What is congestion in routing and how to reduce it?

[vreddy]

congestion

wat is congestion in routing & how to reduce it?

congetsion ----disturbance bet the nets......
horizontal congetsion ----0.5% good for metal 3 layers
vertical congetsion-------1% good for metal 6 layers

correct me if am wrong??

also , wat happen if we use lower metal layer placing horizontal & higher metal layer placing vertically in the design??

thanx in advance

 

[vlsi_deepa]

Re: congestion

Hi,
congetsion ----disturbance bet the nets......
horizontal congetsion ----0.5% good for metal 3 layers
vertical congetsion-------1% good for metal 6 layers

You told congestion limit values for metal3 and metal6.
Can u plz tel me,wats the congestion limiit for M1,M2,M4,M5,M7 and M8? and

How can you determine these values(0.5% for m3 and 1% for m6) ? Any formulas are there?

Thanks & Regards,
Deepa

 

[roy_ece]

Re: congestion

congestion Analysis is stage in design you usually do it at Trial Route ,where
you estimate the Demand for routing and check it with the supply routing possible because of Design rule(fab )limits.
Generally in any layer process m1,m3,m5... will be horizontal layers.
m2,m4,m6... will be vertical layers.
Any place and route tool estimates both horizontal ,vertical track congestion
congestion =demand for routing(number of metal wires of same layer)/available number of wires for routing.

Generally fab fix the limit of % congestion of 0.5 for 3 layer metal
1.0 for 5 layer metal.
This limit specifies if congestion is under the specified value design is routable.

 

[p_shinde]

Re: congestion

when demand (for routing resources) is more than supply congestion occurs...

 

[vreddy]

Re: congestion

Thanks Shinde,

But how to reduce the congestion in the design even if we r selecting the highest metal layer still congestion is seen.......is there any other method to reduce the congestion......??

Thanks in advance

 

[rjainv]

congestion

try different floorplans, move the placement blockages away from the congestion area.

 

[p_shinde]

Re: congestion

only higher metal layers....is not the solution...as discussed in this topic....blockages can be changed.......floorplan can be redesigned........or something else....but for that one should know the cause of congestion......

 

[rjainv]

congestion

also if you have a option of resynthesis, try disabling area recovery... that can also help by not choosing complex cells, but limit to 2/3 input cells only...

 

[shiv_emf]

congestion

may be density screens will help in getting some more resources!!!

blockages will also do .....but 100% is nt required

 

[shiv_emf]

congestion

can v do congestion driven placement????

 

[gangadharn]

Re: congestion

Yes, we can do congestion driven placement. In both Magma and Soc Encouter.