>> Hi John, >> >> Do you have the coefficients in slices rather than BRAMs? That might >> be contributing to the high address fanout. > > Yes, the "use distributed memory cells for coeffs" is checked. I'll try > changing it. It takes forever to build, but I'll start one and leave it > go.
This made a significant difference, so much so that I don't trust it. It took only a couple of hours to build, and used *many* fewer slices... I'll keep you posted. (btw, the "use distributed memory cells" is the default.) > > (note to the list: I sent Henry the mdl file, instead of sending it to the > list as it's 4.5 MB. Let me know if you want a look at it.) > > John > > >> Thanks, >> Henry >> >> John Ford wrote: >>>> Hi John, >>>> I've definitely run into the same issue, but haven't had a chance to >>>> tackle it yet. It could be a pain, but I would try to hack the design >>>> to change the PFB coefficients by one LSB or something in one location >>>> so they can't be optimized together. It might also help to try and >>>> change whether the coefficient ROMs are implemented in BRAM or >>>> distributed memory. If it comes down to it, you may have to add a >>>> delay to one section of the PFB so that the coefficients are off by >>>> one time step (the optimizer doesn't seem to be smart enough to figure >>>> that one out), and then add delays elsewhere to get things back in >>>> step later. >>>> It seems like there has to be a way to get that optimization turned >>>> off, but I haven't figured it out. >>> >>> Thanks. These are some good suggestions. The error is in the counter >>> that addresses the coefficients, so maybe I can do as Jason suggests >>> and >>> add in some delay between the counter and the rest of the system inside >>> the PFB block. Maybe I can trick it into thinking the counters are >>> different, somehow... >>> >>> John >>> >>> >>> >>>> Glenn >>>> >>>> On Thu, Nov 6, 2008 at 10:07 AM, John Ford <jf...@nrao.edu> wrote: >>>>>> Create more coefficient generators and sprinkle them around inside >>>>>> the >>>>>> PFB? >>>>>> >>>>>> Sorry, I don't have Simulink with me, so can't offer more concrete >>>>>> advice. But if the problem is with the fanout, why not create >>>>>> seperate >>>>>> sources with smaller fanouts? >>>>> There are separate coefficient generators for every path in the >>>>> library >>>>> block, but they seem to get optimized out during the build. That's >>>>> the >>>>> trick, I guess, that I don't know how to get around... >>>>> >>>>> Thanks >>>>> >>>>> John >>>>> >>>>>> Jason >>>>>> >>>>>> >>>>>> On 06 Nov 2008, at 15:46, John Ford wrote: >>>>>> >>>>>>> Does anyone have any suggestions for fixing this error? It seems >>>>>>> due >>>>>>> entirely to the large fanout (450!) in the coefficient generator. >>>>>>> >>>>>>> We're stuck on this for building our 4K channel 800 MHz pulsar >>>>>>> machine. >>>>>>> It is introducing errors into the spectrum. >>>>>>> >>>>>>> John >>>>>>> >>>>>>> >>>>>>>> Hi all. Here's a timing error that appears when building a large >>>>>>>> (2^^3 >>>>>>>> parallel paths, 2^^13 points, 4 taps 7 bit coefficients, 7 bit >>>>>>>> input, 14 >>>>>>>> bit output) PFB. The timing wizard's suggestions are below. Note >>>>>>>> that >>>>>>>> the coeff. generator counter seems to be used for all coeff >>>>>>>> generator >>>>>>>> counters in the entire PFB's complement of coeff generators. >>>>>>>> >>>>>>>> How can I tell the toolset not to optimize out all the other >>>>>>>> counters, or >>>>>>>> alternatively, how can I introduce a delay to fix this problem? >>>>>>>> I've >>>>>>>> attached the twx file, but from the timing wizard: >>>>>>>> >>>>>>>> This path has a net >>>>>>>> "b2_gdsp_u1_8k_800_a_nb_xsg_core_config/ >>>>>>>> b2_gdsp_u1_8k_800_a_nb_xsg_core_config/ >>>>>>>> top/pfb_fir_real_4k_ch/pol1_in1_first_tap/pfb_coeff_gen/counter_q(4)" >>>>>>>> with a high fanout of 450. >>>>>>>> >>>>>>>> High fanout suggestions. >>>>>>>> >>>>>>>> -Duplicate the net source and direct the synthesis tools not to >>>>>>>> remove >>>>>>>> duplicate logic. >>>>>>>> >>>>>>>> -Use a specific net fanout control on the problem net if allowed >>>>>>>> by >>>>>>>> the >>>>>>>> synthesis tool. >>>>>>>> >>>>>>>> Click Next button if this suggestion does not help. >>>>>>>> >>>>>>>> Thanks for any help! >>>>>>>> >>>>>>>> John >>>>>>>> >>>>>>>> >>>>>>>> >>>>>>> >>>>>>> >>>>> >>>>> >>>>> >>> >>> >>> >>> >> > >
