grouping instances in SoC encounter

[pavi622]

Hi,

I am working on a design, where i dont want to optimise a group of instances.
How can i go about doing this using SoC encounter

 

[morris_mano]

In your SDC input to encounter, you can add

set_dont_touch [get_cells instance1]
set_dont_touch [get_cells instance2]
set_dont_touch [get_cells instanceX]

This will prevent encounter from optimizing instance1, instance2, instanceX.

Usually, logic optimization is done during synthesis. In RC, 'set_attribute preserve true [find / -instance dut]' will be converted to 'set_dont_touch [get_cells dut]' in sdc.

 

[rca]

What do you mean by optimize?
Not removed the logic
Don't change the driver
Don't changed the logic ???

Dont_touch will avoid to removed the logic but the driver could be changed.

 

[pavi622]

the thing is the design contain some memory, but memory complier is not available for hardening the memory. While optimising the rest of the logic, the memory which is realised as flops are also optimised. Reason is SoC encounter see these flops as just instances/standard cell.
As a result, timing cant be closed at desired frequency & is also leading to very high setup & hold violations.

So how to optimise the rest of the design without touching the memory part.

 

[rca]

you could not, because you surely need the specific memory timing model, that will impact your design.