stream[i].timestamp_bytes, 6);
                if (tstamp.t64 <= last_tstamp.t64) {
                        // repeating old timestamp
                        return false;
                }
        }

        // remember last timestamp
        memcpy(signing_streams->stream[i].timestamp_bytes, psig+1, 6);

        // our next timestamp must be at least this timestamp
        if (tstamp.t64 > signing->timestamp) {
                signing->timestamp = tstamp.t64;
        }
        return true;
}


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 min_length, uint8_t length, uint8_t crc_extra)
{
        mavlink_status_t *status = mavlink_get_channel_status(chan);
        bool mavlink1 = (status->flags & MAVLINK_STATUS_FLAG_OUT_MAVLINK1) != 0;
        bool signing =  (!mavlink1) && status->signing && (status->signing->flags & MAVLINK_SIGNING_FLAG_SIGN_OUTGOING);
        uint8_t signature_len = signing? MAVLINK_SIGNATURE_BLOCK_LEN : 0;
        uint8_t header_len = MAVLINK_CORE_HEADER_LEN+1;
        uint8_t buf[MAVLINK_CORE_HEADER_LEN+1];
        if (mavlink1) {
                msg->magic = MAVLINK_STX_MAVLINK1;
                header_len = MAVLINK_CORE_HEADER_MAVLINK1_LEN+1;
        } else {
                msg->magic = MAVLINK_STX;
        }
        msg->len = mavlink1?min_length:length;
        msg->sysid = system_id;
        msg->compid = component_id;
        msg->incompat_flags = 0;
        if (signing) {
                msg->incompat_flags |= MAVLINK_IFLAG_SIGNED;
        }
        msg->compat_flags = 0;
        msg->seq = status->current_tx_seq;
        status->current_tx_seq = status->current_tx_seq + 1;

        // form the header as a byte array for the crc
        buf[0] = msg->magic;
        buf[1] = msg->len;
        if (mavlink1) {
                buf[2] = msg->seq;
                buf[3] = msg->sysid;
                buf[4] = msg->compid;
                buf[5] = msg->msgid & 0xFF;
        } else {
                buf[2] = msg->incompat_flags;
                buf[3] = msg->compat_flags;
                buf[4] = msg->seq;
                buf[5] = msg->sysid;
                buf[6] = msg->compid;
                buf[7] = msg->msgid & 0xFF;
                buf[8] = (msg->msgid >> 8) & 0xFF;
                buf[9] = (msg->msgid >> 16) & 0xFF;
        }
        
        msg->checksum = crc_calculate(&buf[1], header_len-1);
        crc_accumulate_buffer(&msg->checksum, _MAV_PAYLOAD(msg), msg->len);
        crc_accumulate(crc_extra, &msg->checksum);
        mavlink_ck_a(msg) = (uint8_t)(msg->checksum & 0xFF);
        mavlink_ck_b(msg) = (uint8_t)(msg->checksum >> 8);

        if (signing) {
                mavlink_sign_packet(status->signing,
                                    msg->signature,
                                    (const uint8_t *)buf, header_len,
                                    (const uint8_t *)_MAV_PAYLOAD(msg), msg->len,
                                    (const uint8_t *)_MAV_PAYLOAD(msg)+(uint16_t)msg->len);
        }
        
        return msg->len + header_len + 2 + signature_len;
}


MAVLINK_HELPER uint16_t mavlink_finalize_message(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id, 
                                                 uint8_t min_length, uint8_t length, uint8_t crc_extra)
{
    return mavlink_finalize_message_chan(msg, system_id, component_id, MAVLINK_COMM_0, min_length, length, crc_extra);
}

static inline void _mav_parse_error(mavlink_status_t *status)
{
    status->parse_error++;
}

