Android串口Serial服务解析
16lz
2021-01-23
正常Android设备的串口一般是用作debug调试使用，随着Android设备使用越来越广，比如智能pos、智能扫码机都会用到Android主板和单片机进行通信，如果Android主板和单片机通信数据量大可以使用USB，若是通信数据量小可以使用串口进行通信，因为串口通信简单并且稳定性高，最近做的一个项目就是Android使用串口和加密芯片进行通信，Android主板使用的是rk3288和rk3368. 在rk3288源码中集成了一个串口demo，目录在
rk3288/frameworks/base/tests/SerialChat网上存在一个demo是通过 java->jni->Serial驱动，虽然也可以正常读写，这样做缺点是
1、如果突然串口不能正常通信可能会导致app崩溃，
2、这个串口只能被当前的app使用，其他app 不能使用。
3、违背正常Android设计初衷，Android标准流程是
java->service->jni->hal->serial驱动。
所以我在项目中使用了Android源码中的demo
public class SerialChat extends Activity implements Runnable, TextView.OnEditorActionListener { private static final String TAG = "SerialChat"; private TextView mLog; private EditText mEditText; private ByteBuffer mInputBuffer; private ByteBuffer mOutputBuffer; private SerialManager mSerialManager; private SerialPort mSerialPort; private boolean mPermissionRequestPending; private static final int MESSAGE_LOG = 1; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); mSerialManager = (SerialManager)getSystemService(Context.SERIAL_SERVICE); setContentView(R.layout.serial_chat); mLog = (TextView)findViewById(R.id.log); mEditText = (EditText)findViewById(R.id.message); mEditText.setOnEditorActionListener(this); if (false) { mInputBuffer = ByteBuffer.allocateDirect(1024); mOutputBuffer = ByteBuffer.allocateDirect(1024); } else { mInputBuffer = ByteBuffer.allocate(1024); mOutputBuffer = ByteBuffer.allocate(1024); } } @Override public void onResume() { super.onResume(); String[] ports = mSerialManager.getSerialPorts();for(int 1 = 0;i < ports.length;i++ ){Log.e("PPTV", "ports is ====" + ports[i] );} if (ports != null && ports.length > 0) { try { mSerialPort = mSerialManager.openSerialPort(ports[1], 115200); if (mSerialPort != null) { new Thread(this).start(); } } catch (IOException e) { } } } @Override public void onPause() { super.onPause(); } @Override public void onDestroy() { if (mSerialPort != null) { try { mSerialPort.close(); } catch (IOException e) { } mSerialPort = null; } super.onDestroy(); } public boolean onEditorAction(TextView v, int actionId, KeyEvent event) { if (/* actionId == EditorInfo.IME_ACTION_DONE && */ mSerialPort != null) { try { String text = v.getText().toString(); Log.d(TAG, "write: " + text); byte[] bytes = text.getBytes(); mOutputBuffer.clear(); mOutputBuffer.put(bytes); mSerialPort.write(mOutputBuffer, bytes.length); } catch (IOException e) { Log.e(TAG, "write failed", e); } v.setText(""); return true; } Log.d(TAG, "onEditorAction " + actionId + " event: " + event); return false; } public void run() { Log.d(TAG, "run"); int ret = 0; byte[] buffer = new byte[1024]; while (ret >= 0) { try { Log.d(TAG, "calling read"); mInputBuffer.clear(); ret = mSerialPort.read(mInputBuffer); Log.d(TAG, "read returned " + ret); mInputBuffer.get(buffer, 0, ret); } catch (IOException e) { Log.e(TAG, "read failed", e); break; } if (ret > 0) { Message m = Message.obtain(mHandler, MESSAGE_LOG); String text = new String(buffer, 0, ret); Log.d(TAG, "chat: " + text); m.obj = text; mHandler.sendMessage(m); } } Log.d(TAG, "thread out"); } Handler mHandler = new Handler() { @Override public void handleMessage(Message msg) { switch (msg.what) { case MESSAGE_LOG: mLog.setText(mLog.getText() + (String)msg.obj); break; } } };}首先是获取串口服务
mSerialManager = (SerialManager)getSystemService(Context.SERIAL_SERVICE);如果要想通过getSystemService获取serial服务，首先要在
core/java/android/content/Context.java:
添加
public static final String SERIAL_SERVICE = "serial";在ContextImpl.java 中注册服务
registerService(SERIAL_SERVICE, new ServiceFetcher() { public Object createService(ContextImpl ctx) { IBinder b = ServiceManager.getService(SERIAL_SERVICE); return new SerialManager(ctx, ISerialManager.Stub.asInterface(b)); }});每次开机会自动启动。可以通过命令查看当前服务是否启动
adb shell service list
可以看到服务已经启动。
目前启动的服务Java层面的服务，只是对我们C语言串口服务做了一层封装，真正工作的是我们native serial(SerialService).
