Congestion reduction techniques

Congestion Reduction Techniques

This post will give the idea of what is congestion and what are the reasons for congestion how to resolve the congestion problem.  

Congestion  : if the number of available routing tracks is less than the number of required routing tracks

Before going to reduction techniques will first know the reasons for it.

Reasons

• High standard cell density in small areas
•  High standard cells near macro edges
•  High pin density areas (M2 M3 routing congestion) due to AOI, OAI, flops
• Rectilinear block shape
•  At last the bad floorplan or height or width of the block.

Reduction techniques:

First analyze the root cause for congestion before setting the high effort  options to reduce congestion . ( if we enable such options run time will be high and timing may be degraded)

• After seeing the congestion maps check the congested area having high standard cell density. If you see such case than apply the partial blockages with less than the density in that particular area.

          Eg: if the congestion regions is let say 80% utilization then apply partial blockage with 60% like

•  If you see the congestion near to the macro area then apply 5-10 microns of soft or hard blockage (better is 5 microns hard and 5 is soft is better). Because high critical timing path cell will be seated in the soft blockage area in the optimization phase.

• If you see the congestion M2 M3 layers apply cell padding to the high number of pin standard cells (Eg. AOI, OAI,Full adders or other 4 i/p gates   )

• Congestion is at rectileanior areas apply the partial blockages