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
- Use different
place_designdirectives to generate multiple results for comparison.
- Use different
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>]