mjhjmtu

Working on a embedded Linux device built using yocto that is pulling a date via uart from another device with a satellite connection. By the time we have access to this date, we are well into a fully initialized multi-threaded application as well as various daemons running etc.

From what I have read, using stime() or settimeofday() can result in breaking anything relying on timers. I'm guessing that something like std::this_thread::sleep_for() would be included in this?

Is there a safe way to set the system time at this point or how do most embedded Linux devices that do not have internet access navigate this problem?

Edit: We do have an RTC but the implementation of hwclock we are using does not allow us to directly write to it, at least through the hwclock api. Here is the --help:

BusyBox v1.24.1 (2018-11-14 12:40:41 PST) multi-call binary. 
Usage: hwclock [-r|--show] [-s|--hctosys] [-w|--systohc] [-t|--systz] [-l|--localtime] [-u|--utc] [-f|--rtc FILE]

And the link to the hwclock source.

You can use hwclock which should be built into every embedded linux distro.

$hwclock is - as the command name suggest - a hardware clock, independent of the OS being used. These days it uses a low-power oscillator built into the motherboard, that tracks the passage of time even when the machine is powered down (uses mb battery that will last a long time)

If hwclock is not available, there are other alternatives which I will gladly go over, but hwclock should be your goto command if available.

My solution was to write directly to the rtc using ioctrl. Here's an implementation for anyone who comes across this:

#include <linux/rtc.h>
#include <stdio.h>
#include <fcntl.h>
#include <sys/ioctl.h>


int main(void)

 int fd;
 fd = open("/dev/rtc0",0);
 if (fd < 0)
 printf("Can't open rtc!");

 struct rtc_time time;

 time.tm_sec = 12;
 time.tm_min = 12;
 time.tm_hour = 7;
 time.tm_mday = 12;
 time.tm_mon = 7;
 time.tm_year = 118;

 if (ioctl(fd, RTC_SET_TIME, &time) < 0 )
 printf("Set rtc failed!");

 return 0;