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

MAVLINK_HELPER void _mav_finalize_message_chan_send(mavlink_channel_t chan, uint32_t msgid,
                                                    const char *packet, 
                                                    uint8_t min_length, uint8_t length, uint8_t crc_extra)
{
        uint16_t checksum;
        uint8_t buf[MAVLINK_NUM_HEADER_BYTES];
        uint8_t ck[2];
        mavlink_status_t *status = mavlink_get_channel_status(chan);
        uint8_t header_len = MAVLINK_CORE_HEADER_LEN;
        uint8_t signature_len = 0;
        uint8_t signature[MAVLINK_SIGNATURE_BLOCK_LEN];
        bool mavlink1 = (status->flags & MAVLINK_STATUS_FLAG_OUT_MAVLINK1) != 0;
        bool signing =  (!mavlink1) && status->signing && (status->signing->flags & MAVLINK_SIGNING_FLAG_SIGN_OUTGOING);

        if (mavlink1) {
            length = min_length;
            if (msgid > 255) {
                // can't send 16 bit messages
                _mav_parse_error(status);
                return;
            }
            header_len = MAVLINK_CORE_HEADER_MAVLINK1_LEN;
            buf[0] = MAVLINK_STX_MAVLINK1;
            buf[1] = length;
            buf[2] = status->current_tx_seq;
            buf[3] = mavlink_system.sysid;
            buf[4] = mavlink_system.compid;
            buf[5] = msgid & 0xFF;
        } else {
            uint8_t incompat_flags = 0;
            if (signing) {
                incompat_flags |= MAVLINK_IFLAG_SIGNED;
            }
            buf[0] = MAVLINK_STX;
            buf[1] = length;
            buf[2] = incompat_flags;
            buf[3] = 0; // compat_flags
            buf[4] = status->current_tx_seq;
            buf[5] = mavlink_system.sysid;
            buf[6] = mavlink_system.compid;
            buf[7] = msgid & 0xFF;
            buf[8] = (msgid >> 8) & 0xFF;
            buf[9] = (msgid >> 16) & 0xFF;
        }
        status->current_tx_seq++;
        checksum = crc_calculate((const uint8_t*)&buf[1], header_len);
        crc_accumulate_buffer(&checksum, packet, length);
        crc_accumulate(crc_extra, &checksum);
        ck[0] = (uint8_t)(checksum & 0xFF);
        ck[1] = (uint8_t)(checksum >> 8);

        if (signing) {
                // possibly add a signature
                signature_len = mavlink_sign_packet(status->signing, signature, buf, header_len+1,
                                                    (const uint8_t *)packet, length, ck);
        }
        
        MAVLINK_START_UART_SEND(chan, header_len + 3 + (uint16_t)length + (uint16_t)signature_len);
        _mavlink_send_uart(chan, (const char *)buf, header_len+1);
        _mavlink_send_uart(chan, packet, length);
        _mavlink_send_uart(chan, (const char *)ck, 2);
        if (signature_len != 0) {
                _mavlink_send_uart(chan, (const char *)signature, signature_len);
        }
        MAVLINK_END_UART_SEND(chan, header_len + 3 + (uint16_t)length + (uint16_t)signature_len);
}

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);
        // XXX use the right sequence here

        uint8_t header_len = MAVLINK_CORE_HEADER_LEN + 1;
        if (msg->magic == MAVLINK_STX_MAVLINK1) {
            header_len = MAVLINK_CORE_HEADER_MAVLINK1_LEN + 1;
        }
        MAVLINK_START_UART_SEND(chan, header_len + msg->len + 2);
        _mavlink_send_uart(chan, (const char *)&msg->magic, header_len);
        _mavlink_send_uart(chan, _MAV_PAYLOAD(msg), msg->len);
        _mavlink_send_uart(chan, (const char *)ck, 2);
        MAVLINK_END_UART_SEND(chan, header_len + msg->len + 2);
}
#endif // MAVLINK_USE_CONVENIENCE_FUNCTIONS

