MWC飞控V2.3串口通信协议
在V2.3版的change.txt中有这么一段话：
main changes 2.2 -> 2.3
...
RCSERIAL is now deeply integrated. If a MSP_SET_RAW_RC comes, it will just override legacy RX data. (r1420)
as a consequence, RCSERIAL is no more an option在这之前，想用串口控制飞控的方法是去选择RCSERIAL这个预编译选项等等，现在 RCSERIAL 已经被深度集成，如果我们给飞控发送一个MSP_SET_RAW_RC 指令同时带上控制数据，那就可以控制飞控了。于是RCSERIAL 不复存在，这就要求我们要去了解串口协议。
关于串口协议的一段话：
updated 04 July
Multiwii serial protocol was redesigned://优点等等• to be light, as before• to be generic: it can be used transparenlty by a GUI, OSD, telemetry or home made config tool.ie no more specific OSD code should be coded in multiwii• to be bit wire efficient: only requested data are transmitted in a binary format• to be quite secure: data are sent with a checksum, preventing corrupted configuration to be injected.• to be header sensitive: as it is designed with a specific header, it can be mixed with other frame, like GPS frameie, it will be possible to connect either a GUI or a GPS on the same serial port without changing the conf• to be less sensitive to evolutions:ie in case of parameter evolution, the main protocol will remain compatible and the GUI will be much less version dependent.variable data length allows to consider only the beginning of a message, leaving the other octets at the end to extend transparently the message (for instance to add a new PID)I thought first about an implementation of Mavlink, but I think it's not what I was looking for.Even with a partial implementation, the predefined structures are not light enough for what I have in mind.Some messages are however inspired from mavlink structure.The main rule remains: Multiwii never sends something on its own.A request must be done in each case to retrieve or set data.Each messages received are acknowledged even if there is no data inside.There are 2 main messages to consider:•request message to multiwii•multiwii output message //一句话：一问一答，不问不答
/*重点来了:指令格式*/
request message to multiwii //從飞控中讀取信息To request simple data without parameters / send a specific command / inject new parameters in multiwiimessages are formated like this:$M>[data length][code][data][checksum]1 octet '$'1 octet 'M'1 octet '<'1 octet [data length]1 octet [code]several octets [data]1 octet [checksum][data length] can be 0 in case of no param command //也就是说如果只发一个指令不带数据的话数据长度可以为0multiwii output message //向飞控输出信息messages are formated like this:$M>[data length][code][data][checksum]1 octet '$'1 octet 'M'1 octet '>'1 octet [data length]1 octet [code]several octets [data]1 octet [checksum]if the message is unknown://未知信息
$M|[0][code][checksum]1 octet '$'1 octet 'M'1 octet '|'1 octet 01 octet [unknown code]1 octet [checksum]
总结下：
- 读写信息格式：前綴 ’$M‘ 加 '<'或'>' (分別代表讀寫) 加 数据长度 加 指令代码 加 实际数据 加 校验码
以上均已字节为单位，且不含空格
- 前綴换算成16进制的指令格式长这样：
读：24 4D 3C //$M<
写：24 4D 3E //$M>
- 关于校验码
参照官方的MultiWiiConf程序，我写了一个用于计算校验码的C++函数（要求数据长度大于0，如果等于0校验码与指令代码相同）
byte getChecksum(byte length,byte cmd,byte mydata[]) //三个参数分别为： 数据长度 ， 指令代码 ， 实际数据数组
typedef unsigned char byte;byte getChecksum(byte length,byte cmd,byte mydata[]){ byte checksum=0; checksum ^= (length&0xFF); checksum ^= (cmd&0xFF); for(int i=0;i - 注意波特率要选115200
- 示例：串口以16进制发送：24 4D 3C 00 64 64 ，飞控将返回版本信息等等数据。
00表示数据长度为0；
第一个64为指令代码，即下面网址上的第一个代码
第一个64为校验码
其它：
- 飞控上的程序在Protocol.cpp中进行串口通信处理，具体函数为serialCom()
- 官方上的协议资料可以了解到指令代码（message_id），和指令方向以及指令内容等内容