android串口讨论问题

为什么我的tiny4412开发板只能发送数据而不能接收数据。
代码如下：
private class ReadThread extends Thread{

            @Override
            public void run() {
                super.run();
                while (!isInterrupted()) {
                    int size;
                    try {

                        if (inputStream == null)
                            return;
                        byte[] buffer = new byte[1024];

                        size = inputStream.read(buffer);
                        //   Log.i("test","接收数据长度"+size);
                        if (size > 0) {
                            onDataReceived(buffer, size);
                        }
                    }
                    catch (IOException e) {
                        e.printStackTrace();
                        return;
                    }
                    //mReception.append(new String("receive"));
                }
                // Log.e("test","跳出循环");
            }
        }

    void onDataReceived(final byte[] buffer, final int size) {
        runOnUiThread(new Runnable() {
            public void run() {
                Log.i("test","显示数据");

                mReception.append(new String(buffer, 0, size));

            }
        });
    }
接收数据的时候没有任何显示