JNI 呼叫C, 由C控制 DHT11讀取溫濕度 (完成版)

其實上次的錯誤有兩個原因, 那天躺到床上時, 忽然就想到了 XD

1. 權限問題, 要用  sudo java -Djava.library.path=. JavaDHT 來執行
2. 程式碼問題, 我忘記要先呼叫 bcm2835_init()

其他不多說, 看Code就行了....

	pi@raspberrypi ~/jni $ javac JavaDHT.java
	pi@raspberrypi ~/jni $ javah -jni JavaDHT
	pi@raspberrypi ~/jni $ gcc -I /opt/java/jdk1.7.0_21/include/ -I /opt/java/jdk1.7.0_21/include/linux/ JavaDHT.c -l bcm2835 -std=gnu99 -o JavaDHT
	pi@raspberrypi ~/jni $ sudo ./JavaDHT 11 15
	Using pin #15
	Data (40): 0x23 0x0 0x1a 0x0 0x3d
	Temp = 26 *C, Hum = 35 %
	Result Str: Temp = 26 *C, Hum = 35 %
	pi@raspberrypi ~/jni $ gcc -shared -I /opt/java/jdk1.7.0_21/include/ -I /opt/java/jdk1.7.0_21/include/linux/ JavaDHT.c -l bcm2835 -std=gnu99 -o libJavaDHT.so
	pi@raspberrypi ~/jni $ sudo java -Djava.library.path=. JavaDHT
	Data (40): 0x23 0x0 0x1a 0x0 0x3d
	Temp = 26 *C, Hum = 35 %
	result=Temp = 26 *C, Hum = 35 %

