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I'm quite clear (at least in my mind): The multi-cycle path simply tells TimeQuest that Tsu for Latch_FF is not met at T1 but at T2 it is. The output of Latch_FF is irrelevant at all times except at T2. Therefore, the source signal is launched by Launch_FF.Q at T0, captured by Latch_FF.D at T1 (Latch_FF.Q possible metastable but this is don't-care since Latch_FF.Q is only used at T2) and finally captured by Latch_FF.D at T2.
Downstream logic will ignore the output from Latch_FF.Q until t == T2.
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This doesn't look good..
This is what it looks like to me:
T0: Launch_FF latches a new value
T1: Latch_FF latches a bad value, as the previous transition from Launch_FF hasn't completely propagated yet
T2: Latch_FF latches a good value as the previous transition finally had time to propagate; downstream_FF latches a bad value, from the bad value Launch_FF had before.
T3: Downstream_FF finally latches a good value.
Or making it short.
An exception like "set_multycycle_path -from [launch_FF] -to [latch_FF]" concerns the path between launch_FF.Q and latch_FF.D.
If you're making considerations for stuff downstream of latch_FF or upstream launch_FF, and coming to an exception that like, then you're getting it wrong.
Honored Contributor
