Android基于串口通讯笔记（USB，485协议,232协议）

串口通信（Serial Communications）的概念非常简单，串口按位（bit）发送和接收字节。尽管比按字节（byte）的并行通信慢，但是串口可以在使用一根线发送数据的同时用另一根线接收数据。它很简单并且能够实现远距离通信。比如IEEE488定义并行通行状态时，规定设备线总长不得超过20米，并且任意两个设备间的长度不得超过2米；而对于串口而言，长度可达1200米。典型地，串口用于ASCII码字符的传输。通信使用3根线完成，分别是地线、发送、接收。由于串口通信是异步的，端口能够在一根线上发送数据同时在另一根线上接收数据。其他线用于握手，但不是必须的。串口通信最重要的参数是波特率、数据位、停止位和奇偶校验。对于两个进行通信的端口，这些参数必须匹配。

传输方式不同、传输距离不同、RS-232 只允许一对一通信。

1、传输方式不同。 RS-232采取不平衡传输方式，即所谓单端通讯. 而RS485则采用平衡传输，即差分传输方式。

2、传输距离不同。RS-232适合本地设备之间的通信，传输距离一般不超过20m。而RS-485的传输距离为几十米到上千米。

3、RS-232 只允许一对一通信，而RS-485 接口在总线上是允许连接多达128个收发器。

这些区别其实不是特别重要，因为一般移动开发一般遇到软件APP对接外部硬件设备，需要用的外部第三方设备的通讯协议，USB，232或而485协议进行交互通讯。

关于RS-485项目

首先我遇到的是安卓主板和外接的现金纸币机的交互，是这样一个需求：软件通过后台发来的socket指令，要求用户使用现金纸币支付订单（火车站，地铁，投入现金买票等场景），通过现金纸币机的验钞，计算现金额度，传输给软件进行找零计算，通过接口反馈到云端后台进行确认，开启其他权限操作。因为没有485串口线，所以采购量一根usb转串口，线里需要额外的芯片

usb转串口，通讯485模式

com.github.mik3y：usb-serial-for-android:3.3.0（具体可以详细查看）

首先是获取设备的属性权限

broadcastReceiver = new BroadcastReceiver() {@Overridepublic void onReceive(Context context, Intent intent) {if (intent.getAction().equals(INTENT_ACTION_GRANT_USB)) {usbPermission = intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)? UsbPermission.Granted : UsbPermission.Denied;connect();}}
};
mainLooper = new Handler(Looper.getMainLooper());

private void connect() {//连接UsbDevice device = null;UsbManager usbManager = (UsbManager) getActivity().getSystemService(Context.USB_SERVICE);for (UsbDevice v : usbManager.getDeviceList().values())if (item != null) {if (v.getDeviceId() == item.getDevice().getDeviceId()) {device = v;}}if (device == null) {status("连接失败:未找到设备");return;}UsbSerialDriver driver = UsbSerialProber.getDefaultProber().probeDevice(device);if (driver == null) {driver = CustomProber.getCustomProber().probeDevice(device);}if (driver == null) {status("连接失败:设备没有驱动程序");return;}if (driver.getPorts().size() < item.getPort()) {status("连接失败:设备上没有足够的端口");return;}usbSerialPort = driver.getPorts().get(item.getPort());UsbDeviceConnection usbConnection = usbManager.openDevice(driver.getDevice());if (usbConnection == null && usbPermission == UsbPermission.Unknown && !usbManager.hasPermission(driver.getDevice())) {usbPermission = UsbPermission.Requested;PendingIntent usbPermissionIntent = PendingIntent.getBroadcast(getActivity(), 0, new Intent(INTENT_ACTION_GRANT_USB), 0);usbManager.requestPermission(driver.getDevice(), usbPermissionIntent);return;}if (usbConnection == null) {if (!usbManager.hasPermission(driver.getDevice()))status("连接失败:权限被拒绝");elsestatus("连接失败:打开失败");return;}try {usbSerialPort.open(usbConnection);usbSerialPort.setParameters(baudRate, 8, 1, UsbSerialPort.PARITY_NONE);if (withIoManager) {usbIoManager = new SerialInputOutputManager(usbSerialPort, this);Executors.newSingleThreadExecutor().submit(usbIoManager);}status("连接");connected = true;} catch (Exception e) {status("连接失败: " + e.getMessage());disconnect();}
}

*/
@Override
public void onNewData(byte[] data) {//类似心跳操作+接收字节流接收操作runOnUiThread(() -> {receive(data);});
}