MAVLINK_HELPER uint16_t mavlink_msg_to_send_buffer(uint8_t *buf, const mavlink_message_t *msg)
{
        uint8_t signature_len, header_len;
        uint8_t *ck;
        
        if (msg->magic == MAVLINK_STX_MAVLINK1) {
                signature_len = 0;
                header_len = MAVLINK_CORE_HEADER_MAVLINK1_LEN;
                buf[0] = msg->magic;
                buf[1] = msg->len;
                buf[2] = msg->seq;
                buf[3] = msg->sysid;
                buf[4] = msg->compid;
                buf[5] = msg->msgid & 0xFF;
                memcpy(&buf[6], _MAV_PAYLOAD(msg), msg->len);
                ck = buf + header_len + 1 + (uint16_t)msg->len;
        } else {
                header_len = MAVLINK_CORE_HEADER_LEN;
                buf[0] = msg->magic;
                buf[1] = msg->len;
                buf[2] = msg->incompat_flags;
                buf[3] = msg->compat_flags;
                buf[4] = msg->seq;
                buf[5] = msg->sysid;
                buf[6] = msg->compid;
                buf[7] = msg->msgid & 0xFF;
                buf[8] = (msg->msgid >> 8) & 0xFF;
                buf[9] = (msg->msgid >> 16) & 0xFF;
                memcpy(&buf[10], _MAV_PAYLOAD(msg), msg->len);
                ck = buf + header_len + 1 + (uint16_t)msg->len;
                signature_len = (msg->incompat_flags & MAVLINK_IFLAG_SIGNED)?MAVLINK_SIGNATURE_BLOCK_LEN:0;
        }
        ck[0] = (uint8_t)(msg->checksum & 0xFF);
        ck[1] = (uint8_t)(msg->checksum >> 8);
        if (signature_len > 0) {
                memcpy(&ck[2], msg->signature, signature_len);
        }

        return header_len + 1 + 2 + (uint16_t)msg->len + (uint16_t)signature_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);
}

/*
  return the crc_entry value for a msgid
*/
MAVLINK_HELPER const mavlink_msg_entry_t *mavlink_get_msg_entry(uint32_t msgid)
{
        static const mavlink_msg_entry_t mavlink_message_crcs[] = MAVLINK_MESSAGE_CRCS;
        /*
          use a bisection search to find the right entry. A perfect hash may be better
          Note that this assumes the table is sorted by msgid
        */
        uint32_t low=0, high=sizeof(mavlink_message_crcs)/sizeof(mavlink_message_crcs[0]);
        while (low < high) {
            uint32_t mid = (low+1+high)/2;
            if (msgid < mavlink_message_crcs[mid].msgid) {
                high = mid-1;
                continue;
            }
            if (msgid > mavlink_message_crcs[mid].msgid) {
                low = mid;
                continue;
            }
            low = mid;
            break;
        }
        if (mavlink_message_crcs[low].msgid != msgid) {
            // msgid is not in the table
            return NULL;
        }
        return &mavlink_message_crcs[low];
}

/*
  return the crc_extra value for a message
*/
MAVLINK_HELPER uint8_t mavlink_get_crc_extra(const mavlink_message_t *msg)
{
        const mavlink_msg_entry_t *e = mavlink_get_msg_entry(msg->msgid);
        return e?e->crc_extra:0;
}

/*
  return the expected message length
*/
#define MAVLINK_HAVE_EXPECTED_MESSAGE_LENGTH
MAVLINK_HELPER uint8_t mavlink_expected_message_length(const mavlink_message_t *msg)
{
        const mavlink_msg_entry_t *e = mavlink_get_msg_entry(msg->msgid);
        return e?e->msg_len:0;
}

MAVLINK_HELPER uint8_t mavlink_frame_char_buffer(mavlink_message_t* rxmsg, 
                                                 mavlink_status_t* status,
                                                 uint8_t c, 
                                                 mavlink_message_t* r_message, 
                                                 mavlink_status_t* r_mavlink_status)
{
        /* 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.
        */
#ifdef 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

        int bufferIndex = 0;

        status->msg_received = MAVLINK_FRAMING_INCOMPLETE;