所以registerService 函数中会获取SerialService的代理端，
IBinder b = ServiceManager.getService(SERIAL_SERVICE); return new SerialManager(ctx, ISerialManager.Stub.asInterface(b));SerialService 注册在SystemServer.java 中
try { Slog.i(TAG, "Serial Service"); // Serial port support serial = new SerialService(context); ServiceManager.addService(Context.SERIAL_SERVICE, serial); } catch (Throwable e) { Slog.e(TAG, "Failure starting SerialService", e); } }SerialService.java 源码
public class SerialService extends ISerialManager.Stub { private final Context mContext; private final String[] mSerialPorts; public SerialService(Context context) { mContext = context; mSerialPorts = context.getResources().getStringArray( com.android.internal.R.array.config_serialPorts); } public String[] getSerialPorts() { mContext.enforceCallingOrSelfPermission(android.Manifest.permission.SERIAL_PORT, null); ArrayList ports = new ArrayList(); for (int i = 0; i < mSerialPorts.length; i++) { String path = mSerialPorts[i]; if (new File(path).exists()) { ports.add(path); } } String[] result = new String[ports.size()]; ports.toArray(result); return result; } public ParcelFileDescriptor openSerialPort(String path) { mContext.enforceCallingOrSelfPermission(android.Manifest.permission.SERIAL_PORT, null); for (int i = 0; i < mSerialPorts.length; i++) { if (mSerialPorts[i].equals(path)) { return native_open(path); } } throw new IllegalArgumentException("Invalid serial port " + path); } private native ParcelFileDescriptor native_open(String path);} mContext = context; mSerialPorts = context.getResources().getStringArray( com.android.internal.R.array.config_serialPorts);会获取目前存在可以使用串口列表。这个根据自己需要添加。
我的就使用一个串口3
- "/dev/ttyS3"
回到SerialChat.java
String[] ports = mSerialManager.getSerialPorts(); 结果就是/dev/ttyS3
mSerialPort = mSerialManager.openSerialPort(ports[1], 115200);打开串口3
public SerialPort openSerialPort(String name, int speed) throws IOException { try { ParcelFileDescriptor pfd = mService.openSerialPort(name);//打开串口 if (pfd != null) { SerialPort port = new SerialPort(name); port.open(pfd, speed);//设置波特率及其他属性 return port; } else { throw new IOException("Could not open serial port " + name); } } catch (RemoteException e) { Log.e(TAG, "exception in UsbManager.openDevice", e); } return null; }结果会调用SerialService.openSerialPort(name)
public ParcelFileDescriptor openSerialPort(String path) { mContext.enforceCallingOrSelfPermission(android.Manifest.permission.SERIAL_PORT, null); for (int i = 0; i < mSerialPorts.length; i++) { if (mSerialPorts[i].equals(path)) { return native_open(path); } } throw new IllegalArgumentException("Invalid serial port " + path); }最终打开调用native_open 通过jni方式打开串口3。
static jobject android_server_SerialService_open(JNIEnv *env, jobject thiz, jstring path){ const char *pathStr = env->GetStringUTFChars(path, NULL); int fd = open(pathStr, O_RDWR | O_NOCTTY); if (fd < 0) { ALOGE("could not open %s", pathStr); env->ReleaseStringUTFChars(path, pathStr); return NULL; } env->ReleaseStringUTFChars(path, pathStr); jobject fileDescriptor = jniCreateFileDescriptor(env, fd); if (fileDescriptor == NULL) { return NULL; } return env->NewObject(gParcelFileDescriptorOffsets.mClass, gParcelFileDescriptorOffsets.mConstructor, fileDescriptor);}阻塞的方式打开串口
设置串口波特率已经属性
android_hardware_SerialPort.cpp
