> 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 <[email protected]> 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 >>>>> >>>>> >>>>> >>>> >>>> >>>> >>> >> >> >> >> >
