Re: [Discuss-gnuradio] USRP2- Timestamp

[Marc Epard]

On Aug 3, 2010, at 8:42 PM, Ashish Bansal wrote:

I am using USRP2. The newer version of GNU 3.3 contains timestamp code. 

1. What do you exactly mean by timestamp. Does it mean it will output the 64 bit timer value with each sample. What is the command on the host side to see these timestamps.

2. How can I relate timestamp with ADC Samples.

3. I do see timestamp being used in the following files in USRP2 Firmware "app_common_v2.c", "txrx.c"  etc.  Are all the files loaded in the firmware by default or I have to change something.

I'm currently playing with timestamps. I'm using raw ethernet, rather than UHD in case that's what you mean by "newer".  The raw frames carry only a 32-bit timer.

You can find my current code at https://public.me.com/mepard. usrp2_streamper.cpp is a modification of gnuradio/usrp2/host/apps/rx_streaming_samples.cc. It'll scan a range of frequencies, capturing sample data and saving metadata for each frequency. The code relating to your question is in the BufferedHandler class.

I've also posted MATLAB code that reads the saved samples and metadata.  Currently, LoadGnuRadioIQ.m counts overflows, yielding a 64-bit timer. I'm planning to move that code to the C++.

One thing that puzzled me is the work-around that seems to be required to reconcile the timestamps and sample counts between the first and second frames. I've not yet looked deeper into the USRP2 code as the work-around seems to be effective.

Hope you find this useful. Naturally, any and all feedback, particularly bug reports, is welcome.

-Marc