[Discuss-gnuradio] RE: Timestamp value

[Ulrika Uppman]

Oops, the printuts seems to have been mosched together in the mail, here is 
that part once again:

ts_in = 1435221596, ts_last = 0, diff = 1435221596
ts_in = 2560802396, ts_last = 1435221596, diff = 1125580800
ts_in = 3367616092, ts_last = 2560802396, diff = 806813696
ts_in = 4174429788, ts_last = 3367616092, diff = 806813696
ts_in = 686341724, ts_last = 4174429788, diff = 806879232
ts_in = 1493155420, ts_last = 686341724, diff = 806813696
ts_in = 2283192156, ts_last = 1493155420, diff = 790036736
ts_in = 3090005852, ts_last = 2283192156, diff = 806813696
ts_in = 3896819548, ts_last = 3090005852, diff = 806813696
ts_in = 408731484, ts_last = 3896819548, diff = 806879232


> -----Original Message-----
> From: address@hidden 
> [mailto:address@hidden
>  On Behalf Of Ulrika Uppman
> Sent: Thursday, February 18, 2010 5:10 PM
> To: address@hidden
> Subject: [Discuss-gnuradio] Timestamp value
> 
> Hi,
> I wonder how the timestamps are being generated for each 
> ethernet-packet sent from the USRP2 to the host? My initial 
> idea about how it works was that timestamps are generated at 
> 100MHz (same as the samples) and then the timestamp 
> associated with the first sample in an ethernet data packet 
> will be put in the metadata which could then be unpacked in 
> the host. I then would assume that the next packet after the 
> first one will have a timestamp value that is proportional to 
> the number of samples per packet times the decimation rate. 
> However I get timestamp values that increase much much more 
> for each received packet, so I wonder if my idea of how 
> timestamps are generated is wrong?
> 
> I run the stable 3.2 version of gnuradio on Ubuntu 9.04 and I 
> have an USRP2 with the RFX2400. (I also was going to try the 
> gnuradio trunk but I got problems with building, see my other 
> post "Error on make from git development trunk"). I tried 
> both an old version of the fpga bin-file and one that I just 
> recently downloaded (but both gave the same result).
> 
> I put some printouts in usrp2_impl.cc in the 
> handle_data_packet function and the output when I run 
> rx_streaming_samples then looks like this: 
> ./rx_streaming_samples -f 2457e6 -d 16 -N 400 -v 
> ..............................................................
> .....................
> Daughterboard configuration:
>   baseband_freq=2456250000.000000
>        ddc_freq=-750000.000000
>   residual_freq=-0.016764
>        inverted=no
> 
> USRP2 using decimation rate of 16
> Receiving 400 samples
> 
> ts_in = 1435221596, ts_last = 0, diff = 1435221596 ts_in = 
> 2560802396, ts_last = 1435221596, diff = 1125580800 ts_in = 
> 3367616092, ts_last = 2560802396, diff = 806813696 ts_in = 
> 4174429788, ts_last = 3367616092, diff = 806813696 ts_in = 
> 686341724, ts_last = 4174429788, diff = 806879232 ts_in = 
> 1493155420, ts_last = 686341724, diff = 806813696 ts_in = 
> 2283192156, ts_last = 1493155420, diff = 790036736 ts_in = 
> 3090005852, ts_last = 2283192156, diff = 806813696 ts_in = 
> 3896819548, ts_last = 3090005852, diff = 806813696 ts_in = 
> 408731484, ts_last = 3896819548, diff = 806879232
> 
> Copy handler called 2 times.
> Copy handler called with 2968 bytes.
> 
> Elapsed time was 0.000 seconds.
> Packet rate was 100000 pkts/sec.
> Approximate throughput was 148.40 MB/sec.
> Total instances of overruns was 0.
> Total missing frames was 0.
> ..............................................................
> .....................
> 
> ts_in is the timestamp found in the metadata of the packet 
> just received, ts_last is the one from previous packet and 
> diff is just the difference them between. Since there seems 
> to be no missing frames I'm guessing the big value of diff 
> can't be related to lost packets? 
> If I try different decimation rates, I see no obvious 
> relation between the difference in value between two timestamps...
> 
> Do anyone know why the difference in timestamp value between 
> received packets is so big? What am I missing here?
> 
> Thanks,
> /Ulrika
> 
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