[Halld-tracking-hw] fADC125 FE firmware

[Gerard Visser]

Hi Cody,
	If the upsampling is done continuously then the processing has to be done in 
the frontend FPGA's, obviously you don't want to send 4-5x as much data over the 
daisy-chain to "processor" FPGA.
	Perhaps you will find that you can fit all the required processing in the 
frontend FPGA's. This would be nice, and would remove any concerns about the 
readout daisy-chain bandwidth. In this case it is simplest to upsample 
continuously. And probably to process on-the-fly (although you'll have to think 
how you will handle overlapping windows from closely spaced triggers, e.g. will 
need multiple copies of the integrator/accumulator).
	If that is not the plan, if you would put the processing in the "processor" 
FPGA and send raw samples from the frontend to the processor FPGA as was the 
original intention, then the upsampling needs to be done on a small region. I 
think this will be perfectly feasible... Upsampling just consists of replicating 
samples and then passing through an FIR filter so if the filter is short enough 
not many original samples are needed to fully prime the pipeline. Perhaps as 
little as 5 or so? Clearly the FIR coefficient vector needs to be chosen 
carefully. Naomi is probably (?) still using the original one that I calculated 
but a shorter one may give good enough performance. Of course this can and 
should be investigated offline with a given raw data set analyzed with varying 
algorithms.

	- Gerard

p.s. Details on the frontend to processor daisy-chain: I expect this to be able 
to run at 80MHz, possibly 100MHz or more. There are 18 bits, but let's say 2 are 
just used as flags to manage the transfer, so this is >160 MB/s. There is one of 
these per main/mezzanine set of 36 channels, i.e. total data rate into 
"processor" FPGA is limited to 320 MB/s (or 400 MB/s if you can get 100 MHz, etc.)

p.s.2. For filter design I have used "meteor" which is available at 
http://www.cs.princeton.edu/~ken/meteor.html .

On 8/6/2013 11:25 AM, Cody Dickover wrote:
>
> Hi Gerard,
>
...>
> 1. There was some question at the tracking meeting about up-sampling on a constant basis vs. some small region and the headroom involved for that. I assume we are in the green on that, but am not familiar with the code nor the implementation. Do you have some detail on that?