Reduce QoR Variability for Low Reuse Mode - 2020.2 English

In low reuse mode, you can reuse particular cells (for example, a hierarchical cell in the design) or cell types (for example, DSPs or block RAMs). This can be effective when both of the following are true:

• Some design runs are showing that a design can meet timing but many runs do not.
• It is early in the design flow or significant changes are still being made.

Reusing hierarchical cells is effective when placement of a particular cell is influencing the WNS significantly. Reusing DSPs, block RAMs, or both is useful in designs that have a relatively high density of these blocks.

To reuse particular cell or cell types:

• Analyze the reference runs, including checking failing checkpoints to identify the difference between good and bad runs.
  • Identify runs that have a good WNS and low congestion levels.
  • Use floorplanning to define SLR placement.
• After determining the area to target, compare a set of runs using low reuse mode against a baseline set of runs using the default flow to evaluate effectiveness.
  • Use different place_design directives to generate multiple results for comparison.

To reuse only block memory placement, use the following Tcl script:

read_checkpoint -incremental routed.dcp \
-reuse_objects [all_rams] -fix_objects [all_rams]

To reuse only DSP placement, use the following Tcl script:

read_checkpoint -incremental routed.dcp \
-reuse_objects [all_dsps] -fix_objects [all_dsps]

To reuse both Block Memory and DSP placement, use the following Tcl script:

read_checkpoint -incremental routed.dcp \
-reuse_objects [all_rams] -reuse_objects [all_dsps] -fix_objects [current_design]

To reuse hierarchy in a particular hierarchical cell and all hierarchies below the cell, use the following Tcl script:

read_checkpoint -incremental routed.dcp \
-only_reuse [get_cells <cell_name>] -fix_objects [get_cells <cell_name>]