        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;
                        status->flags &= ~MAVLINK_STATUS_FLAG_IN_MAVLINK1;
                        mavlink_start_checksum(rxmsg);
                } else if (c == MAVLINK_STX_MAVLINK1)
                {
                        status->parse_state = MAVLINK_PARSE_STATE_GOT_STX;
                        rxmsg->len = 0;
                        rxmsg->magic = c;
                        status->flags |= MAVLINK_STATUS_FLAG_IN_MAVLINK1;
                        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++;
                        _mav_parse_error(status);
                        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);
                        if (status->flags & MAVLINK_STATUS_FLAG_IN_MAVLINK1) {
                            rxmsg->incompat_flags = 0;
                            rxmsg->compat_flags = 0;
                            status->parse_state = MAVLINK_PARSE_STATE_GOT_COMPAT_FLAGS;
                        } else {
                            status->parse_state = MAVLINK_PARSE_STATE_GOT_LENGTH;
                        }
                }
                break;

        case MAVLINK_PARSE_STATE_GOT_LENGTH:
                rxmsg->incompat_flags = c;
                if ((rxmsg->incompat_flags & ~MAVLINK_IFLAG_MASK) != 0) {
                        // message includes an incompatible feature flag
                        _mav_parse_error(status);
                        status->msg_received = 0;
                        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
                        break;
                }
                mavlink_update_checksum(rxmsg, c);
                status->parse_state = MAVLINK_PARSE_STATE_GOT_INCOMPAT_FLAGS;
                break;

        case MAVLINK_PARSE_STATE_GOT_INCOMPAT_FLAGS:
                rxmsg->compat_flags = c;
                mavlink_update_checksum(rxmsg, c);
                status->parse_state = MAVLINK_PARSE_STATE_GOT_COMPAT_FLAGS;
                break;

        case MAVLINK_PARSE_STATE_GOT_COMPAT_FLAGS:
                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 (status->flags & MAVLINK_STATUS_FLAG_IN_MAVLINK1) {
                    status->parse_state = MAVLINK_PARSE_STATE_GOT_MSGID3;
#ifdef MAVLINK_CHECK_MESSAGE_LENGTH
                    if (rxmsg->len != MAVLINK_MESSAGE_LENGTH(rxmsg->msgid))
                    {
                        _mav_parse_error(status);
                        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
                        break;
                    }
#endif
                } else {
                    status->parse_state = MAVLINK_PARSE_STATE_GOT_MSGID1;
                }
                break;

        case MAVLINK_PARSE_STATE_GOT_MSGID1:
                rxmsg->msgid |= c<<8;
                mavlink_update_checksum(rxmsg, c);
                status->parse_state = MAVLINK_PARSE_STATE_GOT_MSGID2;
                break;

        case MAVLINK_PARSE_STATE_GOT_MSGID2:
                rxmsg->msgid |= c<<16;
                mavlink_update_checksum(rxmsg, c);
                status->parse_state = MAVLINK_PARSE_STATE_GOT_MSGID3;
#ifdef MAVLINK_CHECK_MESSAGE_LENGTH
                if (rxmsg->len != MAVLINK_MESSAGE_LENGTH(rxmsg->msgid))
                {
                        _mav_parse_error(status);
                        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
                        break;
                }
#endif
                break;
                
