由于链接
这个问题可能看起来很模糊，因此我已经为所提到的模块提供了代码片段。我编写了一个程序，它从I2C总线上的各种传感器收集数据，并将格式化的值存储在一个文件中。这应该由Xilinx在SoC配置中称为Zedboard的ARM cortex A9处理器（单核）运行，并将petalinux操作系统与vanilla linux内核一起使用。使用clock_gettime（）测量时间。我注意到，在单个进程中按顺序访问所有传感器时，单个传感器访问时间显着减少。此时间的比较是通过仅访问单个传感器的单个进程的比较完成的，并且不将数据写入文件，而是将其打印到stdout。
传感器与模块一起使用：
GY521模块：
#include <linux/i2c-dev-user.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdint.h>
#include <inttypes.h>
#include "GY521.h"
#include <time.h>
#define ADDR 0x68
static int file;
static __s32 res;
static __u8 reg;
static __u8 values[14]; //array to hold all the register values
void set_sleep_gy521(int flag)
{
if(flag==0) //wake up the device
{
//Accessing reg 107
reg = 0x6B;
uint8_t val8 = 0x01; //write 0x00 if you want to set the internal 8MHz oscillator as CLK
res = i2c_smbus_write_byte_data(file, reg, val8);
if(res<0)
perror("Failed to wake it up");
/*else
printf("Device is awake\n");*/
}
else //set it to sleep
{
reg = 0x6B;
uint8_t val8 = 0x41; //write 0x40 if you want to set the internal 8MHz oscillator as CLK
res = i2c_smbus_write_byte_data(file, reg, val8);
if(res<0)
perror("Failed to go to sleep");
/*else
printf("In sleep mode\n");*/
}
}
void init_gy521()
{
char filename[20];
int adapter_no = 0;
snprintf(filename, 19, "/dev/i2c-%d", adapter_no);
file = open(filename, O_RDWR);
if(file<0)
{
perror("File not opened");
exit(1);
}
if(ioctl(file, I2C_SLAVE, ADDR)<0)
{
perror("Not able to access the device");
exit(EXIT_FAILURE);
}
//setting the sensitivity of the gyroscope and accelerometer
res = i2c_smbus_write_byte_data(file, 0x1B, 0x00);
if(res<0)
perror("Failed to set gyro range");
res = i2c_smbus_write_byte_data(file, 0x1C, 0x00);
if(res<0)
perror("Failed to set the accelerometer range");
set_sleep_gy521(0); //this also sets the clock source to X-axis gyro reference which is slightly better than the internal 8MHz oscillator
}
//get_values() stores all the register measurements in the array values
int get_values()
{
//reading all the values needed at once in a block
res = i2c_smbus_read_i2c_block_data(file, 0x3B, 14, (__u8*)values);
if(res<0)
perror("Failed to read using Block");
return res;
}
float get_Ax()
{
int c = get_values(); //calls get_values() to get all values at a time instant
int16_t xout;
if(c>0)
xout = (((int16_t)values[0])<<8) | values[1];
else
{
perror("Can't get the values");
exit(EXIT_FAILURE);
}
return xout/16384.0*9.8;
}
float get_Ay()
{
//concatenate the higher byte and the lower byte
int16_t yout = (((int16_t)values[2])<<8) | values[3];
return yout/16384.0*9.8;
}
float get_Az()
{
int16_t zout = (((int16_t)values[4])<<8) | values[5];
return zout/16384.0*9.8;
}
float get_temp_gy521()
{
__s16 temp = (((int16_t)values[6])<<8) | values[7];
return (temp/340.0 + 36.53);
}
float get_Wx()
{
__s16 xgyro = (((int16_t)values[8])<<8) | values[9];
return xgyro/131.0;
}
float get_Wy()
{
__s16 ygyro = (((int16_t)values[10])<<8) | values[11];
return ygyro/131.0;
}
float get_Wz()
{
__s16 zgyro = (((int16_t)values[12])<<8) | values[13];
return zgyro/131.0;
}
void clear_gy521()
{
close(file);
}
int main()
{
struct timespec start, end;
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start);
init_gy521();
printf("Wx: %f\n", get_Wx());
printf("Wy: %f\n", get_Wy());
printf("Wz: %f\n", get_Wz());
printf("Ax: %f\n", get_Ax());
printf("Ay: %f\n", get_Ay());
printf("Az: %f\n", get_Az());
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end);
printf("Time taken by GY521 is %d MuS\n", (end.tv_sec-start.tv_sec)*1000000L+(end.tv_nsec-start.tv_nsec)/1000);
}
LM75模块：
#include <linux/i2c-dev-user.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include <time.h>
#define ADDRESS 0x48
static int file; //use static keyword to ensure that the scope of this variable is limited to this file.
