casper-scm Distributing code for V5 optimized PFB

[Suraj Gowda]

Hi all,

I've "developed" a PFB FIR real optimized for V5, making the (now  
usual) modification of directly instantiating dsp48s to use the same  
multipliers and adders.  The problem is that this particular  
optimization requires eliminating the "tap" block in the PFB and doing  
all the multiplications in the same block.  Which makes it  
incompatible with the drawing architecture of the previous block

I was able to compile an 8-input 1024 channel PFB (w/FFT) at ~286 MHz  
with no floorplanning, so my guess is that it will be an part of the  
GBT spectrometer and other high speed spectrometer efforts.  Are there  
any serious objections to me adding a "pfb_fir_real_roach" block? The  
V2 version can be incorporated eventually.

Sidenote: Can someone tell me how the amount of downshift after the  
adder tree was derived? It seems excessive in the case I simulated.

Thanks,
-Suraj