MAVLink源檔案結構

MAVLink是為微型飛行器MAV（Micro Air Vehicle）設計的（LGPL）開源的通訊協定。是無人飛行器和地面站（Ground Control Station ，GCS）之間，以及無人飛行器之間通訊常用的協定。APM、PIXHAWK飛控，Mission Planner、QGroundControl地面站均使用了MAVLink協定進行通訊。

MAVLink--結構MAVLink源檔案結構mavlink消息包mavlink解析函數

common檔案夾：原始的MAVLink消息，包括各種消息的頭檔案
- common.h ：定義MAVLink各個消息包中用到的枚舉類型，各個消息包對應的CRC-EXTRA值、LENGTH值，包含（include）各個消息包的頭檔案
- 各個消息的頭檔案：
  - 1）定義消息内容對應的資料結構
  - 2）打包、發送消息的便捷函數
  - 3）消息包解析并擷取各個參數
autopilotmega，ASLUAV，pixhawk等檔案夾：包含各個飛控自定義的MAVLink消息類型
checksum.h：計算校驗碼的代碼
mavlink_conversions.h：dcm，歐拉角，四元數之間的轉換
mavlink_helper.h：提供各種便捷函數：
- 将各個消息包補充完整并發送。将資料載荷加上消息幀的頭部，如sysid和compid等，計算校驗碼，補充成為完整的mavlink消息包後發送；
- MAVLink消息包解析。
mavlink_types.h：定義用到的各種基本結構體（如mavlink_message_t）、枚舉類型（如

mavlink_param_union_t）

mavlink消息包

MAVLink--結構MAVLink源檔案結構mavlink消息包mavlink解析函數

　注：校驗（checksum）功能。加入MAVLINK_CRC_EXTRA，當兩個通訊終端之間（飛行器和地面站，或飛行器和飛行器）使用不同版本的MAVLink協定時，雙方計算得到的校驗碼會不同，則不同版本的MAVLink協定之間将無法通訊。

MAVLINK_MESSAGE_CRCS中存儲了每種消息包對應的MAVLINK_CRC_EXTRA。
這個MAVLINK_CRC_EXTRA在用python生成MAVLink代碼時在common.h頭檔案中自動生成。

mavlink解析函數

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) {
                    if(rxmsg->len > 0){
                        status->parse_state = MAVLINK_PARSE_STATE_GOT_MSGID3;
                    } else {
                        status->parse_state = MAVLINK_PARSE_STATE_GOT_PAYLOAD;
                    }
#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 |= ((uint32_t)c)<<16;
		mavlink_update_checksum(rxmsg, c);
		if(rxmsg->len > 0){
			status->parse_state = MAVLINK_PARSE_STATE_GOT_MSGID3;
		} else {
			status->parse_state = MAVLINK_PARSE_STATE_GOT_PAYLOAD;
		}
#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: {
		const mavlink_msg_entry_t *e = mavlink_get_msg_entry(rxmsg->msgid);
		uint8_t crc_extra = e?e->crc_extra:0;
		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;
		}
                rxmsg->ck[0] = c;

		// zero-fill the packet to cope with short incoming packets
                if (e && status->packet_idx < e->max_msg_len) {
                        memset(&_MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx], 0, e->max_msg_len - status->packet_idx);
		}
		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;
		}
		rxmsg->ck[1] = c;

		if (rxmsg->incompat_flags & MAVLINK_IFLAG_SIGNED) {
			status->parse_state = MAVLINK_PARSE_STATE_SIGNATURE_WAIT;
			status->signature_wait = MAVLINK_SIGNATURE_BLOCK_LEN;

			// If the CRC is already wrong, don't overwrite msg_received,
			// otherwise we can end up with garbage flagged as valid.
			if (status->msg_received != MAVLINK_FRAMING_BAD_CRC) {
				status->msg_received = MAVLINK_FRAMING_INCOMPLETE;
			}
		} else {
			if (status->signing &&
			   	(status->signing->accept_unsigned_callback == NULL ||
			   	 !status->signing->accept_unsigned_callback(status, rxmsg->msgid))) {

				// If the CRC is already wrong, don't overwrite msg_received.
				if (status->msg_received != MAVLINK_FRAMING_BAD_CRC) {
					status->msg_received = MAVLINK_FRAMING_BAD_SIGNATURE;
				}
			}
			status->parse_state = MAVLINK_PARSE_STATE_IDLE;
			if (r_message != NULL) {
				memcpy(r_message, rxmsg, sizeof(mavlink_message_t));
			}
		}
		break;
	case MAVLINK_PARSE_STATE_SIGNATURE_WAIT:
		rxmsg->signature[MAVLINK_SIGNATURE_BLOCK_LEN-status->signature_wait] = 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;
			if (r_message !=NULL) {
				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++;
	}

       if (r_message != NULL) {
           r_message->len = rxmsg->len; // Provide visibility on how far we are into current msg
       }
       if (r_mavlink_status != NULL) {	
           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
		 */
            if (r_message != NULL) {
                r_message->checksum = rxmsg->ck[0] | (rxmsg->ck[1]<<8);
            }
	}

	return status->msg_received;
}

此函數首先找到消息标志位

0xFE

，然後逐位元組的周遊，放入對應的

mavlink_message_t

結構體中，同時進行CRC檢查。

mavlink_status_t

結構體是檢測

mavlink_message_t

消息的結構體，存儲消息的狀态。

mavlink接收消息——統一指派到

mavlink_message_t

結構體中——然後通過encode代碼函數将各個變量成員提取——将變量成員指派給

mavlink_message_t

結構體——通過讀取真正的消息長度，将消息轉換成buffer——mavlink發送消息

mavlink協定關鍵檔案位：

MAVLink--結構MAVLink源檔案結構mavlink消息包mavlink解析函數

參考部落格：https://www.cnblogs.com/warrior1988/p/7729997.html

MAVLink--結構MAVLink源檔案結構mavlink消息包mavlink解析函數

MAVLink源檔案結構

mavlink消息包

mavlink解析函數

繼續閱讀

Apache (You don't have permission to access / on this server.）

debian9更新4.9.0核心到4.19.2核心過程

centOS7 配置 vsftpd 虛拟使用者及權限Vsftpd配置虛拟使用者及權限

linux-svn解除安裝與安裝

vsftp虛拟多使用者多權限一鍵部署腳本

Ubuntu14.04 LTS下安裝mongodb

httpd服務的部署、啟動、配置和簡單優化一、部署二、啟動三、配置檔案

配置網頁内容通路

手動安裝Intel network I217-LM網卡的Linux驅動

禁止ubuntu系統彈出報錯界面

Ubuntu Linux下Apache的配置檔案

samba伺服器的功能

【Linux】UDP廣播封包接收速率問題

Linux裝置模型（中）之上層容器

PowerPC平台 Linux移植三