# MAVSDK Android serial problem

**URL:** <https://discuss.px4.io/t/mavsdk-android-serial-problem/43264>\
**Category:** MAVSDK\
**Created:** [January 13, 2025, 9:33am UTC](https://discuss.px4.io/t/mavsdk-android-serial-problem/43264 "2025-01-13T09:33:02Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![Johnny\_Deng](https://discuss.px4.io/user_avatar/discuss.px4.io/johnny_deng/32/18207_2.png) [@Johnny\_Deng](https://discuss.px4.io/u/Johnny_Deng)\
**Post date:** [January 13, 2025, 9:33am UTC](https://discuss.px4.io/t/mavsdk-android-serial-problem/43264/1 "2025-01-13T09:33:02Z")

</div>

We need to use Type-C to connect an Android app on a phone to a drone for communication.

We use MAVSDK Android to connect via Type-C, but we encountered an issue where serial access fails due to a lack of Linux file permissions. We are not root users and cannot gain root access. However, we noticed that the Android version of QGC also operates as a regular user but is able to establish a connection.

Through investigation, I found there are two possible approaches:

1. 1、Using one java thread reading from serial using Android SDK api, forwarding to mavsdk server on like UDP:14550, and the other tread receiving data from mavsdk server UDP:14550, sending to serial (through Android SDK)

2. 2、Using **[divyanshupundir](https://github.com/divyanshupundir)**  **'s andriod-serial git branch, compile by myself… Using the new fileDiscripitor interface to read and write by madsdk server directly…**

**I tried both… Seems not working neither… Am I wrong somewhere?**

**Below are codes of approach 1:**

private void startForwardThreads() {

```
stopForwardThreads(); // 确保在启动新线程前停止旧线程

running.set(true);
// 启动 UDP→serial 的线程
executor.execute(() -> {
    byte[] buffer = new byte[READ_BUFFER_SIZE];
    DatagramPacket packet = new DatagramPacket(buffer, buffer.length);
    Log.i(TAG, "UDP→串口 线程启动");

    while (running.get()) {
        try {
            if (udpSocket == null || udpSocket.isClosed()) {
                Log.w(TAG, "UDP Socket 未初始化或已关闭，等待重新初始化...");
                try {
                    Thread.sleep(1000); // 避免高频错误
                } catch (InterruptedException ie) {
                    Thread.currentThread().interrupt();
                    break;
                }
                continue;
            }

            udpSocket.receive(packet);
            int len = packet.getLength();
            if (len > 0) {
                Log.i(TAG, "从 UDP 接收到消息: " + bytesToHex(packet.getData(), len));
                writeToSerial(packet.getData(), len);
            }
            packet.setLength(buffer.length);

        } catch (IOException e) {
            if (running.get()) {
                Log.w(TAG, "UDP 接收错误: " + e.getMessage());
            }
            try {
                Thread.sleep(1000); // 避免高频错误
            } catch (InterruptedException ie) {
                Thread.currentThread().interrupt();
                break;
            }
        }
    }

    Log.i(TAG, "UDP→串口 线程已停止");
});

// 启动 serial→UDP 的线程
executor.execute(() -> {
    byte[] buffer = new byte[READ_BUFFER_SIZE];
    int readFailCount = 0;
    Log.i(TAG, "串口→UDP 线程启动");

    while (running.get()) {
        try {
            int len = serialPort.read(buffer, READ_WAIT_MILLIS);
            if (len > 0) {
                readFailCount = 0;
                forwardToUDP(buffer, len);
            }
        } catch (IOException e) {
            readFailCount++;
            Log.w(TAG, "串口读取失败，当前重试次数：" + readFailCount);
            if (readFailCount >= MAX_READ_FAILS) {
                handleConnectionLoss();
                break;
            }
            try {
                Thread.sleep(2000);
            } catch (InterruptedException ie) {
                Thread.currentThread().interrupt();
                break;
            }
        }
    }

    Log.i(TAG, "串口→UDP 线程已停止");
});

```

}

**Approach 2 LOG:**

 ![image](https://discuss.px4.io/uploads/default/original/3X/f/5/f527a0bb2fb0dfe5d70311a9d6ce1e0602341edc.png)  
 ![image](https://discuss.px4.io/uploads/default/original/3X/b/c/bcc6082764b9b428e5eb59d175d343e80a25acf4.png)