On 09/05/2018 07:06 AM, RizThon wrote:
Thanks again Marcus,
Just to be clear, when you say I can stream at 56MS/s on a single
channel, is it in sc16, sc12 or sc8?
Over USB3, it shouldn't matter, except that in reality, on an actual
computer, with an actual controller, and actual operating system,
the bandwidth that the host machine is being asked to handle does matter.
Furthermore it matters *A LOT* exactly what your host machine is doing
with the samples. Discarding them is less work than just writing them
to a file, which is less work than doing DSP operations on them, etc,
etc.
I tried on a different machine, with i7-8550U and 8 or 16GB of RAM.
On Windows, I'm getting the same as before, ie lots of overflows, with
rx_samples_to_file.exe.
On Linux (from the Gnu Radio Live Environment), I installed UHD v3.13.0.1,
With rx_samples_to_file, I still can't choose sc12:
Error: LookupError: KeyError: Cannot find a conversion routine for
conversion ID
Input format: sc12_item32_le
Num inputs: 1
Output format: sc16
Num outputs: 1
What does that mean exactly? The B210 can send the data over USB in
sc12, but then UHD doesn't have a method to convert to sc16?
Is this a limitation to rx_samples_to_file, or I'll get the same error
if I make my own C++ program?
It may be the case that there isn't a converter from sc12 to sc16 within
UHD. My tests were all done with floating-point on the host side.
I also tried benchmark_rate. In random mode, I have no overflow in
sc8, but in sc16 I have lots of overflows and error messages. Without
the random mode, I can go up to 36MS/s in sc16, and 56MS/s in sc12! So
for some reason it seems I can use sc12 with benchmark_rate but not
rx_samples_to_file. I'm a bit loss.
That just means that the implementation of the random function on
Windows is probably rather slow.
I'm going to use an analogy here. Consider something like Niagara
Falls. It dumps however many billions of litres per hour over the side.
If your bucket isn't wide/deep enough, there's no way for you to
capture all of that. The USRP hardware is capable of 56Msps--it is the
Niagara Falls. Your computer is the bucket.
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