@Override
public void onRunError(Exception e) {//类似关流mainLooper.post(() -> {disconnect();});
}

private void send(String str) {//发送指令，485 以16进制转btye[]发送Log.e("tag", "------------请求指令-----:" + str);if (!connected) {Toast.makeText(getActivity(), "未连接", Toast.LENGTH_SHORT).show();return;}try {byte[] data = hexToByteArray(str);usbSerialPort.write(data, WRITE_WAIT_MILLIS);} catch (Exception e) {onRunError(e);}
}

private void disconnect() {connected = false;//  controlLines.stop();if (usbIoManager != null)usbIoManager.stop();usbIoManager = null;try {if (usbSerialPort != null) {usbSerialPort.close();}} catch (IOException ignored) {}usbSerialPort = null;
}

public static byte[] hexToByteArray(String inHex) {int hexlen = inHex.length();byte[] result;if (hexlen % 2 == 1) {//奇数hexlen++;result = new byte[(hexlen / 2)];inHex = "0" + inHex;} else {//偶数result = new byte[(hexlen / 2)];}int j = 0;for (int i = 0; i < hexlen; i += 2) {result[j] = hexToByte(inHex.substring(i, i + 2));j++;}return result;
}

private void send(String str) {Log.e("tag", "------------请求指令-----:" + str);if (!connected) {Toast.makeText(getActivity(), "未连接", Toast.LENGTH_SHORT).show();return;}try {byte[] data = hexToByteArray(str);usbSerialPort.write(data, WRITE_WAIT_MILLIS);} catch (Exception e) {onRunError(e);}
}

另一个项目需要使用ETC天线进行扣费处理，232协议，一大堆国标接口协议。。。

提供一个Serial.cpp文件

#include <jni.h>
#include <termios.h>#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <string.h>
#include "android/log.h"static const char *TAG = "serial_port";
#define LOGI(fmt, args...) __android_log_print(ANDROID_LOG_INFO,  TAG, fmt, ##args)
#define LOGD(fmt, args...) __android_log_print(ANDROID_LOG_DEBUG, TAG, fmt, ##args)
#define LOGE(fmt, args...) __android_log_print(ANDROID_LOG_ERROR, TAG, fmt, ##args)static speed_t getBaudrate(jint baudrate) {switch (baudrate) {case 0:return B0;case 50:return B50;case 75:return B75;case 110:return B110;case 134:return B134;case 150:return B150;case 200:return B200;case 300:return B300;case 600:return B600;case 1200:return B1200;case 1800:return B1800;case 2400:return B2400;case 4800:return B4800;case 9600:return B9600;case 19200:return B19200;case 38400:return B38400;case 57600:return B57600;case 115200:return B115200;case 230400:return B230400;case 460800:return B460800;case 500000:return B500000;case 576000:return B576000;case 921600:return B921600;case 1000000:return B1000000;case 1152000:return B1152000;case 1500000:return B1500000;case 2000000:return B2000000;case 2500000:return B2500000;case 3000000:return B3000000;case 3500000:return B3500000;case 4000000:return B4000000;default:return -1;}
}extern "C" {JNIEXPORT jobject JNICALL
Java_com_sky_besthardtool_category_serialport_api_SerialPort_open(JNIEnv *env, jclass type,jstring path_, jint baudrate,jint flags) {const char *path = env->GetStringUTFChars(path_, 0);// TODOint fd;speed_t speed;jobject mFileDescriptor;/* Check arguments */{speed = getBaudrate(baudrate);if (speed == -1) {/* TODO: throw an exception */LOGE("Invalid baudrate");return NULL;}}/* Opening device */{jboolean iscopy;const char *path_utf = env->GetStringUTFChars(path_, &iscopy);LOGD("Opening serial port %s with flags 0x%x", path_utf, O_RDWR | flags);fd = open(path_utf, O_RDWR | flags);LOGD("open() fd = %d", fd);env->ReleaseStringUTFChars(path_, path_utf);if (fd == -1) {/* Throw an exception */LOGE("Cannot open port");/* TODO: throw an exception */return NULL;}}/* Configure device */{struct termios cfg;LOGD("Configuring serial port");if (tcgetattr(fd, &cfg)) {LOGE("tcgetattr() failed");close(fd);/* TODO: throw an exception */return NULL;}cfmakeraw(&cfg);cfsetispeed(&cfg, speed);cfsetospeed(&cfg, speed);if (tcsetattr(fd, TCSANOW, &cfg)) {LOGE("tcsetattr() failed");close(fd);/* TODO: throw an exception */return NULL;}}/* Create a corresponding file descriptor */{jclass cFileDescriptor = env->FindClass("java/io/FileDescriptor");jmethodID iFileDescriptor = env->GetMethodID(cFileDescriptor, "<init>", "()V");jfieldID descriptorID = env->GetFieldID(cFileDescriptor, "descriptor", "I");mFileDescriptor = env->NewObject(cFileDescriptor, iFileDescriptor);env->SetIntField(mFileDescriptor, descriptorID, (jint) fd);}LOGD("Uart open succeed!!!");env->ReleaseStringUTFChars(path_, path);return mFileDescriptor;}JNIEXPORT void JNICALL
Java_com_sky_besthardtool_category_serialport_api_SerialPort_close(JNIEnv *env, jobject instance) {// TODOjclass SerialPortClass = env->GetObjectClass(instance);jclass FileDescriptorClass = env->FindClass("java/io/FileDescriptor");if (FileDescriptorClass == NULL) {LOGD("java/lang/ClassNotFoundException::java.io.FileDescriptor");}jfieldID mFdID = env->GetFieldID(SerialPortClass, "mFd", "Ljava/io/FileDescriptor;");if (mFdID == NULL) {LOGD("java/lang/NoSuchFieldException::FileDescriptor.readOnly(Z)");}jfieldID descriptorID = env->GetFieldID(FileDescriptorClass, "descriptor", "I");jobject mFd = env->GetObjectField(instance, mFdID);jint descriptor = env->GetIntField(mFd, descriptorID);LOGD("close(fd = %d)", descriptor);close(descriptor);
}
}