static voidandroid_hardware_SerialPort_open(JNIEnv *env, jobject thiz, jobject fileDescriptor, jint speed){ switch (speed) { case 50: speed = B50; break; case 75: speed = B75; break; case 110: speed = B110; break; case 134: speed = B134; break; case 150: speed = B150; break; case 200: speed = B200; break; case 300: speed = B300; break; case 600: speed = B600; break; case 1200: speed = B1200; break; case 1800: speed = B1800; break; case 2400: speed = B2400; break; case 4800: speed = B4800; break; case 9600: speed = B9600; break; case 19200: speed = B19200; break; case 38400: speed = B38400; break; case 57600: speed = B57600; break; case 115200: speed = B115200; break; case 230400: speed = B230400; break; case 460800: speed = B460800; break; case 500000: speed = B500000; break; case 576000: speed = B576000; break; case 921600: speed = B921600; break; case 1000000: speed = B1000000; break; case 1152000: speed = B1152000; break; case 1500000: speed = B1500000; break; case 2000000: speed = B2000000; break; case 2500000: speed = B2500000; break; case 3000000: speed = B3000000; break; case 3500000: speed = B3500000; break; case 4000000: speed = B4000000; break; default: jniThrowException(env, "java/lang/IllegalArgumentException", "Unsupported serial port speed"); return; } int fd = jniGetFDFromFileDescriptor(env, fileDescriptor); // duplicate the file descriptor, since ParcelFileDescriptor will eventually close its copy fd = dup(fd); if (fd < 0) { jniThrowException(env, "java/io/IOException", "Could not open serial port"); return; } env->SetIntField(thiz, field_context, fd); struct termios tio; if (tcgetattr(fd, &tio)) memset(&tio, 0, sizeof(tio)); tio.c_cflag = speed | CS8 | CLOCAL | CREAD; // Disable output processing, including messing with end-of-line characters. tio.c_oflag &= ~OPOST; tio.c_iflag = IGNPAR;// 忽略奇偶校验错误 tio.c_lflag = 0; /* turn of CANON, ECHO*, etc */ /* no timeout but request at least one character per read */ tio.c_cc[VTIME] = 0;//如果读取不到就一直等待 tio.c_cc[VMIN] = 1;//读取一个byte就返回 tcsetattr(fd, TCSANOW, &tio); tcflush(fd, TCIOFLUSH);}到这里open 串口完成
串口写很简单。就不解析了。重点解析read ，由于我们是block 方式打开的串口，所以如果没有数据流返回，串口会一直阻塞
public void run() { Log.d(TAG, "run"); int ret = 0; byte[] buffer = new byte[1024]; while (ret >= 0) { try { Log.d(TAG, "calling read"); mInputBuffer.clear(); ret = mSerialPort.read(mInputBuffer); Log.d(TAG, "read returned " + ret); mInputBuffer.get(buffer, 0, ret); } catch (IOException e) { Log.e(TAG, "read failed", e); break; } if (ret > 0) { Message m = Message.obtain(mHandler, MESSAGE_LOG); String text = new String(buffer, 0, ret); Log.d(TAG, "chat: " + text); m.obj = text; mHandler.sendMessage(m); } } Log.d(TAG, "thread out"); } Handler mHandler = new Handler() { @Override public void handleMessage(Message msg) { switch (msg.what) { case MESSAGE_LOG: mLog.setText(mLog.getText() + (String)msg.obj); break; } } };}开启一个thread方式read 串口数据，
无数据会一直阻塞在ret = mSerialPort.read(mInputBuffer);
另外注意 的是读写buffer 要是用
private ByteBuffer mInputBuffer; private ByteBuffer mOutputBuffer;收到数据可以保存到普通的 byte[]中。
public int read(ByteBuffer buffer) throws IOException { if (buffer.isDirect()) { return native_read_direct(buffer, buffer.remaining()); } else if (buffer.hasArray()) { return native_read_array(buffer.array(), buffer.remaining()); } else { throw new IllegalArgumentException("buffer is not direct and has no array"); } }调用底层的c语言的read函数
static jintandroid_hardware_SerialPort_read_direct(JNIEnv *env, jobject thiz, jobject buffer, jint length){ int fd = env->GetIntField(thiz, field_context); jbyte* buf = (jbyte *)env->GetDirectBufferAddress(buffer); if (!buf) { jniThrowException(env, "java/lang/IllegalArgumentException", "ByteBuffer not direct"); return -1; } int ret = read(fd, buf, length); if (ret < 0) jniThrowException(env, "java/io/IOException", NULL); return ret;}更多相关文章
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