Hi Jonathan, Thank you for the detailed response (which I read after replying to Homin - doh). We already have our ROACH-1 here and are trying to keep costs down so I'm going to push ahead a little more with trying to figure out if we can get this to work with a ROACH-1 and 1:2 ADCs. I do have a couple of questions/points though before I ask to borrow the 1:2 boards.
1) The nominal plan would be to run 2 channels at 5GSa/s, 4bit on a ROACH-1- i.e. using 2 ADC boards. My understanding is the the ROACH-1 in practice should be ok to do this (depending on number of channels etc in the PFB) 2) Am I being very naive (I suspect I am) in thinking that with some work (but not a total rewrite) I could just take the correlator tutorial, replace the ADC and with the yellow block for the 1x5000-8 boards and tweek the number of channels in the PFB (we don't need many at all which should help fitting on the VIRTEX 5). If 1+2 are within the bounds of sanity then it might be worth trying to see if we can get this up and running - We can always fall back to the 3.6 GS/s if it's proving to be a nightmare. I'll check out the memo and website too. Cheers, Ross On Tue, Mar 12, 2013 at 7:37 AM, Jonathan Weintroub <jweintr...@cfa.harvard.edu> wrote: > Hi Ross, > > I am commenting this older thread prompted by your most recent message re > DMUX1:2 ADCs, to which Homin responded today. > > Your approach, and the advice received from Dan and Glenn, is sound---in > principal. With suitable bit codes, you can run DMUX1:2 4-bit versions of > the ASIAA ADC at full rate, in dual channel 2.5 GSa/s mode, hosted on a > ROACH1. And with two ADC boards installed you can enable four such 2.5 GSa/s > input channels on ROACH1. Whether the ROACH1 can process the four channels > with Virtex 5 resources of course depends on what you want to do, Dan gave > one benchmark. We have a PFB resource utilization memo which may be able to > help you. > > There is a caveat, however: my group is among a few CASPER collaborators who > are doing wideband correlator design using ASIAA 5 GSa/s ADCs. We decided > some time ago to standardize on using the 8-bit DMUX 1:1 version of the ADC > supported by ROACH2. In our case we without question needed the > computational resources of Virtex6-SX475, so the higher GPIO interface speed > (translates to Z-DOK speed) in some sense came for free. Though we could > probably meet our requirements with fewer than 8-bits, there was no penalty > for enabling them by using the DMUX1:1 board. > > A consequence of this is that all our developments and contributions to the > CASPER open source infrastructure support this configuration (8-bit and > ROACH2). In brief we have contributed yellow block work, ADC > characterization, and resource calculations for PFBs. Now, we are not the > only ones doing this kind of work, and much of what we do is probably > transferable to the ROACH1 and 4-bit case. However, at least from my biased > perspective, you may find the ROACH2 8-but case to be better supported, and > thus the hardware cost savings through using ROACH1 may prove to be false > economy. The 4-bit and 8-bit ADCs are equal in cost. > > (By the way the 8-bit ADC board can be used on ROACH1 but you would be > limited to 1.8 GSa/s per channel or 3.6 GSa/s per ADC board.) > > All that said, I have a few DMUX1:2 ADCs sitting in the lab fully assembled, > working, and unused, and I would be happy to loan these to you. Actually > they probably belong to Homin / ASIAA, so I guess subject to his ok. > > Our wideband developments are documented on a public Wiki: > > https://www.cfa.harvard.edu/twiki/bin/view/SMAwideband > > Dig down for ADC characterization and our resource memo. > > Cheers, stay in touch. > > Jonathan Weintroub > CfA > +1-617-495-7319 > > > > On Feb 12, 2013, at 4:09 PM, Ross Williamson wrote: > >> Hi Dan and Glenn, >> >> All sounds good - I think have the ROACH-1 design will help us out a lot >> here to get started. We really don't need a very high spectral response as >> we are just trying to measure the amplitude and phase of a PSFs wings >> referenced to the central core of the PSF. >> >> Cheers, >> >> Ross >> >> On Tue, Feb 12, 2013 at 1:05 PM, G Jones <glenn.calt...@gmail.com> wrote: >> Note that the design Dan is referring to currently has only been >> tested to ~1.5 GHz BW. Getting to higher bandwidths will likely >> require some work to meet timing. Also the data comes out over 10 >> gigabit Ethernet so requires something to catch the data. >> >> On Tue, Feb 12, 2013 at 4:02 PM, Dan Werthimer <d...@ssl.berkeley.edu> wrote: >> > >> > hi ross, >> > >> > how many frequency channels do you need in your two input correlator? >> > >> > we have a full stokes VEGAS 1K channel spectrometer design >> > that uses a pair of ADC08-5000's. >> > (a full stokes spectrometer is the same thing as a two input correlator) >> > >> > our current design is for roach2, but we had tested working designs >> > for roach1 last year, and we can probably dig these up. >> > >> > best wishes, >> > >> > dan >> > >> > >> > On Tue, Feb 12, 2013 at 12:53 PM, Ross Williamson >> > <rwilliam...@astro.caltech.edu> wrote: >> >> >> >> Hi All, >> >> >> >> I'm new to CASPER/ROACH boards and so apologies if this is obvious. We >> >> are hoping to build a simple 2-channel correlator with a fairly high >> >> bandwidth. We are in the process of ordering a ROACH-1 board and I was >> >> thinking of also purchasing the ADC1X5000-8 ADC - A few questions: >> >> >> >> 1) Should I even be looking at an ADC1X5000-8 for use as a correlator? >> >> 2) I believe I need the DMUX 1:2 version to work with ROACH-1 board - is >> >> that correct? >> >> 3) I should be able to run 2 channels at 2.5GHz 4bits with a single board >> >> - correct? >> >> 4) If I wanted to could I purchase another ADC1X5000-8 and try and run >> >> with 5GHz bandwidth on each channel using the ROACH-1? >> >> >> >> Best regards, >> >> >> >> Ross >> >> >> >> -- >> >> Ross Williamson >> >> Research Scientist - Sub-mm Group >> >> California Institute of Technology >> >> 626-395-2647 (office) >> >> 312-504-3051 (Cell) >> > >> > >> >> >> >> -- >> Ross Williamson >> Research Scientist - Sub-mm Group >> California Institute of Technology >> 626-395-2647 (office) >> 312-504-3051 (Cell) > -- Ross Williamson Research Scientist - Sub-mm Group California Institute of Technology 626-395-2647 (office) 312-504-3051 (Cell)