static __u8 buffer[2];
int get_temp()
{
if(i2c_smbus_read_i2c_block_data(file, 0x00, 2, buffer)<0)
perror("Failed to read the block");
return buffer[0]&127;
}
//Initializes the file used by the userspace calls. [IMPORTANT] Must be run before any other function is called for this device!. This needs to be called only once for each process.
void init_LM75()
{
int adapter_number = 0; //check this.
char filename[20];
snprintf(filename, 19, "/dev/i2c-%d", adapter_number);
file = open(filename, O_RDWR);
if(file<0)
{
perror("File not opened");
exit(1);
}
if(ioctl(file, I2C_SLAVE, ADDRESS)<0)
{
perror("ioctl could not open file");
exit(1);
}
}
int main()
{
struct timespec start, end;
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start);
init_LM75();
printf("Temperature is %d\n", get_temp());
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end);
printf("Time taken %d\n", (end.tv_sec-start.tv_sec)*1000000L+(end.tv_nsec-start.tv_nsec)/1000);
}
HMC5883L模块：
#include <linux/i2c-dev-user.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <fcntl.h>
#include "HMC5883L.h"
#include <time.h>
#define ADDRESS 0x1e
static int file; //use static keyword to ensure that the scope of this variable is limited to this file.
static float factor;
static __u8 buffer[6];
//register addresses
__u8 config_reg_A = 0x00;
__u8 mode_reg = 0x02;
__u8 gain_reg = 0x01;
__u8 data_X_H = 0x03;
__u8 data_X_L = 0x04;
__u8 data_Y_H = 0x07;
__u8 data_Y_L = 0x08;
__u8 data_Z_H = 0x05;
__u8 data_Z_L = 0x06;
/**
* The value of mode must be according to the following table:
* Value Mode
* 0 Continuous
* 1 Single (Default)
* 2 Idle
* 3 Idle
*
* After any mode change care must be taken to set it back to continuous mode before reading any values.
**/
void set_magnetometer_mode(int mode)
{
__u8 value = 0x00;
value |= mode;
if(i2c_smbus_write_byte_data(file, mode_reg, value)<0)
perror("Failed to change magnetometer mode");
}
void get_B()
{
if(i2c_smbus_read_i2c_block_data(file, data_X_H, 6, buffer)<0)
perror("Failed to read the block");
}
//[IMPORTANT] Note that the following 3 functions will return the field values in milli gauss by reading them from the buffer. So call get_Bx() first!
float get_Bx()
{
get_B();
int16_t temp;
//concatenate the upper and lower bits
temp = buffer[0];
int16_t b_X = (temp<<8) | buffer[1];
return (float)b_X*factor;
}
float get_By()
{
int16_t temp;
//concatenate the upper and lower bits
temp = buffer[4];
int16_t b_Y = (temp<<8) | buffer[5];
return (float)b_Y*factor;
}
float get_Bz()
{
int16_t temp;
//concatenate the upper and lower bits
temp = buffer[2];
int16_t b_Z = (temp<<8) | buffer[3];
return (float)b_Z*factor;
}
//Initializes the file used by the userspace calls. [IMPORTANT] Must be run before any other function is called for this device!. This needs to be called only once for each process.
void init_magnetometer()
{
int adapter_number = 0; //check this.
char filename[20];
snprintf(filename, 19, "/dev/i2c-%d", adapter_number);
file = open(filename, O_RDWR);
if(file<0)
{
perror("File not opened");
exit(1);
}
if(ioctl(file, I2C_SLAVE, ADDRESS)<0)
{
perror("ioctl could not open file");
exit(1);
}
factor = 0.92;
set_magnetometer_mode(0);
}
void clear_magnetometer()
{
close(file);
}
/**
* The value of freq must be according to the following table:
* Value Rate (Hz)
* 0 0.75
* 1 1.5
* 2 3
* 3 7.5
* 4 15 (Default)
* 5 30
* 6 75
**/
void set_magnetometer_frequency(int freq)
{
__u8 value = 0x00;
value |= freq<<2;
if(i2c_smbus_write_byte_data(file, config_reg_A, value)<0)
perror("Failed to change data rate");
}
/**
* The value of gain must be according to the following table:
* Value Field Range (+/- Gauss)
* 0 0.88
* 1 1.3 (Default)
* 2 1.9
* 3 2.5
* 4 4.0
* 5 4.7
* 6 5.6
* 7 8.1
*
* This function will also set the value of the factor to be multiplied to the raw data.