        case MAVLINK_PARSE_STATE_GOT_MSGID3:
                _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: {
                uint8_t crc_extra = mavlink_get_crc_extra(rxmsg);
                mavlink_update_checksum(rxmsg, crc_extra);
                if (c != (rxmsg->checksum & 0xFF)) {
                        status->parse_state = MAVLINK_PARSE_STATE_GOT_BAD_CRC1;
                } 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:
        case MAVLINK_PARSE_STATE_GOT_BAD_CRC1:
                if (status->parse_state == MAVLINK_PARSE_STATE_GOT_BAD_CRC1 || c != (rxmsg->checksum >> 8)) {
                        // got a bad CRC message
                        status->msg_received = MAVLINK_FRAMING_BAD_CRC;
                } else {
                        // Successfully got message
                        status->msg_received = MAVLINK_FRAMING_OK;
                }
                _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx+1] = (char)c;
                if (rxmsg->incompat_flags & MAVLINK_IFLAG_SIGNED) {
                        status->parse_state = MAVLINK_PARSE_STATE_SIGNATURE_WAIT;
                        status->signature_wait = MAVLINK_SIGNATURE_BLOCK_LEN;
                        status->msg_received = MAVLINK_FRAMING_INCOMPLETE;
                } else {
                        if (status->signing &&
                            (status->signing->accept_unsigned_callback == NULL ||
                             !status->signing->accept_unsigned_callback(status, rxmsg->msgid))) {
                                // don't accept this unsigned packet
                                status->msg_received = MAVLINK_FRAMING_BAD_SIGNATURE;
                        }
                        status->parse_state = MAVLINK_PARSE_STATE_IDLE;
                        memcpy(r_message, rxmsg, sizeof(mavlink_message_t));
                }
                break;
        case MAVLINK_PARSE_STATE_SIGNATURE_WAIT:
                _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx+2+(MAVLINK_SIGNATURE_BLOCK_LEN-status->signature_wait)] = (char)c;
                status->signature_wait--;
                if (status->signature_wait == 0) {
                        // we have the whole signature, check it is OK
                        bool sig_ok = mavlink_signature_check(status->signing, status->signing_streams, rxmsg);
                        if (!sig_ok &&
                            (status->signing->accept_unsigned_callback &&
                             status->signing->accept_unsigned_callback(status, rxmsg->msgid))) {
                                // accepted via application level override
                                sig_ok = true;
                        }
                        if (sig_ok) {
                                status->msg_received = MAVLINK_FRAMING_OK;
                        } else {
                                status->msg_received = MAVLINK_FRAMING_BAD_SIGNATURE;
                        }
                        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 == MAVLINK_FRAMING_OK)
        {
                //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;
        r_mavlink_status->flags = status->flags;
        status->parse_error = 0;

        if (status->msg_received == MAVLINK_FRAMING_BAD_CRC) {
                /*
                  the CRC came out wrong. We now need to overwrite the
                  msg CRC with the one on the wire so that if the
                  caller decides to forward the message anyway that
                  mavlink_msg_to_send_buffer() won't overwrite the
                  checksum
                 */
                r_message->checksum = _MAV_PAYLOAD(rxmsg)[status->packet_idx] | (_MAV_PAYLOAD(rxmsg)[status->packet_idx+1]<<8);
        }

        return status->msg_received;
}

MAVLINK_HELPER uint8_t mavlink_frame_char(uint8_t chan, uint8_t c, mavlink_message_t* r_message, mavlink_status_t* r_mavlink_status)
{
        return mavlink_frame_char_buffer(mavlink_get_channel_buffer(chan),
                                         mavlink_get_channel_status(chan),
                                         c,
                                         r_message,
                                         r_mavlink_status);
}


MAVLINK_HELPER uint8_t mavlink_parse_char(uint8_t chan, uint8_t c, mavlink_message_t* r_message, mavlink_status_t* r_mavlink_status)
{
    uint8_t msg_received = mavlink_frame_char(chan, c, r_message, r_mavlink_status);
    if (msg_received == MAVLINK_FRAMING_BAD_CRC ||
        msg_received == MAVLINK_FRAMING_BAD_SIGNATURE) {
            // we got a bad CRC. Treat as a parse failure
            mavlink_message_t* rxmsg = mavlink_get_channel_buffer(chan);
            mavlink_status_t* status = mavlink_get_channel_status(chan);
            _mav_parse_error(status);
            status->msg_received = MAVLINK_FRAMING_INCOMPLETE;
            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);
            }
            return 0;
    }
    return 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, (const 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_ */