Thread: What is multi-cycle path?

What is a multi-cycle path, and how can I determine wither a path is a multi-cycle path.

if u have a big combinational logic in ur design which will never run at ur required frequency...
u have 2 options

1)Add pipeline stage(s) to divide the logic into single-cycle paths
2. Ease off the single-cycle requirement: allow more clock cycles using set_multicycle_path command.

DC will allow more clock cycles for path delay when checking for setup/hold violations...when u specify a path as multicycle path


rgds

Usually DC/PT check path timing in one cycle.
If you have a path in your design ,which cannot finished operation in one cycle, you can tell DC/PT this path is a multi cycle path.
At same time, you should guarantee that output of this path can be correctly flopped by next stage.
It's designer's responsibility.

Ye, it's up to the designer whether the path is multi-cycle path according the the synthesis ability about the max frequency may be achieved.
one import thing is the hold timing for the multi-cycle path, it should be the setup_cycle-1

One path that need multi cycle to complete

how I can decide the time checked for the setup/hold time? for example the circuit must be 3 clocks. what's the setup time? and what's the hold time?

how I can decide the time checked for the setup/hold time?
This depends on the flop that is used and the library vendor datasheet should give you the setup and hold times

the multi-clock path is defined in design specification. if you don't kown which is multi-clock path in design process, usually use PT to check path timing in one cycle.

how I can decide the time checked for the setup/hold time? for example the circuit must be 3 clocks. what's the setup time? and what's the hold time?

For PT, your setup time requirements for the multicycle path is 3 clock cycle, if you constraint the path to:
set_multicycle_path 3 -setup -from <> -to <>
PT by default will check your hold time at 3-1 clock cycle.
However, you can specify the hold time check to be checkat clock 0 as below:
set_multicycle_path 2 -hold -from <> -to <>