Timing Violations workaround strategy

Hi Jens,

1. yes at once becaus the fitter is using timing constraints.

Well ... this is probably a critical point that I fail to understand: after all timing relations e.g. clock/clock, clock/interface signal are influenced by routing.

Here I mean that fitter can be quite "smart" and will route all tracks so that NONE adjusting with PLL clock shifting or multicycle is necessary.

But this can be known AFTER fitting is run at least one time. Or I missed something ?

2. it's the virtual clock for the i/o timing analysis (see quartus ii handbook, qii5v3 2015.05.04. p. 7-14 or the timequest user guide from ryan scoville, http://www.alterawiki.com/wiki/timequest_user_guide)

In these two sources virtual clock is created because it's external (i.e. generated OUTSIDE FPGA) whereas on my board both "SDRAM clock" and "SDRAM controller clock" are generated INSIDE FPGA.

Is it also your case ?

3. no, i use the shift calculated according the embedded peripherals ip user guide

Ok, but I meant something other. It seems that in the "Embedded Peripherals IP User Guide" this shift is used to setup phase shift between 2 clocks, generated by PLL and it's the ONLY remedy against timing violations ... because they don't mention multicyling. My question was about eventual possibility to use ONLY phase shift for timing violation workaround (without any multicycling). Did you try this ?

do you drive the internal sdram_controller with the same clock as the external sdram device? the external clocks should be shifted.

No, they are driven by 2 clocks. These 2 clocks are PLL-generated and shifted one relative to other according to "Embedded Peripherals IP User Guide" procedure.

in your screenshot the launch clock should be the external shifted clock and the latch clock is the internal clock.

That is strange because clk_ext_sdram is actually u0...divclk.

the multicycle -setup constraint is used to tell timequest what is the right latch edge.

I considered that timequest is quite "smart" and capable to deduct it itself.

After all, multicycle option isn't mandatory, how TimeQuest manage this if there is no multicycling.

Thanks once more.