Sorry, I'm clocking the ADC at 800Mhz and therefore the FPGA at 200Mhz.
So the glitch occurs on every 2^21 clock cycles of the FPGA.
Jason Castro
NRAO
On 9/17/2012 2:47 PM, Jason Castro wrote:
Are we sick of Tutorial 3 yet??? I discovered yet another 25dB glitch
on a longer time scale. Again, I'm clocking the FPGA at 800Mhz. The
glitch occurs about every 63 seconds or 2^23 clock cycles. Here's
another link to a plot:
ftp://ftp.cv.nrao.edu/NRAO-staff/jcastro/CASPER/Spectrometer/Tutorial_3_glitching_60sec.PNG
Ideas??? This is turning into quite the learning experience!
Jason Castro
On 9/17/2012 1:03 PM, Jack Hickish wrote:
Hey Jason et al.
On 17 September 2012 16:31, Andrew Martens <and...@ska.ac.za
<mailto:and...@ska.ac.za>> wrote:
Slipping normally happens when the sync and data paths become
misaligned
leading to one being shorter, longer than the other. This would add
noise and cause frequencies to move around.
Cheers
Andrew
This was indeed the problem -- there is a bug in the sync_gen block
that doesn't properly set a comparator constant value. As a result,
the sync period was 2 clocks out (= 4 channels out because of
even/odd interleaving). I've fixed the sync_gen block's init script
and sent a pull request to the main casper repo.
I've also compiled a working model (just tested on an Oxford roach
with no obvious issues) which is in the tutorials_devel repo. The
boffile should be good straight out of the box, but if you're
recompiling the model make sure you have the sync_gen fix from the
casper library first (it is immediately available in the
casper_vanilla branch of https://github.com/oxfork/mlib_devel.git .
This (as opposed to the oxfork master branch) should merge into the
main casper repo without issue).
Hopefully that's Tutorial 3 sorted.....
On Mon, 2012-09-17 at 10:56 -0400, Jason Castro wrote:
> Thank you all for your input. It's always nice to come into
work on a
> Monday and be able to hit the ground running! I loaded Jack's
latest
> tutorial 3 bof file and I got some interesting results. The
spectrum
> slips along the x axis 4 channels every 800ms or so. This slipping
> event is also accompanied by about 10db of noise in the stop
band of the
> signal. Please see the following plots:
>
>
ftp://ftp.cv.nrao.edu/NRAO-staff/jcastro/CASPER/Spectrometer/Tutorial_3_sliding_spectrum1.PNG
>
ftp://ftp.cv.nrao.edu/NRAO-staff/jcastro/CASPER/Spectrometer/Tutorial_3_sliding_spectrum2.PNG
>
> I'll dive into this and try to figure out what's going on, but
extra
> eyes are appreciated.
>
> Thanks,
>
> Jason Castro
> NRAO
>
>
>
> On 9/17/2012 8:03 AM, Jason Manley wrote:
> > On 17 Sep 2012, at 11:45, Jack Hickish wrote:
> >> 2^27 isn't a valid sync period for tut3, which has an FFT
ending in a 10th order reorder
(https://casper.berkeley.edu/memos/sync_memo_v1.pdf).
> > Good catch! This is what I get for copy-pasting that design
from another :-/
> >
> > Tut3 has been in use in CASPER for over 3 years now and I
think you're the first one to notice!
> >
> > Jason
>
>
