How to get time from server

[Arcanum7]

Hi! I have sx1272 + stm32L072 and use loramac lib.
How can i get UTC time fom server on every TXRX frame by MAC commands?

[mluis1]

The LoRaWAN specification defines a MAC command named DeviceTimeReq/DeviceTimeAns.

Therefore in order to get the time from the Network Server the end-device needs to ask the execution of a DeviceTimeReq MAC command.

An example on how to do this can be found below

LoRaMac-node/src/apps/LoRaMac/common/LmHandler/LmHandler.c

Lines 520 to 539 in 05353ff

	static LmHandlerErrorStatus_t LmHandlerDeviceTimeReq( void )
	{
	LoRaMacStatus_t status;
	MlmeReq_t mlmeReq;
	mlmeReq.Type = MLME_DEVICE_TIME;
	status = LoRaMacMlmeRequest( &mlmeReq );
	LmHandlerCallbacks->OnMacMlmeRequest( status, &mlmeReq, mlmeReq.ReqReturn.DutyCycleWaitTime );
	DutyCycleWaitTime = mlmeReq.ReqReturn.DutyCycleWaitTime;
	if( status == LORAMAC_STATUS_OK )
	{
	return LORAMAC_HANDLER_SUCCESS;
	}
	else
	{
	return LORAMAC_HANDLER_ERROR;
	}
	}

Please note that the received time will be based on GPS epoch.
This code also provides the time as UTC based (without leap seconds).
You need to implement a way to convey the current number of leap seconds. If this is not implemented the time will be wrong by 27 seconds (as of today).

Your second sentence is confusing. You should not query for time at every transmission. You should do this only once in a while.