linux延时函数

#include <unistd.h>
 
   1、unsigned int sleep(unsigned int seconds); 秒级
   2、int usleep(useconds_t usec);              微秒级：1/10^-6
 
   #define _POSIX_C_SOURCE 199309
   #include <time.h>
   3、int nanosleep(const struct timespec *req, struct timespec *rem);
       struct timespec {
                  time_t tv_sec;       
                  long   tv_nsec;      
              };
       // The value of the nanoseconds field must be in the range 0 to 999999999.
 
 内核层：
   include <linux/delay.h>
   1、void ndelay(unsigned long nsecs);         纳秒级：1/10^-10
   2、void udelay(unsigned long usecs);         微秒级: 1/10^-6
   3、void mdelay(unsigned long msecs);         毫秒级：1/10^-3