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Re: [Discuss-gnuradio] python/digital examples and UHD

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] python/digital examples and UHD
Date: Mon, 29 Nov 2010 09:47:14 -0500

On Mon, Nov 29, 2010 at 4:02 AM, Moritz Fischer
<address@hidden> wrote:
> Hash: SHA1
> Hi list,
> over the weekend I spend some time trying to update the demos to work
> with the UHD, I just started playing with git, so if you see something
> stupid let me know ;-)
> I put what I got on (in the uhd-examples branch):
> address@hidden:mfischer/gnuradio-mfischer.git
> However the part where it 'automagically' picks rx/tx bitrates is not
> really working as I have no idea how to detect what device I'm talking
> to. Also please note that as I don't have the right values for bitrates
> and samples_per_symbol don't be surprised if the examples crash ;-)
> The old generic_usrp.py had ranges for the possible decimation /
> interpolation factors as we don't have this in UHD I'm a bit confused on
> how to continue.
> I started to add a function
> samp_rate_range_t get_rx_samp_rate_range()
> to UHDs single_usrp_sink / multi_usrp_sink which internally would ask
> the corresponding _dev for the right ranges, depending on what device
> you're talking to. I still have to figure out the ranges part though.
> address@hidden:mfischer/uhd-mfischer.git
> As I don't really have insight into the longtime plan for UHD,
> I'm not sure whether that's the way to go though...
> Can someone give me any hints whether this actually makes sense?
> Happy hacking,
> - -Moritz

Thanks, Moritz. I'll try to take a look at this sometime.

Have you used the version 2 digital code, yet (benchmark_tx2,
benchmark_rx2, usrp_receive_path2, etc.)? One of the things I did was
include better resampling so that you can get any bit rate you want.
You still have to go through the process of selecting the USRP's
sample rate that's closest to your desired rate, and then the
resampling takes care of the rest.

What I do with the UHD driver is ask for a sample rate. It will then
set its sample rate to whatever the closest rate it can do. You can
the read back the actual sample rate of the USRP with get_samp_rate().
I then use this value to determine the difference between my desired
sample rate and the actual sample rate, which I then plug into the
arbitrary resampler.


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