如何使用 usb-serial-for-android 从连接到 Android 的 CDC 设备读取数据？

Question

我正在使用这个 library 从 Feather 32u4 设备发送和接收数据。 Feather 在端口打开时发送一些固定数据，然后回显发送给它的内容。

我在理解 read 和 write 方法在库中的工作方式时遇到问题。我很确定我使用 write 是正确的，但我不知道 read。使用 read 时返回的长度始终为 0，我使用的是正确的波特率。我只是不太确定如何使用它。我还在尝试找出事件驱动选项。

private void DoTheThing () {

      String textMessage = "";

      UsbManager manager = (UsbManager) getSystemService(Context.USB_SERVICE);



      // Find available drivers for Feather board.
      ProbeTable customTable = new ProbeTable();
      customTable.addProduct(0x239a, 0x800c, CdcAcmSerialDriver.class);
      UsbSerialProber prober = new UsbSerialProber(customTable);
      List<UsbSerialDriver> drivers = prober.findAllDrivers(manager);
      if (drivers.isEmpty()) {
         textMessage += "Could not find any drivers.\n";
         m_textView.setText(textMessage);
         return;
      }

      textMessage += "Driver found\n";
      m_textView.setText(textMessage);

      UsbDeviceConnection connection = null;
      UsbSerialDriver driver = drivers.get(0);
      PendingIntent usbPermissionIntent = PendingIntent.getBroadcast(this, 0, new Intent(INTENT_ACTION_GRANT_USB), 0);
      manager.requestPermission(driver.getDevice(), usbPermissionIntent);
      try {
         connection = manager.openDevice(driver.getDevice());
      } catch (Exception e) {
         textMessage += e + "\n";
         m_textView.setText(textMessage);
      }
      if (connection == null) {
         // add UsbManager.requestPermission(driver.getDevice(), ..) handling here
         textMessage += "Could not open device.\n";
         m_textView.setText(textMessage);
         return;
      }

      textMessage += "Device opened\n";
      m_textView.setText(textMessage);

      UsbSerialPort port = driver.getPorts().get(0);
      // Most devices have just one port (port 0)
      try {
         port.open(connection);
         port.setParameters(115200, 8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE);
      } catch (IOException e) {
         textMessage += e + "\n";
         m_textView.setText(textMessage);
         return;
      }

      textMessage += "Connection established\n";
      m_textView.setText(textMessage);

      // Get received data on connection.
      int length = -2;
      byte[] receivedData = new byte[64];
      try {
         length = port.read(receivedData, 2000);
      } catch (Exception e) {
         textMessage += "Oops: " + e + "\n";
         m_textView.setText(textMessage);
      }

      String data = new String(receivedData);
      textMessage += "Data recieved: " + length + " " + data + "\n";
      m_textView.setText(textMessage);


      // Send canned data.
      length = -2;
      try {
         length = port.write("a".getBytes(), 2000);
      } catch (Exception e) {
         textMessage += "Oops: " + e + "\n";
         m_textView.setText(textMessage);
      }

      textMessage += "Data sent " + length + "\n";
      m_textView.setText(textMessage);

      // Get received data.
      length = -2;
      receivedData = new byte[64];
      try {
         length = port.read(receivedData, 2000);
      } catch (Exception e) {
         textMessage += "Oops: " + e + "\n";
         m_textView.setText(textMessage);
      }

      data = new String(receivedData);
      textMessage += "Data recieved: " + length + " " + data;
      m_textView.setText(textMessage);

   }

编辑

当我在我的端口上将 DTR 标志设置为 true 时发生严重崩溃。

m_port = driver.getPorts().get(0); // Most devices have just one port (port 0) try { m_port.setDTR(true); // <-- hard crash m_port.open(connection); m_port.setParameters(115200, 8, UsbSerialPort.STOPBITS_1, UsbSerialPort.PARITY_NONE); } catch (IOException e) { m_textMessage += e + "\n"; m_textView.setText(m_textMessage); return; }

~~难道m_port到那个时候还没有初始化吗？~~

德普

Answer 1

当在 2000 毫秒超时内未收到任何内容时，长度为 0。

对于像 32u4 这样的 CDC 设备，您通常必须按照所述设置 DTR 线 here

如何使用 usb-serial-for-android 从连接到 Android 的 CDC 设备读取数据？

How to read for data from CDC device connected to Android using usb-serial-for-android?

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usbserial

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