Routing

by kamalnadh

Routing:-
               Before the routing stage the connection between the macros,standard cells,clock,i/o port are logical connections.In this stage we connect all the cells physically with the metal straps.The routing done in different steps.

Steps in routing:-

   1.Global routing.

   2.Track assignment.

   3.Detailed routing.

   4.Search and repair.

Global routing:- It is done to provide instructions to detailed routing about where to route every net.It  provides the logical connections to all cells.First the design is divided into small boxes which are called Gcell. Each Gcell have the horizontal and vertical routing resources.It's aim is to reduce the total interconnect length and minimize the critical path delay.By using global routing we can analyse congestion.

Track assignment:- It assigns each net to a specific track and lays down the actual metal tracks.

Detailed routing:-   Before detailed routing the connections are logical.In this stage all the cells are physically connected.In this we specifies the wire/interconnection in the channels specified by the global routing.Metal layer information of the interconnections are also specified here.The violations that are created in track assignment are fixed in this stage.It does't route entire chip at a time.By dividing the chip into small boxes(G cells) it will do routing. DRC's are fixed in detailed routing.

Search and repair:- It fixes the remaining DRC violations  through multiple loops using progressive layer Sbox sizes.

Goals of routing:-

• Minimize the total wire length.
• Minimizing the congestion hotspots.
• Reducing the cross-talk.
• Minimizing no.of via's.
• Meeting the timing DRC's.