view raw Command Line hosted with ❤ by GitHub

	// How to access GPIO registers from C-code on the Raspberry-Pi
	// Example program
	// 15-January-2012
	// Dom and Gert
	//
	// Access from ARM Running Linux
	#define BCM2708_PERI_BASE 0x20000000
	#define GPIO_BASE (BCM2708_PERI_BASE + 0x200000) /* GPIO controller */
	#include <jni.h>
	#include <stdio.h>
	#include <string.h>
	#include <stdlib.h>
	#include <dirent.h>
	#include <fcntl.h>
	#include <assert.h>
	#include <unistd.h>
	#include <sys/mman.h>
	#include <sys/types.h>
	#include <sys/stat.h>
	#include <sys/time.h>
	#include <bcm2835.h>
	#include <unistd.h>
	#include "JavaDHT.h"
	#define MAXTIMINGS 100
	//#define DEBUG
	#define DHT11 11
	#define DHT22 22
	#define AM2302 22
	int readDHT(int type, int pin, char* result);
	int main(int argc, char **argv)
	{
	if (!bcm2835_init())
	return 1;
	if (argc != 3) {
	printf("usage: %s [11|22|2302] GPIOpin#\n", argv[0]);
	printf("example: %s 2302 4 - Read from an AM2302 connected to GPIO #4\n", argv[0]);
	return 2;
	}
	int type = 0;
	if (strcmp(argv[1], "11") == 0) type = DHT11;
	if (strcmp(argv[1], "22") == 0) type = DHT22;
	if (strcmp(argv[1], "2302") == 0) type = AM2302;
	if (type == 0) {
	printf("Select 11, 22, 2302 as type!\n");
	return 3;
	}
	int dhtpin = atoi(argv[2]);
	if (dhtpin <= 0) {
	printf("Please select a valid GPIO pin #\n");
	return 3;
	}
	printf("Using pin #%d\n", dhtpin);
	char theStr[] = "";
	readDHT(type, dhtpin, theStr);
	printf("Result Str: %s \n",theStr);
	return 0;
	} // main
	int bits[250], data[100];
	int bitidx = 0;
	JNIEXPORT jstring JNICALL
	Java_JavaDHT_readDHTfromC (JNIEnv *env, jobject obj, jint theType, jint thePin){
	char theStr[]="Call by Java_JavaDHT_readDHTfromC";
	bcm2835_init();
	readDHT(theType, thePin, theStr);
	jstring rtstr = (*env)->NewStringUTF(env, theStr);
	return rtstr;
	}
	int readDHT(int type, int pin, char* result) {
	int counter = 0;
	int laststate = HIGH;
	int j=0;
	// Set GPIO pin to output
	bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_OUTP);
	bcm2835_gpio_write(pin, HIGH);
	usleep(500000); // 500 ms
	bcm2835_gpio_write(pin, LOW);
	usleep(20000);
	bcm2835_gpio_fsel(pin, BCM2835_GPIO_FSEL_INPT);
	data[0] = data[1] = data[2] = data[3] = data[4] = 0;
	// wait for pin to drop?
	while (bcm2835_gpio_lev(pin) == 1) {
	usleep(1);
	}
	// read data!
	for (int i=0; i< MAXTIMINGS; i++) {
	counter = 0;
	while ( bcm2835_gpio_lev(pin) == laststate) {
	counter++;
	//nanosleep(1); // overclocking might change this?
	if (counter == 1000)
	break;
	}
	laststate = bcm2835_gpio_lev(pin);
	if (counter == 1000) break;
	bits[bitidx++] = counter;
	if ((i>3) && (i%2 == 0)) {
	// shove each bit into the storage bytes
	data[j/8] <<= 1;
	if (counter > 200)
	data[j/8] |= 1;
	j++;
	}
	}
	#ifdef DEBUG
	for (int i=3; i<bitidx; i+=2) {
	printf("bit %d: %d\n", i-3, bits[i]);
	printf("bit %d: %d (%d)\n", i-2, bits[i+1], bits[i+1] > 200);
	}
	#endif
	printf("Data (%d): 0x%x 0x%x 0x%x 0x%x 0x%x\n", j, data[0], data[1], data[2], data[3], data[4]);
	if ((j >= 39) &&
	(data[4] == ((data[0] + data[1] + data[2] + data[3]) & 0xFF)) ) {
	// yay!
	if (type == DHT11)
	printf("Temp = %d *C, Hum = %d \%\n", data[2], data[0]);
	sprintf(result, "Temp = %d *C, Hum = %d \%\n", data[2], data[0]);
	if (type == DHT22) {
	float f, h;
	h = data[0] * 256 + data[1];
	h /= 10;
	f = (data[2] & 0x7F)* 256 + data[3];
	f /= 10.0;
	if (data[2] & 0x80) f *= -1;
	printf("Temp = %.1f *C, Hum = %.1f \%\n", f, h);
	sprintf(result, "Temp = %.1f *C, Hum = %.1f \%\n", f, h);
	}
	return 1;
	}
	//result = "Error";
	return 0;
	}

view raw JavaDHT.c hosted with ❤ by GitHub

	/* DO NOT EDIT THIS FILE - it is machine generated */
	#include <jni.h>
	/* Header for class JavaDHT */
	#ifndef _Included_JavaDHT
	#define _Included_JavaDHT
	#ifdef __cplusplus
	extern "C" {
	#endif
	/*
	* Class: JavaDHT
	* Method: readDHTfromC
	* Signature: (II)Ljava/lang/String;
	*/
	JNIEXPORT jstring JNICALL Java_JavaDHT_readDHTfromC
	(JNIEnv *, jobject, jint, jint);
	#ifdef __cplusplus
	}
	#endif
	#endif

view raw JavaDHT.h hosted with ❤ by GitHub

	import java.lang.*;
	public class JavaDHT {
	public JavaDHT (){
	System.loadLibrary("JavaDHT");
	}
	public native String readDHTfromC (int theType, int thePin);
	/**
	* @param args
	*/
	public static void main(String[] args) {
	// TODO Auto-generated method stub
	String str = new JavaDHT().readDHTfromC(11,15);
	System.out.println("result=" + str);
	}
	}

view raw JavaDHT.java hosted with ❤ by GitHub