Setting and Updating Absolute Time in Zephyr Application Using time_t Epoch

[Andrea Verdecchia]

I am trying to configure the absolute time in my application, which at some point receives the time_t epoch value from an external source and should update it internally so that at any time I can retrieve the actual epoch to use in my application. I have tried to update the epoch using the function

void Set_Time( time_t epochTime )
{
    int ret;
    struct timespec ts;

    ts.tv_sec = epochTime;
    ts.tv_nsec = 0;
    ret = clock_settime( CLOCK_REALTIME, &ts );

    if ( ret < 0 )
    {
        LOG_WRN( "clock_settime returned error" );
    }
}

and then read it through the function time(NULL), but the latter always returns the value -1. Does anyone have any suggestions for implementing what I want?

[Susheel Nuguru]

Does time(NULL) return -1 even if you do not call your function Set_Time()? 

I was thinking that it is better to maintain an epoch offset rather than trying to set the time itself, something like below

void Set_Time(time_t epochTime)
{
    epoch_offset = epochTime - (k_uptime_get() / 1000);
    LOG_INF("Time set to: %d (offset: %d)", epochTime, epoch_offset);
}


time_t Get_Time(void)
{
    return epoch_offset + (k_uptime_get() / 1000);
}

[Andrea Verdecchia]

Thank you for your response. In the meantime, I solved the issue by no longer using the time() function, which seemed to be linked to a different library than I had expected. I believe the -1 value was due to it not being initialized. I resolved the problem by implementing custom functions that use clock_settime() and clock_gettime().

void Set_Time( time_t epoch )
{
    int ret;
    struct timespec ts;

    ts.tv_sec = epoch;
    ts.tv_nsec = 0;
    ret = clock_settime( CLOCK_REALTIME, &ts );

    if ( ret < 0 )
    {
        LOG_WRN( "clock_settime returned error" );
    }
}

time_t Get_Time( void )
{
    struct timespec ts;
	int ret;

	ret = clock_gettime( CLOCK_REALTIME, &ts );

	if ( ret < 0 )
    {
		return (time_t) -1;
	}

	return ts.tv_sec;
}

This way, I can update and read the absolute epoch.

[Susheel Nuguru]

Sounds reasonable Andrea, thanks for letting us know.