【无人机学习之DroidPlanner】MAVLink协议

█ 【无人机学习之DroidPlanner】MAVLink协议

█ 系列文章目录

提示：这里是收集了无人机的相关文章

• 【无人机学习】无人机基础知识
• 【无人机学习】Mission Planner（pc端）和QGroundControl（android端）
• 【无人机学习之DroidPlanner】MAVLink协议
• 【无人机学习之DroidPlanner】msg_heartbeat心跳处理
• 【无人机学习之DroidPlanner】msg_sys_status系统状态
• 【无人机学习之QGroundControl】android端App初解1
• 【无人机学习之QGroundControl】android端App初解2-APMPowerComponent（含QML的介绍）
• 【无人机学习之QGroundControl】android端App初解3-ParameterEditorController

█ 文章目录

• █ 【无人机学习之DroidPlanner】MAVLink协议
• █ 系列文章目录
• █ 文章目录
• █ 读前说明
• █ MAVLink
• • 1.简介
  • 2.协议格式
  • 3.使用Python写的用于生成C、Java等语言的MavLink生成器软件：
• █ DroidPlanner怎么发送消息（mavlink v1.0）
• • 1.mavlink 版本
  • 2.代码过程
  • 3.配置起飞模式（MavLinkCommands.java）
  • 4.发送（MAVLinkClient.java）
  • 5.发送（MavLinkConnection.java）
  • 6.MAVLink协议
  • 7.其他
• █ 相关资料
• █ 免责声明

█ 读前说明

• 本文通过学习别人写demo,学习一些课件,参考一些博客,学习相关知识，如有涉及侵权请告知

• 本文可能只简单罗列了一些相关的代码实现过程，复制了一些大神的高论，如内容有误请自行辨别

• 涉及到的逻辑以及说明可能只做了简单的介绍，主要当做笔记，了解过程而已，如有不同看法，欢迎下方评论

• 本文源码：DroidPlanner/Tower　
  dronekit/dronekit-android

• MAVLink定义：
  MAVLink - common - msg_attitude　
  MissionPlanner-master2021 - Mavlink.cs

█ MAVLink

1.简介

• 官网：MAVLink
• MAVLink是一种非常轻量级的通信协议，主要是用于无人机上，还有无人车等；
• 目前MAVLink有两个版本：V1.0（2013年发布）和V2.0版本（2017年发布）；
• V2是V1的拓展版本，简化传输，向下兼容Ｖ1.0，是一个更加安全和可扩展的协议；
• MAVLink通信内容包含常见通信协议帧头、帧尾、长度、校验等。
• MAVLink目前最新版本是 V 2.3；
• qgc地面站使用的是mavlink ，和px4是同一个人研发的；

2.协议格式

官网：mavlink协议格式
比较重要的字段是msgid和payload，msgid用来区分消息类型，判断需要转换成什么类型的对话，payload是对应的值

uint8_t magic;              ///< protocol magic marker
uint8_t len;                ///< Length of payload
uint8_t incompat_flags;     ///< flags that must be understood （V2.0增加）
uint8_t compat_flags;       ///< flags that can be ignored if not understood（V2.0增加）
uint8_t seq;                ///< Sequence of packet
uint8_t sysid;              ///< ID of message sender system/aircraft
uint8_t compid;             ///< ID of the message sender component
uint8_t msgid 0:7;          ///< first 8 bits of the ID of the message
uint8_t msgid 8:15;         ///< middle 8 bits of the ID of the message
uint8_t msgid 16:23;        ///< last 8 bits of the ID of the message
uint8_t payload[max 255];   ///< A maximum of 255 payload bytes
uint16_t checksum;          ///< CRC-16/MCRF4XX
uint8_t signature[13];      ///< Signature which allows ensuring that the link is tamper-proof (optional)（V2.0增加）

3.使用Python写的用于生成C、Java等语言的MavLink生成器软件：

• https://github.com/mavlink/mavlink

█ DroidPlanner怎么发送消息（mavlink v1.0）

1.mavlink 版本

从代码中可以看出：
使用的mavlink的版本是v1.0；
其实比V2.0少了INC FLAGS、CMP FLAGS、SIGNATURE 三个参数；

2.代码过程

3.配置起飞模式（MavLinkCommands.java）

提示：此文件全路径为：org.droidplanner.services.android.impl.core.MAVLink.MavLinkCommands.java

• 首先看下这份代码的1个发送命令方法：(配置起飞模式)

public static void sendTakeoff(MavLinkDrone drone, double alt, ICommandListener listener) {msg_command_long msg = new msg_command_long();//  msgid = 76; msg.target_system = drone.getSysid();msg.target_component = drone.getCompid();msg.command = MAV_CMD.MAV_CMD_NAV_TAKEOFF;// 起飞模式msg.param7 = (float) alt;// z轴，即高度drone.getMavClient().sendMessage(msg, listener);// 下一步需要查看的信息：MAVLinkClient.sendMessage()
}