CmakeList.txt文件配置

# For more information about using CMake with Android Studio, read the
# documentation: https://d.android.com/studio/projects/add-native-code.html# Sets the minimum version of CMake required to build the native library.cmake_minimum_required(VERSION 3.4.1)# Creates and names a library, sets it as either STATIC
# or SHARED, and provides the relative paths to its source code.
# You can define multiple libraries, and CMake builds them for you.
# Gradle automatically packages shared libraries with your APK.add_library( # Sets the name of the library.serial_port# Sets the library as a shared library.SHARED# Provides a relative path to your source file(s).src/main/cpp/Serial.cpp )# Searches for a specified prebuilt library and stores the path as a
# variable. Because CMake includes system libraries in the search path by
# default, you only need to specify the name of the public NDK library
# you want to add. CMake verifies that the library exists before
# completing its build.find_library( # Sets the name of the path variable.log-lib# Specifies the name of the NDK library that# you want CMake to locate.log )# Specifies libraries CMake should link to your target library. You
# can link multiple libraries, such as libraries you define in this
# build script, prebuilt third-party libraries, or system libraries.target_link_libraries( # Specifies the target library.serial_port# Links the target library to the log library# included in the NDK.${log-lib} )

public class TransferManager {private static TransferManager instance;private SerialPort serialPort;private FileInputStream inputStream;public FileOutputStream outputStream;private ReadThread mReadThread;private OnIOTransferListener listener;private TransferManager() {}public static TransferManager getInstance() {if (instance == null) {synchronized (TransferManager.class) {if (instance == null) {instance = new TransferManager();}}}return instance;}public void connect(Context context) {String com = SpUtil.getCom(context);int baudRate = SpUtil.getBaudrate(context);try {serialPort = new SerialPort(com, baudRate);inputStream = (FileInputStream) serialPort.getInputStream();outputStream = (FileOutputStream) serialPort.getOutputStream();mReadThread = new ReadThread();mReadThread.start();} catch (Exception e) {listener.onSerialConnect(false);e.printStackTrace();}}public void disConnect() {if (mReadThread != null) {mReadThread.interrupt();mReadThread = null;}try {if (inputStream != null) {inputStream.close();inputStream = null;}if (outputStream != null) {outputStream.close();outputStream = null;}} catch (IOException e) {e.printStackTrace();}if (serialPort != null) {serialPort.close();}}private class ReadThread extends Thread {public void run() {int nMaxBufLength = 64;byte[] buffer = new byte[nMaxBufLength];while (!isInterrupted()) {try {int byteRead;Thread.sleep(50);if (inputStream != null) {byteRead = inputStream.read(buffer);if (byteRead >= 0) {if (listener != null) {byte[] sendBytes = new byte[byteRead];System.arraycopy(buffer, 0, sendBytes, 0, byteRead);listener.onReceive(sendBytes, byteRead);}}} else {
//                        P("mInputStream==null");break;}} catch (IOException e) {
//                    P("IOException");if (listener != null) {listener.onSerialConnect(false);}break;} catch (InterruptedException e) {
//                    P("InterruptedException");e.printStackTrace();}}//while(!isInterrupted())}}public void setOnIOTransferListener(OnIOTransferListener listener) {this.listener = listener;}}

完整的demo已经上传制github了

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Android基于串口通讯笔记（USB，485协议,232协议）

波特率

数据位

停止位

奇偶校验位

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