G-Sensor

This guide explains how to identify the G-Sensor device node and read acceleration data from it using a C program.

Verify the G-Sensor device node exists:

$ ll /dev/accel 

Expected output:

crw-rw-rw- 1 root root 10, 50 Mar 18 12:17 /dev/accel

The following sample program demonstrates reading data from the G-Sensor using default settings. You can extend it to implement other functions.

gsensor_sample_data.c

#include <stdio.h>
#include <sys/ioctl.h>
#include <fcntl.h>
 
#define GBUFF_SIZE                12
#define GSENSOR_IOCTL_MAGIC       'a'
 
#define GSENSOR_IOCTL_INIT              _IO(GSENSOR_IOCTL_MAGIC, 0x01)
#define GSENSOR_IOCTL_RESET             _IO(GSENSOR_IOCTL_MAGIC, 0x04)
#define GSENSOR_IOCTL_CLOSE             _IO(GSENSOR_IOCTL_MAGIC, 0x02)
#define GSENSOR_IOCTL_START             _IO(GSENSOR_IOCTL_MAGIC, 0x03)
#define GSENSOR_IOCTL_GETDATA           _IOR(GSENSOR_IOCTL_MAGIC, 0x08, char[GBUFF_SIZE+1])
#define GSENSOR_IOCTL_APP_SET_RATE      _IOW(GSENSOR_IOCTL_MAGIC, 0x10, short)
#define GSENSOR_IOCTL_GET_CALIBRATION   _IOR(GSENSOR_IOCTL_MAGIC, 0x11, int[3])
 
 
struct sensor_axis {
    int x;
    int y;
    int z;
};
 
char *gsensor_device = "/dev/accel";
int gsensor_fd = -1;
 
int main(int argc, char **argv){
 
        struct sensor_axis gsensor_data;
 
        gsensor_fd = open(gsensor_device, O_RDWR);
 
        if (0 > gsensor_fd){
                printf("gsensor node open failed ...\n");
                exit(-1);
        }else{
                printf("gsensor node open success!!!\n");
        }
 
        if(ioctl(gsensor_fd, GSENSOR_IOCTL_START, NULL) == -1) {
                printf("gsensor start failed ... \n");
                close(gsensor_fd);
                exit(-1);
        }else{
                printf("gsensor start sueecss !!!\n");
        }
 
        printf("start to get gsensor data ...\n");
        while(1){
 
                if(ioctl(gsensor_fd, GSENSOR_IOCTL_GETDATA, &gsensor_data) == -1) {
                        printf("gsensor get data faile ... \n");
                        close(gsensor_fd);
                        exit(-1);
                }
 
                printf("gsensor_data -- x:%d,y:%d,z:%d \n", gsensor_data.x, gsensor_data.y, gsensor_data.z);
                sleep(1);
        }
        close(gsensor_fd);
 
		return 0;
}

Compile the program:

$ gcc -o gsensor_sample_demo gsensor_sample_demo.c

Run the compiled program. While it is running, tilt or move the board to observe changes in the acceleration values.

$ sudo ./gsensor_sample_demo
gsensor node open success!!!
gsensor start sueecss !!!
start to get gsensor data ...
gsensor_data -- x:-2112,y:16,z:16448
gsensor_data -- x:-2128,y:176,z:16128
gsensor_data -- x:-1632,y:2784,z:15968
gsensor_data -- x:7440,y:-3760,z:14608
gsensor_data -- x:-512,y:-7280,z:12128
gsensor_data -- x:-14384,y:-2336,z:11280
gsensor_data -- x:9952,y:-5264,z:15216
gsensor_data -- x:-6432,y:3760,z:24896