[USRP-users] timed commands

Nuria Ibrahim nuria_rhmet at yahoo.com
Tue Feb 26 09:11:20 EST 2013


Dear Mr Josh




	
	
	
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I have written a piece of code to test
timed-commands.
My application implements two threads 
the  first thread to tune USRP periodically every 1.5 seconds from
now and the second thread to display the overall receiving  chain
frequency  that is to observe whether the tuning takes place in the
desired time. below is the implementation of timed-command for timed
tuning of the USRP






	
	
	
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usrp->set_time_now(uhd::time_spec_t(0.0));

MAList=[3, 7,33, 45, 80, 85, 94,103]
usrp->set_rx_freq(936.4e6); 
//setting beacon channel



while(i<8)
{ 

		
			 int MAIO =(i%8);
			 arfcn=MAList[MAIO];
			 if(arfcn>=1 &&
arfcn<=124)
			 {
				 

				hope_freq=(935+ .2*arfcn)*1e6 ;
			 }
		
			//hopping from cord
						
			 uhd::tune_request_t
tune_req(hope_freq);	//retune USRP	
			
tune_req.rf_freq_policy=uhd::tune_request_t::POLICY_NONE;	
		const uhd::time_spec_t tune_time =
usrp->get_time_now() +    uhd::time_spec_t(1.5);



                                   
usrp->set_command_time(tune_time);	
			      tune_res = 
usrp->set_rx_freq(tune_req);			
			  usrp->clear_command_time();
			 

                                
while(usrp->get_time_now()<tune_time)
		       {
			      cout<<"do nothing
and wait to prevent premature tuning"<<endl;
		       }
			



			 i++;
		 }



now my expectation when I run this
program was, to get @ least 1.5 second time difference between
successive tune requests, unfortunately the result shows some early
tuning  










 













   







Actual RX Freq after hopping:
935.600000 Mhz... at time: 1.50161
Actual RX Freq after hopping:
935.600000 Mhz... at time: 1.50222
Actual RX Freq after hopping:
935.600000 Mhz... at time: 1.50258
Actual RX Freq after hopping:
936.400000 Mhz... at time: 1.50298   ->unexpected
Actual RX Freq after hopping:
936.400000 Mhz... at time: 3.00306
Actual RX Freq after hopping:
936.400000 Mhz... at time: 3.00352
Actual RX Freq after hopping:
941.600000 Mhz... at time: 3.00409    ->unexpected
Actual RX Freq after hopping:
941.600000 Mhz... at time: 4.50418
Actual RX Freq after hopping:
941.600000 Mhz... at time: 4.50488
Actual RX Freq after hopping:
941.600000 Mhz... at time: 4.50526
Actual RX Freq after hopping:
944.000000 Mhz... at time: 6.00517
Actual RX Freq after hopping:
944.000000 Mhz... at time: 6.00578  

Actual RX Freq after hopping:
944.000000 Mhz... at time: 6.00615
Actual RX Freq after hopping:
951.000000 Mhz... at time: 6.00655     ->unexpected
Actual RX Freq after hopping:
951.000000 Mhz... at time: 7.50661 

Actual RX Freq after hopping:
951.000000 Mhz... at time: 7.5071
Actual RX Freq after hopping:
951.000000 Mhz... at time: 7.50769
Actual RX Freq after hopping:
952.000000 Mhz... at time: 9.00758 

Actual RX Freq after hopping:
952.000000 Mhz... at time: 9.00821
Actual RX Freq after hopping:
952.000000 Mhz... at time: 9.00858
Actual RX Freq after hopping:
953.800000 Mhz... at time: 9.00897    ->unexpected
Actual RX Freq after hopping:
953.800000 Mhz... at time: 10.5088
Actual RX Freq after hopping:
953.800000 Mhz... at time: 10.5093 

Actual RX Freq after hopping:
953.800000 Mhz... at time: 10.5097
Actual RX Freq after hopping:
953.800000 Mhz... at time: 10.5101
Actual RX Freq after hopping:
955.600000 Mhz... at time: 10.5105     ->unexpected
Actual RX Freq after hopping:
955.600000 Mhz... at time: 12.0105 

Actual RX Freq after hopping:
955.600000 Mhz... at time: 12.011






what do you think is the problem?
Please help me here cause in real-time
hopping such kind  of premature tuning  result in synchronization
problem with BTS



Thanks in advance! 



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