MAVLink协议：
MavLink协议目前网上可以找到的中文版资料只有1.0的。现在开发使用的固件版本号是1.7.3.串口抓的的包全部与1.0版本都不一致。爬到官方去看了下。有2.0的包结构。
uint8_t magic; ///< protocol magic marker
uint8_t len; ///< Length of payload
uint8_t incompat_flags; ///< flags that must be understood
uint8_t compat_flags; ///< flags that can be ignored if not understood
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 target_sysid; ///< Optional field for point-to-point messages, used for payload else
uint8_t target_compid; ///< Optional field for point-to-point messages, used for payload else
uint8_t payload[max 253]; ///< A maximum of 253 payload bytes
uint16_t checksum; ///< X.25 CRC
uint8_t signature[13]; ///< Signature which allows ensuring that the link is tamper-proof
包结构大致如下：
| 部分 | 长度 | 内容 |
|---|---|---|
| n1 STX | 1B | 帧头部分，2.0版本为 0xFD |
| n2 LEN | 1B | PLAYLOAD数据长度 |
| n3 | 1B | incompat_flags |
| n4 | 1B | compat_flags |
| n5 SEQ | 1B | 消息帧序号 |
| n6 SYS | 1B | 消息系统编号 |
| n7 COMP | 1B | 罗盘编号 |
| n8 MSG | 3B | msgid,消息标号，MavlinkMessage |
| n9 | 1B | target_sysid可选 |
| n10 | 1B | target_compid可选 |
| n11 PLAYLOAD | 2B | 消息内容 |
| n12 | 2B | CRC校验 |
| n13 | 1B | 签名 |
2.0包的总长为10+n+3(+2),其中括号的2为可选内容。抓包未发现。
抓包获得来自飞控的Msgind如下。
0,36,74,105,30,31,32,140,1,147,65,70,141,230,241,111,83,69,24
這些都是飞控无请求时主动发送过来的数据。
根据msgid：
| HEX | DEC | TYPE |
|---|---|---|
| 00 | 0 | HEARTBEAT |
| 01 | 1 | SYS_STATUS |
| 18 | 24 | GPS_RAW_INT |
| 1E | 30 | ATTITUDE |
| 1F | 31 | ATTITUDE_QUATERNION |
| 20 | 32 | LOCAL_POSITION_NED |
| 24 | 36 | SERVO_OUTPUT_RAW |
| 41 | 65 | RC_CHANNELS |
| 45 | 69 | MANUAL_CONTROL |
| 46 | 70 | RC_CHANNELS_OVERRIDE |
| 4A | 74 | VFR_HUD |
| 53 | 83 | ATTITUDE_TARGET |
| 69 | 105 | HIGHRES_IMU |
| 6F | 111 | TIMESYNC |
| 8C | 140 | ACTUATOR_CONTROL_TARGET |
| 8D | 141 | ALTITUDE |
| 93 | 147 | BATTERY_STATUS |
| E6 | 230 | ESTIMATOR_STATUS |
| E7 | 231 | WIND_COV |
| F1 | 241 | VIBRATION |
| F5 | 245 | EXTENDED_SYS_STATE |
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