android应用程序访问I2C接口

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I2C总线是一种简单、双向二线制同步串行总线。它只需要两根线即可在连接于总线上的器件之间传送信息。
主器件用于启动总线传送数据，并产生时钟以开放传送的器件，此时任何被寻址的器件均被认为是从器件．在总线上主和从、发和收的关系不是恒定的，而取决于此时数据传送方向。如果主机要发送数据给从器件，则主机首先寻址从器件，然后主动发送数据至从器件，最后由主机终止数据传送；如果主机要接收从器件的数据，首先由主器件寻址从器件．然后主机接收从器件发送的数据，最后由主机终止接收过程。在这种情况下．主机负责产生定时时钟和终止数据传送。

Java code

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package xxxxxxx.xx;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

public class I2cRadioTest extends Activity {
    private static final String TAG = "I2cRadioTest";

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        int[] buf = new int[4];
        int slaveAddr = 0xXX;
        int fileHander;
        int mode = 0xXX | 0xXX;
        int i;

        I2c i2c = new I2c();
        fileHander = i2c.open("/dev/i2c-1");

        i2c.read(fileHander, slaveAddr, buf, 4);

        Log.w(TAG,
                "buf0= " + Integer.toHexString(buf[0]) + " buf1= "
                        + Integer.toHexString(buf[1]) + " buf2= "
                        + Integer.toHexString(buf[2]) + " buf=3 "
                        + Integer.toHexString(buf[3]));

        buf[0] = 0x01;
        i = 0;// i2c.write(fileHander, slaveAddr, mode, buf, 1);
        Log.w(TAG, "write length " + i);

        for (int j = 0; j < 4; j++) {
            buf[i] = 0;
        }

        i2c.read(fileHander, slaveAddr, buf, 4);
        Log.w(TAG,
                "buf0= " + Integer.toHexString(buf[0]) + " buf1= "
                        + Integer.toHexString(buf[1]) + " buf2= "
                        + Integer.toHexString(buf[2]) + " buf=3 "
                        + Integer.toHexString(buf[3]));

        i2c.close(fileHander);

        if ((buf[0] & 0x10) == 0x01) {
            Log.w(TAG, "------success-----");
        } else {
            Log.w(TAG, "----fail-------");
        }

        setContentView(R.layout.main);
    }
}
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package xxxxxx.xxx;

/**
 * This is a I2C operation class
 */
public class I2c {
    /**
     * @param nodeName
     *            node path name
     * @return return file hander else return <0 on fail
     */
    public native int open(String nodeName);

    /**
     * @param fileHander
     * @param i2c_adr
     *            slave addr
     * @param buf
     * @param Lenth
     *            of buf
     * @return read length
     */
    public native int read(int fileHander, int i2c_adr, int buf[], int Length);

    /**
     * @param fileHander
     * @param i2c_adr
     *            slave addr
     * @param sub_adr
     *            sub addr
     * @param buf
     * @param Lenth
     *            of buf
     * @return write length
     */
    public native int write(int fileHander, int i2c_adr, int sub_adr,
            int buf[], int Length);

    public native void close(int fileHander);

    static {
        System.loadLibrary("test-i2c");
    }
}

C/C++ code

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/* DO NOT EDIT THIS FILE - it is machine generated */
#include <jni.h>
/* Header for class xxxxxx_xxx_I2c */
#include <stdio.h>
#include <android/log.h>
#include <fcntl.h>
#include <linux/i2c.h>
#include <memory.h>
#include <malloc.h>

#ifndef _Included_xxxxxx_xxx_I2c
#define _Included_xxxxxx_xxx_I2c
#ifdef __cplusplus
extern "C" {
#endif
/*
 * Class:     xxxxxx_xxx_I2c
 * Method:    open
 * Signature: (Ljava/lang/String;)I
 */
JNIEXPORT jint JNICALL Java_xxxxxx_xxx_I2c_open
  (JNIEnv *, jobject, jstring);

/*
 * Class:     xxxxxx_xxx_I2c
 * Method:    read
 * Signature: (II[II)I
 */
JNIEXPORT jint JNICALL Java_xxxxxx_xxx_I2c_read
  (JNIEnv *, jobject, jint, jint, jintArray, jint);

/*
 * Class:     xxxxxx_xxx_I2c
 * Method:    write
 * Signature: (III[II)I
 */
JNIEXPORT jint JNICALL Java_xxxxxx_xxx_I2c_write
  (JNIEnv *, jobject, jint, jint, jint, jintArray, jint);