• new msg_command_long()就是创建了一个 msgid = MAVLINK_MSG_ID_COMMAND_LONG;即76；
• 查看#76的协议文档：
  提示：注意到command的数据类型是MAV_CMD
  
• 查看MAV_CMD的协议文档：
  MAVLink Commands (MAV_CMD)
  MAVLink命令（MAV_CMD）和消息不同，定义了最多7个参数的值，被打包在特定任务中使用的协议和命令协议的消息。命令执行的飞行器
  MAV_CMD_NAV_TAKEOFF：（22 起飞模式）
  
  

4.发送（MAVLinkClient.java）

提示：此文件全路径为：org.droidplanner.services.android.impl.communication.service.MAVLinkClient.java

    private static final int DEFAULT_SYS_ID = 255;private static final int DEFAULT_COMP_ID = 190;

 @Overridepublic synchronized void sendMessage(MAVLinkMessage message, ICommandListener listener) {sendMavMessage(message, DEFAULT_SYS_ID, DEFAULT_COMP_ID, listener);}

    protected void sendMavMessage(MAVLinkMessage message, int sysId, int compId, ICommandListener listener){if (isDisconnected() || message == null) {return;}final MAVLinkPacket packet = message.pack();packet.sysid = sysId;packet.compid = compId;packet.seq = packetSeqNumber;mavlinkConn.sendMavPacket(packet);// 下一步需要查看的信息：MavLinkConnectionpacketSeqNumber = (packetSeqNumber + 1) % (MAX_PACKET_SEQUENCE + 1);if (commandTracker != null && listener != null) {commandTracker.onCommandSubmitted(message, listener);}}

5.发送（MavLinkConnection.java）

提示：此文件全路径为：org.droidplanner.services.android.impl.core.MAVLink.connection.MavLinkConnection.java

	// 转换成16进制大写字符串发送出去public void sendMavPacket(MAVLinkPacket packet) {final byte[] packetData = packet.encodePacket();Log.e("sendMavPacket", String2ByteArrayUtils.INSTANCE.bytes2Hex(packetData));if (!mPacketsToSend.offer(packetData)) {mLogger.logErr(TAG, "Unable to send mavlink packet. Packet queue is full!");}}

6.MAVLink协议

提示：
每个数基本上都是一个字节(uint8_t )即0x00-0xff;
msg_command_long 的发送结构
| STX | LEN|SEQ|SYS ID|COMPID ID|MSG ID|PLAYLOAD|CHECK SUM|
|–|–|–|–|–|–|–|–|–|
|起始位|载荷长度|包序号|地面站系统ID|地面站部件 ID|消息ID|载荷|校验|
|固定值|自动|自动|固定值|固定值|COMMAND LONG|–|自动|
|0xFE|–|–|255|190|76|–|–|

PLAYLOAD的发送结构(MAV_CMD_NAV_TAKEOFF)

7.其他

1.MissionPlanner 使用的是 MAVLink 2.0（参考 “MissionPlanner-master\ExtLibs\Mavlink\Mavlink.cs”）

