[USRP-users] USRP1 and UHD rx_samples_to_file

Josh Blum josh at joshknows.com
Thu Nov 11 18:17:27 EST 2010


> It seems like most of the UHD examples were written with the USRP2 in mind.

Many of examples were written to support the full time stamping 
capabilities of USRP2, and eventually future products, making USRP1 the 
odd man out.

>
> Using rx_samples_to_file with USRP1 gives:
> Error: unsupported stream command type for USRP1
>
> (so there is no out-of-the-box working rx app for USRP1?)
>

See the tx waveforms and ascii art dft :-)

> It looks like USRP1 doesn't support STREAM_MODE_NUM_SAMPS_AND_DONE. Is there
> a hardware reason for this, or has it just not been backported yet? Is there
> a rough ETA on it's development, if it's possible?
>
> In general, which UHD features will not (ever) be available to USRP1? Will
> timestamping/metadata stuff ever make it?
>

Timestamping is not supported by the hardware. There is a alternative 
FPGA image floating around with time-stamping capabilities. Its not 
quite sufficient, but if a usrp-enthusiast wanted to take on porting 
this to the UHD, it would definitely be accepted into the mainline code.

Practically, if timestamping is implemented, it would not be as full 
featured as USRP2 for example because of FPGA size limitations.

> What would the downside be of using STREAM_MODE_START_CONTINUOUS in this RX
> app?
>

That would work. I think the idea was to demonstrate requesting a 
specific number of samples. But you could just as easily read until n 
samples and then turn off streaming. With the first method (when 
applicable) you know that your queues are empty when all the samples 
have arrived. In the latter you will want to drain the rx queue before 
starting streaming again.

-Josh




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