Re: [casper] Spectrum woes

[Andrew Vdb]

Hi all,

We (SKA-SA) saw similar behaviour with our PFB and found it was a
combination of things - one being to *not* select BRAM optimisations, and
another was a bug in the coefficient use in the PFB. Give the
ska-sa/mlib_deve l repo a spin - we
pushed our fixes a few months back.

Andrew

On Mon, Sep 19, 2016 at 1:00 AM, Jack Hickish  wrote:

> Hi Michael,
>
> Hmmm. Can you link the repo you're using and a reference design?
>
> Thanks
> Jack
>
> On Sun, 18 Sep 2016 at 15:05 Michael D'Cruze  manchester.ac.uk> wrote:
>
>> Hi Jack,
>>
>>
>>
>> To implement the change in optimisation I altered the delay_bram init
>> script. Line 84 which configures the Xilinx ram block, I changed the
>> parameter ‘optimize’ from ‘Area’ to ‘Speed’. No other changes were made,
>> so, I think this is the former case?
>>
>> BW
>> Michael
>>
>>
>>
>> *From:* Jack Hickish [mailto:jackhick...@gmail.com]
>> *Sent:* 18 September 2016 22:27
>> *To:* Michael D'Cruze; casper@lists.berkeley.edu
>> *Subject:* Re: [casper] Spectrum woes
>>
>>
>>
>> Hi Michael,
>>
>>
>>
>> Is this actually the optimisation parameter of the xilinx bram block, or
>> an optimisation of a casper block which completely changes some underlying
>> circuit (eg by doing a bunch of fanout control and instantiating multiple
>> small brams instead of one big one)?
>>
>> If the latter, are you sure it's not a bug in the casper implementation?
>> Perhaps a mismatch of latency on various things being fanned out?
>>
>>
>>
>> Trust nothing.
>>
>>
>>
>> Jack
>>
>>
>>
>> On Sun, 18 Sep 2016 at 14:21 Michael D'Cruze > manchester.ac.uk> wrote:
>>
>> Dear all,
>>
>>
>>
>> I’ve been chasing the cause of some nasty artefacts in my spectra
>> recently. The first turned out to be a known bug in the Xilinx compiler,
>> activated when the BRAM_sharing optimisation in the FFT is checked, however
>> the artefacts I’m seeing since seem to be activated by the RAM blocks in
>> the delay_bram block being configured for “Speed”, and not the default
>> “Area”.
>>
>>
>>
>> Below are links to two spectra. They were both recorded from the Lovell
>> telescope’s L-band receiver while the telescope was pointing at the zenith.
>> The logic used in both cases is identical, with the exception that the
>> delay_brams in the first spectra are configured for Speed, and in the
>> second they are configured for Area (default). All operating parameters
>> were the same in both cases.
>>
>>
>>
>> https://dl.dropboxusercontent.com/u/38103354/figure_1.png
>>
>> https://dl.dropboxusercontent.com/u/38103354/r13a_libs_18-09_2207.PNG
>>
>>
>>
>> Aside from how ugly the first spectrum looks (there are signals in there
>> which simply don’t exist), even the accumulated power is different. The
>> vertical scale is logarithmic so this is a factor 100 or so higher with the
>> brams configured for Speed. I don’t understand how they could be so
>> different, nor why configuring the brams for Speed should make any
>> difference at all, not least a difference of this magnitude.
>>
>>
>>
>> The most worrying thing for me now is that configuring the brams for
>> Speed was key to getting my larger designs (16k and 32k channels) to meet
>> timing. If I need to reconfig for Area, I’m going to have to brawl with Par
>> and PlanAhead all over again… It actually took a few goes to get just that
>> 4k channel design to compile.
>>
>>
>>
>> I’d appreciate ideas/suggestions!
>>
>> Thanks
>>
>> Michael
>>
>>
>>
>>
>>
>>


-- 
Dr Andrew van der Byl

Mobile: +27 83 312 7392
Email: a vd...@gmail.com

Re: [casper] casper Digest, Vol 90, Issue 10

[Andrew Vdb]

Hi all,

For those interested in White Rabbit, Xilinx have an article in their Xcell
journal (91). The link is here
http://issuu.com/xcelljournal/docs/xcell_journal_issue_91/18?e.

regards,
Andrew

On Thu, May 7, 2015 at 1:45 AM, casper-requ...@lists.berkeley.edu wrote:

 Send casper mailing list submissions to
 casper@lists.berkeley.edu

 To subscribe or unsubscribe via the World Wide Web, visit

 https://calmail.berkeley.edu/manage/list/listinfo/casper@lists.berkeley.edu

 or, via email, send a message with subject or body 'help' to
 casper-requ...@lists.berkeley.edu

 You can reach the person managing the list at
 casper-ow...@lists.berkeley.edu

 When replying, please edit your Subject line so it is more specific
 than Re: Contents of casper digest...