**/
void set_magnetometer_gain(int gain)
{
__u8 value = 0x00;
value |= gain<<5;
if(i2c_smbus_write_byte_data(file, gain_reg, value)<0)
perror("Failed to change magnetometer gain");
else
{
switch(gain)
{
case 0: factor = 0.73; break;
case 1: factor = 0.92; break;
case 2: factor = 1.22; break;
case 3: factor = 1.52; break;
case 4: factor = 2.27; break;
case 5: factor = 2.56; break;
case 6: factor = 3.03; break;
case 7: factor = 4.35; break;
}
}
}
int main()
{
struct timespec start, end;
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start);
init_magnetometer();
printf("%f\t%f\t%f\n", get_Bx(), get_By(), get_Bz());
clear_magnetometer();
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end);
printf("Time taken by HMC is %d MuS\n", (end.tv_sec-start.tv_sec)*1000000L+(end.tv_nsec-start.tv_nsec)/1000);
}
单个模块，将所有三个模块连接在一起，并将数据写入文件：
#include <stdio.h>
#include <stdlib.h>
#include "hwfunctions.h"
#include <time.h>
int main()
{
struct timespec start_hk, end_hk, start_hmc, end_hmc, start_gy, end_gy, start_lm, end_lm;
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start_hk);
char *finalstr = (char* ) malloc(50);
FILE *f = fopen("fullhk.txt", "a");
if(f==NULL)
{
perror("Couldn't open file\n");
exit(0);
}
//initialization of the three sensors
//init_gy80();
time_t curt;
time(&curt);
//fseek(f, 0, SEEK_END);
sprintf(finalstr, "Time: %s\n", ctime(&curt));fputs(finalstr, f);
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start_hmc);
init_magnetometer();
sprintf(finalstr, "Bx: %f\n", get_Bx());fputs(finalstr, f);
sprintf(finalstr, "By: %f\n", get_By());fputs(finalstr, f);
sprintf(finalstr, "Bz: %f\n", get_Bz());fputs(finalstr, f);
clear_magnetometer();
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end_hmc);
sprintf(finalstr, "S1: %f\n", get_S1());fputs(finalstr, f);
sprintf(finalstr, "S2: %f\n", get_S2());fputs(finalstr, f);
sprintf(finalstr, "S3: %f\n", get_S3());fputs(finalstr, f);
sprintf(finalstr, "S4: %f\n", get_S4());fputs(finalstr, f);
sprintf(finalstr, "S5: %f\n", get_S5());fputs(finalstr, f);
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start_lm);
init_LM75();
sprintf(finalstr, "Temperature: %d\n", get_temp());fputs(finalstr, f);
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end_lm);
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &start_gy);
init_gy521();
sprintf(finalstr, "Wy: %f\n", get_Wy());fputs(finalstr, f);
sprintf(finalstr, "Wz: %f\n", get_Wz());fputs(finalstr, f);
sprintf(finalstr, "Ax: %f\n", get_Ax());fputs(finalstr, f);
sprintf(finalstr, "Ay: %f\n", get_Ay());fputs(finalstr, f);
sprintf(finalstr, "Az: %f *end of block*\n\n", get_Az());
clear_gy521();
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end_gy);
fputs(finalstr, f);
fclose(f);
//closing the three sensors
//clear_gy80();
free(finalstr);
clock_gettime(CLOCK_PROCESS_CPUTIME_ID, &end_hk);
printf("Time taken by single hmc instance: %ld microseconds\n", (end_hmc.tv_sec-start_hmc.tv_sec)*1000000L + (end_hmc.tv_nsec-start_hmc.tv_nsec)/1000);
printf("Time taken by single gy instance: %ld microseconds\n", (end_gy.tv_sec-start_gy.tv_sec)*1000000L + (end_gy.tv_nsec-start_gy.tv_nsec)/1000);
printf("Time taken by single lm instance: %ld microseconds\n", (end_lm.tv_sec-start_lm.tv_sec)*1000000L + (end_lm.tv_nsec-start_lm.tv_nsec)/1000);
printf("Time taken by single housekeeping instance: %ld microseconds\n", (end_hk.tv_sec-start_hk.tv_sec)*1000000L + (end_hk.tv_nsec-start_hk.tv_nsec)/1000);
}
管家是单个模块的名称，管家输出上方的输出是针对各个传感器模块的。管家模块已经编译并与没有主功能的传感器模块链接，并且在交叉编译期间使用了O2优化标志。即使CLOCK_BOOTTIME测量时间包含内核优先权，时间上的差异也是相同的。
如果需要更多信息来揭穿这个谜团，请发表评论！
1 个答案:
答案 0 :(得分：1)
当你第一次使用库函数时，我会怀疑后台发生了什么。
尝试禁用延迟绑定，例如，通过设置环境变量$ ./readLBL.sh science.txt
Text read from file science.txt: 58050364;Tom Jones
Text read from file science.txt: 58050365;Marry Jane
（Is there a linker flag to force it to load all shared libraries at start time?）
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