java - Raspberry Pi从MultiWii获取数据

我有一个Raspberry Pi 3B和一个CRIUS All in One Pro（v2.0）MultiWii飞行控制器。我正在使用MultiWii 2.4版本和最新的NOOBS。我能够很好地进行设置，现在我正在尝试使Raspberry Pi通过连接两块板的USB / Micro USB电缆与MultiWii通信。

目前，MultiWii不会返回任何数据，我不确定为什么。从我所看到的，我有正确的协议。我看过几个工作代码存储库（使用Java for Arduino的Python编写），并遵循MultiWii documentation并通读了相关的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，并且似乎可以正常运行（运行时没有错误；并且如果我开始运行然后断开USB的连接，则会抛出异常，因为它断开连接）。

运行时，我得到以下输出（发送命令100，MSP_IDENT）：

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

有关更多代码上下文，请参见my Git repo。

编辑：修复了我帖子中的校验和代码

最佳答案

我发现问题出在我的方向上。我虽然有''用于请求数据。事实证明，在两种情况下都应使用“ '字符。