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bindings.cpp
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bindings.cpp
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#include <jni.h>
#include <stdio.h>
#include <linux/fb.h>
#include <sys/ioctl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <stdlib.h>
extern "C" {
JNIEXPORT jdouble JNICALL
Java_edu_umich_PowerTutor_components_OLED_getScreenPixPower(
JNIEnv * env, jobject thiz, jdouble rcoef, jdouble gcoef,
jdouble bcoef, jdouble modul_coef);
}
#define NUMBER_OF_SAMPLES 500
static int fd = -2;
static struct fb_fix_screeninfo screeninfo;
static unsigned char* buf;
static unsigned int samples[NUMBER_OF_SAMPLES];
JNIEXPORT jdouble JNICALL
Java_edu_umich_PowerTutor_components_OLED_getScreenPixPower(
JNIEnv * env, jobject thiz, jdouble rcoef, jdouble gcoef,
jdouble bcoef, jdouble modul_coef) {
if(fd == -1) {
return (jdouble)-1.0;
} else if(fd == -2) {
fd = open("/dev/graphics/fb0", O_RDWR);
if(fd == -1) {
fd = open("/dev/fb0", O_RDWR);
}
if(fd == -1) {
return (jdouble)-1.0;
}
if(ioctl(fd, FBIOGET_FSCREENINFO, &screeninfo)) {
close(fd);
fd = -1;
return (jdouble)-1.0;
}
buf = (unsigned char*)mmap(NULL, screeninfo.smem_len, PROT_READ,
MAP_SHARED, fd, 0);
if(buf == (unsigned char*)-1) {
close(fd);
fd = -1;
return (jdouble)-1.0;
}
int range = screeninfo.smem_len / 12;
srand(555);
for(int i = 0; i < NUMBER_OF_SAMPLES; i++) {
int a = range * i / NUMBER_OF_SAMPLES;
int b = range * (i + 1) / NUMBER_OF_SAMPLES;
if(b <= a + 1) {
samples[i] = a;
} else {
samples[i] = a + rand() % (b - a);
}
}
}
jdouble pixPower = 0.0;
for(int i = 0; i < NUMBER_OF_SAMPLES; i++) {
int x = 4 * samples[i];
int r = buf[x];
int g = buf[x + 1];
int b = buf[x + 2];
/* Calculate the power usage of this one pixel if it were at full
* brightness. Linearly scale by brightness to get true power
* consumption. To calculate whole screen compute average of sampled
* region and multiply by number of pixels.
*/
int modul_val = r + g + b;
pixPower += rcoef * (r * r) + gcoef * (g * g) + bcoef * (b * b) -
modul_coef * (modul_val * modul_val);
}
return pixPower;
}