Forum Discussion

cjak's avatar
cjak
Icon for Occasional Contributor rankOccasional Contributor
3 months ago
Solved

Constraining an unclocked output?

Hi, I am trying to achieve timing closure, but have trouble constraining outputs that is not referenced to an external clock. Do I have to define a false path for each output?
Timing
  • FvM's avatar
    FvM
    3 months ago

    Hi,

    to declare all IO as asynchronous

    set_false_path -from [all_inputs]

    set_false_path -to [all_outputs]

cjak's avatar
cjak
Icon for Occasional Contributor rankOccasional Contributor
3 months ago

Thanks, but it is a bit unclear to me how I would define the false path:

set_false_path -from [get_pins A*] -to [get_pins B*]

...when -from and -to is the same signal/net/pin?

  • KennyT_altera's avatar
    KennyT_altera
    Icon for Super Contributor rankSuper Contributor
    2 months ago
    • If a port (e.g., reset_in) is truly asynchronous and handled by a synchronizer, you cut the path from the port to the first synchronized flip-flop: set_false_path -from [get_ports reset_in]