 Today's Topics:

1. Re: Timing distribution over fiber (Jack Hickish)


 --

 Message: 1
 Date: Wed, 06 May 2015 23:45:53 +
 From: Jack Hickish jackhick...@gmail.com
 Subject: Re: [casper] Timing distribution over fiber
 To: Johan Burger jbur...@ska.ac.za, Michael Inggs
 miki...@gmail.com,Bob Stricklin bstr...@n5brg.com, Sias
 Malan
 s...@ska.ac.za,   Renier Siebrits ren...@ska.ac.za,
 Francois Kapp
 franc...@ska.ac.za,   Etienne Bauermeister etie...@ska.ac.za
 Cc: Simon Lewis simonacle...@hotmail.com, Casper Lists
 casper@lists.berkeley.edu,Thomas Abbott tabb...@ska.ac.za,
 Stephan Sandenberg ssandenbe...@gmail.com
 Message-ID:
 CAG1GKS=5fWeJ+quOj=
 gj_rd7qgtngc2z_07abtx7nwjhojw...@mail.gmail.com
 Content-Type: text/plain; charset=utf-8

 On Wed, 6 May 2015 at 07:35 Johan Burger jbur...@ska.ac.za wrote:

 
  Hi there,
 
  Do you maybe have any idea of requirement specifications for the HERA's
 RF
  phase stability and time (?) - this might determine what technology could
  be appropriate.
 

 Hi Johan,

 Thanks for your response. We're sampling at 500 MHz, so we'd like to have a
 stability of few degrees, preferably over timescales of many hours but
 perhaps more reasonably on a calibration cadence of O(10 minutes)

 PPS is not such a big deal, and synchronization to a couple of ADC clock
 cycles is probably fine. We're investigating simple-ish ways to calibrate
 these out with signal injection.



 
  We at SKA Africa have after some iteration come up, with a precision RF
  distribution system for many antennas.  The type of laser and integrated
  modulator have been proven in the field on large arrays (not just
  MeerKAT).  The RF can be directly transmitted (in our case up to 2-3 GHz
  limited by our synthesizer - the precise frequency is 1.712GHz).  500MHz
 RF
  over fibre can be done by this as well.  There is conditioning of the RF
  taking place on MeerKAT at the receiving end. As Jason said, not any or
 all
  modules really do the job properly - we converged on a solution after
  testing, that implicitly included modules evaluated from KAT-7 days, and
  more recent modules from other manufacturers.
 
  Low precision timing ~100ns can indeed be done using PTP.  If PPS is
  required instead of an Ethernet package a special conversion board (PCIe)
  is necessary.  This is really enough for fringe finding - used in MeerKAT
  S-band for example. That digitiser is mounted in an RFI shielded pedestal
  of the antenna though.  We supply the high precision PPS using our custom
  system as described below.
 
  For our L-band digitisers mounted on the outside we had to come up with
  special low power, low cost, high accuracy solution - this is being
  implemented by Renier and Etienne and others here at SKA Africa (so a
 joint
  effort by our time and frequency and digitiser team).  The reason is that
  White Rabbit is not compatible with 10Gbe links used on this system.
  Furthermore Ethernet is actually quite noisy as per MeerKAT measurements,
  and White Rabbit and PTP uses that (and with highish power consumption
 and
  largish board size), and is not preferable in a high purity clock signal
  and PPS module.  We found that measurement based PPS system will meet our
  requirements though, for stabilized links and provides us with accurate
  absolute time references at antennas, using analog methodologies.  This
 for
  example being important in pulsar science.
 
  I am not sure what level of RFI shielding you would be able to mount
  around modules, but as said RFI from Ethernet has certainly been found to
  be an RFI culprit, and cannot be therefore be used in MeerKAT close to
  sensitive modules - and needs to separately shielded.  This therefore
 means
  that if PPS is generated from White Rabbit/PTP there is still some
  uncertain propagation paths left (important at least for MeerKAT) up to
 the
  point of digitization where a timing edge is inserted.  We are using
  seperate fibres for PPS and RF, to further limit self-RFI and as it was
  found that requirements could only be met 

[casper] Signal Processing Workshop: Live Streaming

[Andrew Vdb]

Hi All,

Just an update - we are experiencing some technical issues with the live
stream. It should come back online shortly.


Regards
Andrew

[casper] Signal Processing Workshop

[Andrew Vdb]

Hi everyone,

This is just to inform that the signal processing workshop taking place in
Cape Town at the University of Cape Town (28th to 31st January) will be
streamed online each day. Please visit  (
https://sites.google.com/site/hpdspworkshopcpt2012/) and use the link
provided to log in and view. A programme is also available online so you
can see what talks will be given and the associated time slot. All times
shown are relative to South Africa (GMT+2).

Regards,
Andrew