Brian,
I am not sure what the issue is here. I don't think it is the chained DDC
anymore as I can see the issue with the single DDC using multiple different
bitfiles.
I wasn't re-tuning the Fc anywhere, I was just dropping the sample rate from
120MHz down to something I could handle. Right now I am not touching the
CORDIC modifications at all.
What version of UHD are you running for your applications?
--------- Original Message --------- Subject: Re: [USRP-users] Can I use
chained DDCs?
From: "Brian Padalino" <bpadal...@gmail.com>
Date: 12/3/18 11:44 am
To: "Jason Matusiak" <ja...@gardettoengineering.com>
Cc: "USRP-users@lists.ettus.com" <usrp-users@lists.ettus.com>
On Mon, Dec 3, 2018 at 11:32 AM Jason Matusiak via USRP-users
<usrp-users@lists.ettus.com> wrote:
Actually, upon further review, I can get this to happen with the stock XG
image and as simple flowgraph as possible.
If I run the stock image as non-RFNoC seems to be fine, so it has something to
do with me using RFNoC.
I tried switing to HG, but I see the same issues.
Has anyone else experienced this? I find it hard to believe that this is
happening for everyone else, but I can't figure out why it would happen with
the stock image. My specs are:
[INFO] [UHD] linux; GNU C++ version 4.8.5 20150623 (Red Hat 4.8.5-28);
Boost_105300; UHD_4.0.0.rfnoc-devel-702-geec24d7b
--------- Original Message --------- Subject: Can I use chained DDCs?
From: "Jason Matusiak" <ja...@gardettoengineering.com>
Date: 12/3/18 7:23 am
To: "Ettus Mail List" <usrp-users@lists.ettus.com>
I have a flowgraph where I use 3 different DDCs on an X310. There is a dual
DDC that is connected to the two radios on the X310. Then I have 2 single DDCs
chained off of that first one. I built these DDCs to only have a single
input/output on them.
The dual DDC still only has one AXI input port to it, so it can't handle 2
radios worth of stuff going into it. Right? This seems weird to me.
The flowgraph will work, but sometimes won't. What I see is that things
sometimes get tuned off center. I have a tone that I am putting out on a
different device, I fire up my flowgraph, and I see the tone in both paths
(that is an example, it doesn't always work on every first run). I stop the
flowgraph and run again. This time it may work, or it might be off-tuned. If
I re-tune the radio via Qt, I can see the signal elsewhere. Why would this be?
One more piece of information. When it is off-tuned, it isn't always the same
place. Sometimes it is only off by 100s of kHz, sometimes it is off my 10s of
MHz. This is VERY odd to me. Any advice?
I run a modified FPGA with a modified such that I have: Radio -> Single
Channel DDC -> Modified Multiple Output DDC -> Host, and I heavily utilize
changing the center frequencies of each of those DDC's. It works flawlessly.
In your RFNoC application, how are you changing that center frequency of the
downstream DDC's? Are you sure you've appropriately translated the frequency
to whatever new baseband from the first DDC?
Brian
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