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Jorgeb's avatar
Jorgeb
Icon for New Contributor rankNew Contributor
4 years ago

Small change causes LE count to change from 108 to 2660

Whenever I connect SampleNow, in the Baud generator.v file to the SAMPLENOW port, the LE count goes from 108 to 2660?

If I connect OversamplingTick (from which SampleNow is generated), no problems occur. I've shut off clock mux protection, as the SAMPLENOW port connects to a clock mux in serial_trigger.v.

I can trigger this problem without routing SampleNow to SAMPLENOW, but just making SAMPLENOW a reg, and initializing it to *anything* in the reg line?

If I route SampleNow to SAMPLENOW, ignore the fitting error, and simulate, everything works as advertised (other than it doesn't fit...).

Pretty baffled.

2 Replies

  • Jorgeb's avatar
    Jorgeb
    Icon for New Contributor rankNew Contributor
    4 years ago

    Fixed, in my case. The problem was the line:

    LogBitsize(ClkFrequency/baud) was implying an lpm_divide Megafunction. Changed to (LogBitsize(ClkFrequency) - LogBitsize(baud)), and problem resolved. Completely.

    I say that the problem resolved completely because two lpm_div megafunctions were being implied, the second by a different line, according to Quartus. But they *both* went away with the changes above? This highlights the fact that there doesn't seem to be any documentation at what 'implies' an lpm_div Megafunction (or any other megafunction). Nor is there any dox on how to *not* imply these explicitly in Quartus. In general, this was huge waste of time because Quartus inferred something that wasn't there and made a 32 bit barrel shifter.

    How do I stop Quartus from wasting my time? It would be much useful if Quartus *asked* if that was my intention...

  • SyafieqS's avatar
    SyafieqS
    Icon for Super Contributor rankSuper Contributor
    4 years ago

    Thanks for you feedback and this can be a for Quartus enhancement.