[andorid] realize SPI communication between kernel and app through JNI

about kernel Layer code ,Linux There is a classic reference driver in the original code , Can imitate spi drive .

If you don't ask too much , Just modify the equipment number and node name , Then you can talk to dts If the match is successful , Finally, remember to modify the generated node permissions

path：kernel/drivers/spi/spidev.c

diff --git a/device/rockchip/common/ueventd.rockchip.rc b/device/rockchip/common/ueventd.rockchip.rc
index 8d5d28d..4b6ac2a 100644
--- a/device/rockchip/common/ueventd.rockchip.rc
+++ b/device/rockchip/common/ueventd.rockchip.rc
@@ -65,6 +65,8 @@
 /dev/ttyS2                     0666   system     system
 /dev/ttyS3                     0666   system     system
 
+/dev/thm36                     0666   system     system
+
 # for radio
 /dev/ttyUSB0                   0660   radio      radio
 /dev/ttyUSB1                   0660   radio      radio

JNI Your code needs to be completed by yourself （ Unwanted HAL layer ）, And then JNI Add to App Chinese compiler .

The following code just realizes the simple read-write function , complete app and kernel Communication between , The complex part is the conversion between arrays .

JNI file name ：thm36_jni.c

#include <jni.h>
#include <stdio.h>
#include <fcntl.h>
#include <stdlib.h>
#include <assert.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 = "thm36_jni";

#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)

#define DEV_NAME    "/dev/thm36"

static jint fd;

JNIEXPORT jint JNICALL Java_com_example_aaron_se_Thm36Native_thm36Open(JNIEnv *env, jclass clazz)
{
    LOGD("JNI spi open ... ...");
    
    fd = open(DEV_NAME, O_RDWR);
    if (fd < 0)
    {
        LOGD("open device fail!");
        return -1;
    }
    
    return 0;
}

JNIEXPORT void JNICALL Java_com_example_aaron_se_Thm36Native_thm36Close(JNIEnv *env, jclass clazz)
{
    LOGD("JNI spi close ... ...");
    
    close(fd);
}

JNIEXPORT jint JNICALL Java_com_example_aaron_se_Thm36Native_thm36Read(JNIEnv *env, jclass clazz, jbyteArray jread_arr, jint len)
{
    jbyte *array = NULL;
    jboolean *buf;
    int  i = 0;
    
    LOGD("JNI spi read ... ...");
    
    array = (*env)->GetByteArrayElements(env, jread_arr, NULL);
    if (array == NULL)
    {
        LOGD("JNI spi read: GetByteArrayElements faid!");
        return -1;
    }
    
    buf = (jboolean *)calloc(sizeof(*array), sizeof(jboolean));
    if (buf == NULL)
    {
        LOGD("JNI spi read: calloc fail!");
        return -1;
    }
    
    read(fd, buf, len);
    for (i=0; i<len; i++)
    {
        LOGD("JNI spi read: buf: %#x", *(buf + i));
        *(array + i) = (jchar)(*(buf + i));
    }
    
    (*env)->ReleaseByteArrayElements(env, jread_arr, array, 0);
    
    free(buf);
    
    return 0;
}

JNIEXPORT jint JNICALL Java_com_example_aaron_se_Thm36Native_thm36Write(JNIEnv *env, jclass clazz, jbyteArray jwrite_arr, jint len)
{
    jbyte *array = NULL;
    jboolean *buf;
    int i = 0;
    
    LOGD("JNI spi write ... ...");
    
    array = (*env)->GetByteArrayElements(env, jwrite_arr, NULL);
    if (array == NULL)
    {
        LOGD("JNI spi write: GetByteArrayElements fail!");
        return -1;
    }
    
    buf = (jboolean *)calloc(sizeof(*array), sizeof(jboolean));
    if(buf == NULL)
    {
        LOGD("JNI spi write: calloc fail!");
        return -1;
    }
    
    for(i = 0; i < len; i++)
    {
        *(buf + i) = (jboolean)(*(array + i));
        LOGD("JNI spi write: data : %#x\n",*(buf + i));
    }
    
    (*env)->ReleaseByteArrayElements(env, jwrite_arr, array, 0);
    
    write(fd, buf, len);
    
    free(buf);
    
    return 0;
}

Compile the file ：Android.mk

LOCAL_PATH := $(call my-dir)

include $(CLEAR_VARS)

TARGET_PLATFORM := android-3
LOCAL_MODULE    := thm36_jni
LOCAL_SRC_FILES := thm36_jni.c
LOCAL_LDLIBS    := -llog

include $(BUILD_SHARED_LIBRARY)

App The test code is also very simple , One is the main activity , One is with JNI link

MainActivity.java

// JNI The first part of the function name in should be the same as this 
package com.example.aaron.se;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

public class MainActivity extends AppCompatActivity implements View.OnClickListener{

    Thm36Native thm36 = new Thm36Native();
    byte[] tx = {(byte)0xAA, 0x00, 0x06, 0x00, (byte)0xCA, 0x00, 0x00, 0x00, 0x00, (byte)0xCA};
    byte[] rx = new byte[22];

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button btn = (Button) findViewById(R.id.btn);

        btn.setOnClickListener(MainActivity.this);
    }

    @Override
    public void onClick(View view) {
        switch (view.getId()) {
            case R.id.btn:
                thm36.thm36Open();
                thm36.thm36Write(tx, tx.length);
                thm36.thm36Read(rx, rx.length);
                thm36.thm36Close();
                break;

            default:
                break;
        }
    }
}

Thm36Native.java

package com.example.aaron.se;

import android.util.Log;

public class Thm36Native {

    private final String TAG = "Thm36Native";

    public native int thm36Open();
    public native void thm36Close();
    public native int thm36Read(byte[] buf, int len);
    public native int thm36Write(byte[] buf, int len);

    static {
        System.loadLibrary("thm36");
    }
}

Reference resources ：

LeeAaron - Blog Garden