public partial class MAVLink
{public const string MAVLINK_BUILD_DATE = "Sat Dec 26 2020";public const string MAVLINK_WIRE_PROTOCOL_VERSION = "2.0";// ###V2.0标记public const int MAVLINK_MAX_PAYLOAD_LEN = 255;public const byte MAVLINK_CORE_HEADER_LEN = 9;///< Length of core header (of the comm. layer)public const byte MAVLINK_CORE_HEADER_MAVLINK1_LEN = 5;///< Length of MAVLink1 core header (of the comm. layer)public const byte MAVLINK_NUM_HEADER_BYTES = (MAVLINK_CORE_HEADER_LEN + 1);///< Length of all header bytes, including core and stxpublic const byte MAVLINK_NUM_CHECKSUM_BYTES = 2;public const byte MAVLINK_NUM_NON_PAYLOAD_BYTES = (MAVLINK_NUM_HEADER_BYTES + MAVLINK_NUM_CHECKSUM_BYTES);public const byte MAVLINK_STX_MAVLINK1 = 0xFE;// ###V2.0标记,V1.0是0xFD。。。。。。// msgid, name, crc, minlength, length, typepublic static message_info[] MAVLINK_MESSAGE_INFOS = new message_info[] {new message_info(148, "AUTOPILOT_VERSION", 178, 60, 78, typeof( mavlink_autopilot_version_t )),new message_info(42001, "ICAROUS_KINEMATIC_BANDS", 239, 46, 46, typeof( mavlink_icarous_kinematic_bands_t )),new message_info(269, "VIDEO_STREAM_INFORMATION", 58, 246, 246, typeof( mavlink_video_stream_information_t )),new message_info(0, "HEARTBEAT", 50, 9, 9, typeof( mavlink_heartbeat_t )),};public const byte MAVLINK_VERSION = 2;public const byte MAVLINK_IFLAG_SIGNED=  0x01;public const byte MAVLINK_IFLAG_MASK   = 0x01;public struct message_info{public uint msgid { get; internal set; }public string name { get; internal set; }public byte crc { get; internal set; }public uint minlength { get; internal set; }public uint length { get; internal set; }public Type type { get; internal set; }}public struct mavlink_autopilot_version_t{public mavlink_autopilot_version_t(/*MAV_PROTOCOL_CAPABILITY*/ulong capabilities,ulong uid,uint flight_sw_version,uint middleware_sw_version,uint os_sw_version,uint board_version,ushort vendor_id,ushort product_id,byte[] flight_custom_version,byte[] middleware_custom_version,byte[] os_custom_version,byte[] uid2) {this.capabilities = capabilities;this.uid = uid;this.flight_sw_version = flight_sw_version;this.middleware_sw_version = middleware_sw_version;this.os_sw_version = os_sw_version;this.board_version = board_version;this.vendor_id = vendor_id;this.product_id = product_id;this.flight_custom_version = flight_custom_version;this.middleware_custom_version = middleware_custom_version;this.os_custom_version = os_custom_version;this.uid2 = uid2;}/// 
Bitmap of capabilities MAV_PROTOCOL_CAPABILITY  bitmask[Units("")][Description("Bitmap of capabilities")]public  /*MAV_PROTOCOL_CAPABILITY*/ulong capabilities;/// 
UID if provided by hardware (see uid2)   [Units("")][Description("UID if provided by hardware (see uid2)")]public  ulong uid;/// 
Firmware version number   [Units("")][Description("Firmware version number")]public  uint flight_sw_version;/// 
Middleware version number   [Units("")][Description("Middleware version number")]public  uint middleware_sw_version;/// 
Operating system version number   [Units("")][Description("Operating system version number")]public  uint os_sw_version;/// 
HW / board version (last 8 bytes should be silicon ID, if any)   [Units("")][Description("HW / board version (last 8 bytes should be silicon ID, if any)")]public  uint board_version;/// 
ID of the board vendor   [Units("")][Description("ID of the board vendor")]public  ushort vendor_id;/// 
ID of the product   [Units("")][Description("ID of the product")]public  ushort product_id;/// 
Custom version field, commonly the first 8 bytes of the git hash. This is not an unique identifier, but should allow to identify the commit using the main version number even for very large code bases.   [Units("")][Description("Custom version field, commonly the first 8 bytes of the git hash. This is not an unique identifier, but should allow to identify the commit using the main version number even for very large code bases.")][MarshalAs(UnmanagedType.ByValArray,SizeConst=8)]public byte[] flight_custom_version;/// 
Custom version field, commonly the first 8 bytes of the git hash. This is not an unique identifier, but should allow to identify the commit using the main version number even for very large code bases.   [Units("")][Description("Custom version field, commonly the first 8 bytes of the git hash. This is not an unique identifier, but should allow to identify the commit using the main version number even for very large code bases.")][MarshalAs(UnmanagedType.ByValArray,SizeConst=8)]public byte[] middleware_custom_version;/// 
Custom version field, commonly the first 8 bytes of the git hash. This is not an unique identifier, but should allow to identify the commit using the main version number even for very large code bases.   [Units("")][Description("Custom version field, commonly the first 8 bytes of the git hash. This is not an unique identifier, but should allow to identify the commit using the main version number even for very large code bases.")][MarshalAs(UnmanagedType.ByValArray,SizeConst=8)]public byte[] os_custom_version;/// 
UID if provided by hardware (supersedes the uid field. If this is non-zero, use this field, otherwise use uid)   [Units("")][Description("UID if provided by hardware (supersedes the uid field. If this is non-zero, use this field, otherwise use uid)")][MarshalAs(UnmanagedType.ByValArray,SizeConst=18)]public byte[] uid2;};}

█ 相关资料

提示：这里是参考的相关文章

1. mavlink官网：MAVLink
2. pixhawk官网：Mavlink 消息简介 - pixhawk
3. 2020-10-06 ardupilot 如何为android 增加mavlink协议_陌城烟雨-CSDN博客
4. 打造自己的HelloDrone 无人机APP过程《2》_陌城烟雨-CSDN博客_drone无人机怎么下app
5. 2015-04-02 Mavlink协议理解Pixhawk APM（一）_super_mice的专栏-CSDN博客
6. 2018-12-24 无人机中级篇：第十四讲：外部通信总线Mavlink服务 - 知乎
7. 2019-02-15 MAVLINK 请求参数和接收参数_小马哔哔-CSDN博客
8. 很直白：2020-02-06 MAVLink笔记 #02# MAVLink绝对傻瓜教程（译） - xkfx - 博客园

█ 免责声明

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