Area-aware Logic Synthesis

[ivlsi]

Here are some quotes:

If you use Physical Synthesis (DC-Topographical or RC-PLE), you should not use WLM at all. In the synthesis tool, you should load FloorPlan before making any RTL synthesis (this way you restrict your design by area).

You have to specify information like die size, placement blockages, macrocell placement etc. to take full advantage of this feature.

So, if WLM is not used and RC-extraction is not ready yet, how does the tool calculate timing over interconnects (nets)?

 

[oratie]

It performs some kind of placement (DC-topo makes not-legalized placement), calculates distance between cells (and wire length) and use TLUplus file for calculating RC values. The main difference between WLM and Topographical is that in WLM mode it use esimated wire length (some average value), in Topo mode it use more or less real wire length based on cell placement.

 

[ivlsi]

Thanks oratie! But, where is the TLUplus file taken from? from floorplaning? But how the floorplaning might be performed without any info from the Logic Synopsys about the cells area. Somehow this circuit should be broken :smile:

 

[oratie]

TLUplus come with foundry tech files (or you may generate them from ITF or GRD tech files).

The floorplan may comes from different sources:
1. You have previous design, so you may use it as reference (scale somehow or manually modify)
2. You did (at first) non-topographical synthesis (with WLM, as example), estimate the cell area, take inot account desired utilization (in order to not have any routing congestion issue in the future) and create floorplan.
3. The full chip layout owner gives floorplan of your block (based on full-chip requirements)

It is iterative process.

 

[ivlsi]

Thank you!