java - Raspberry Pi 从 MultiWii 获取数据

Question

我有一个 Raspberry Pi 3B 和一个 CRIUS All in One Pro (v2.0) MultiWii 飞行 Controller 。我正在使用 MultiWii 2.4 版本和最新的 NOOBS。我能够很好地设置两者，现在我尝试让 Raspberry Pi 通过连接两 block 板的 USB/Micro USB 电缆与 MultiWii 进行通信。

目前，MultiWii 没有返回任何数据，我不知道为什么。据我所知，我的协议(protocol)是正确的。我查看了几个工作代码存储库(用 Python 或 Java 为 Arduino 编写)，并遵循了 MultiWii documentation并通读相关的 forum post .

这是我编写的客户端代码。

package com.jmace.MaceDrone.msp;


import com.pi4j.io.serial.Baud;
import com.pi4j.io.serial.DataBits;
import com.pi4j.io.serial.FlowControl;
import com.pi4j.io.serial.Parity;
import com.pi4j.io.serial.Serial;
import com.pi4j.io.serial.SerialConfig;
import com.pi4j.io.serial.SerialDataEvent;
import com.pi4j.io.serial.SerialDataEventListener;
import com.pi4j.io.serial.SerialFactory;
import com.pi4j.io.serial.StopBits;
import java.io.IOException;
import java.math.BigInteger;

public class MultiWiiClient {

    private final Serial serial;

    //The preamble is defined by the protocol.
    //Every message must begin with the characters $M
    private static final String PREAMBLE = "$M";
    //Character that denotes information being passed to the MultiWii
    private static final char TO_MUTLIWII = '<';
    //Character that denotes information being requested from by the MultiWii
    private static final char FROM_MUTLIWII = '>';

    public MultiWiiClient(String usbPort) {
        SerialConfig config = new SerialConfig();
        config.device(usbPort)
              .baud(Baud._115200)
              .dataBits(DataBits._8)
              .parity(Parity.NONE)
              .stopBits(StopBits._1)
              .flowControl(FlowControl.NONE);

        this.serial = SerialFactory.createInstance();

        serial.addListener(new SerialDataEventListener() {
            @Override
            public void dataReceived(SerialDataEvent event) {
                try {
                    System.out.println("[HEX DATA]   " + event.getHexByteString());
                    System.out.println("[ASCII DATA] " + event.getAsciiString());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        });

        try {
            this.serial.open(config);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }


    public String sendRequest(MultiWiiRequest request) throws IllegalStateException, IOException {
        String message = createMessage(request.getId(), false, null);
        //////////////////////////////////////////////////////////////////////////////////
        System.out.println(message);
        System.out.println(String.format("%040x", new BigInteger(1, message.getBytes())));
        //////////////////////////////////////////////////////////////////////////////////
        return sendMessage(message);
    }


    public String sendCommand(MultiWiiCommand command, String payload) throws IllegalStateException, IOException {
        String message = createMessage(command.getId(), true, payload);
        return sendMessage(message);
    }

    /**
     * This method creates the message that will be sent to the MultiWii
     * 
     * Message format is as follows:
     * +--------+---------+----+-------+----+---+
     * |preamble|direction|size|command|data|crc|
     * +--------+---------+----+-------+----+---+
     * 
     * Preamble (2 bytes):
     *      Marks the start of a new message; always "$M"
     * 
     * Direction (1 byte):
     *      Either '<' for a command going to the MultiWii or '>' for
     *      information being requested from the MultiWii
     * 
     * Size (1 byte):
     *      The number of bytes in the payload
     * 
     * Command (1 byte):
     *      The message ID of the command, as defined in the protocol
     *      100's for requesting data, and 200's for requesting an action
     * 
     * Data (variable bytes):
     *      The data to pass along with the command
     * 
     * CRC (1 byte):
     *      Calculated with an XOR of the size, command, and each byte of data 
     */
    private String createMessage(int mutliWiiCommandnumber, boolean isCommand, String payload) {
        StringBuilder message = new StringBuilder(PREAMBLE);
        byte checksum=0;

        //Get the direction of the message
        if (isCommand) {
            message.append(TO_MUTLIWII);
        } else {
            message.append(FROM_MUTLIWII);
        }

        int datalength = (payload != null) ? payload.length() : 0;

        message.append((char) datalength);
        checksum ^= datalength;

        message.append((char) mutliWiiCommandnumber);
        checksum ^= ((int) mutliWiiCommandnumber);

        if (payload != null) {
            for (char c : payload.toCharArray()){ 
                message.append(c);
                checksum ^= (int) c;
            }
        }

        message.append((char) checksum);
        return message.toString();
    }


    private String sendMessage(String message) throws IllegalStateException, IOException {
        serial.write(message.getBytes());

        serial.flush();
        System.out.println("TESTING ------------------");

        return "";
    }

}

我正在使用“/dev/ttyUSB0”进行连接，我确认这是正确的位置并且它似乎正在工作(运行时没有错误；如果我开始运行然后断开 USB，它会抛出异常，因为它失去了连接)。

运行时，我得到以下输出(发送命令 100，MSP_IDENT):

$M>dd
00000000000000000000000000244d3e006464
TESTING ------------------

参见my Git repo了解更多代码上下文。

编辑:修复了我帖子中的校验和代码

Answer 1

我发现问题出在我的方向上。我认为“<”用于发送命令，“>”用于请求数据。事实证明，在这两种情况下，都应该使用“<”。仅当 MultiWii 响应时才使用“>”字符。