/*
 * Class:     xxxxxx_xxx_I2c
 * Method:    close
 * Signature: (I)V
 */
JNIEXPORT void JNICALL Java_xxxxxx_xxx_I2c_close
  (JNIEnv *, jobject, jint);

#ifdef __cplusplus
}
#endif
#endif
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#include "test-i2c.h"

#define  LOG_TAG    "i2c"
#define  LOGI(...)  __android_log_print(ANDROID_LOG_INFO,LOG_TAG,__VA_ARGS__)
#define  LOGE(...)  __android_log_print(ANDROID_LOG_ERROR,LOG_TAG,__VA_ARGS__)

JNIEXPORT jint JNICALL Java_xxxxxx_xxx_I2c_open
  (JNIEnv *env, jobject obj, jstring file)
  {
      char fileName[64];
      const jbyte *str;
      
      str = (*env)->GetStringUTFChars(env, file, NULL);
      if (str == NULL) {
          LOGI("Can't get file name!");
          return -1;
      }
      sprintf(fileName, "%s", str);
    LOGI("will open i2c device node %s", fileName);
      (*env)->ReleaseStringUTFChars(env, file, str);
      return open(fileName, O_RDWR);
  }
  
JNIEXPORT jint JNICALL Java_xxxxxx_xxx_I2c_read
  (JNIEnv * env, jobject obj, jint fileHander, jint slaveAddr, jintArray bufArr, jint len)
  {
      jint *bufInt;
      char *bufByte;
      int res = 0, i = 0, j = 0;
      
      if (len <= 0) {
          LOGE("I2C: buf len <=0");
          goto err0;
      }
      
      bufInt = (jint *) malloc(len * sizeof(int));
      if (bufInt == 0) {
          LOGE("I2C: nomem");
          goto err0;
      }
      bufByte = (char*) malloc(len);
      if (bufByte == 0) {
          LOGE("I2C: nomem");
          goto err1;
      }
      
      (*env)->GetIntArrayRegion(env, bufArr, 0, len, bufInt);
      
      res = ioctl(fileHander, I2C_SLAVE, slaveAddr);
      if (res != 0) {
          LOGE("I2C: Can't set slave address");
          goto err2;
      }
      
      memset(bufByte, '\0', len);
      if ((j = read(fileHander, bufByte, len)) != len) {
        LOGE("read fail in i2c read jni i = %d buf 4", i);
        goto err2;        
    } else {
        for (i = 0; i < j ; i++)
            bufInt[i] = bufByte[i];
        LOGI("return %d %d %d %d in i2c read jni", bufByte[0], bufByte[1], bufByte[2], bufByte[3]);
        (*env)->SetIntArrayRegion(env, bufArr, 0, len, bufInt);
    }
    
    free(bufByte);
    free(bufInt);
    
    return j;

err2:
    free(bufByte);
err1:
    free(bufInt);
err0:
    return -1;                                          
  }
  
JNIEXPORT jint JNICALL Java_xxxxxx_xxx_I2c_write
  (JNIEnv *env, jobject obj, jint fileHander, jint slaveAddr, jint mode,
   jintArray bufArr, jint len)
  {
      jint *bufInt;
      char *bufByte;
      int res = 0, i = 0, j = 0;
      
      if (len <= 0) {
          LOGE("I2C: buf len <=0");
          goto err0;
      }
      
      bufInt = (jint *) malloc(len * sizeof(int));
      if (bufInt == 0) {
          LOGE("I2C: nomem");
          goto err0;
      }
      bufByte = (char*) malloc(len + 1);
      if (bufByte == 0) {
          LOGE("I2C: nomem");
          goto err1;
      }
      
      (*env)->GetIntArrayRegion(env, bufArr, 0, len, bufInt);
      bufByte[0] = mode;
      for (i = 0; i < len; i++)
          bufByte[i + 1] = bufInt[i];      
      
      res = ioctl(fileHander, I2C_SLAVE, slaveAddr);
      if (res != 0) {
          LOGE("I2C: Can't set slave address");
          goto err2;
      }
      
      if ((j = write(fileHander, bufByte, len + 1)) != len + 1) {
        LOGE("write fail in i2c");
        goto err2;        
    }
    
    LOGI("I2C: write %d byte", j);
    free(bufByte);
    free(bufInt);
    
    return j - 1;

err2:
    free(bufByte);
err1:
    free(bufInt);
err0:
    return -1;     
  }
  
JNIEXPORT void JNICALL Java_xxxxxx_xxx_I2c_close
  (JNIEnv *env, jobject obj, jint fileHander)
  {
      close(fileHander);
  }

https://www.jianshu.com/p/02dc4bb83c95