what is routing? types of routing? when can we say.. it s good routing?

[shrikantec]

what is routing? types of routing? when can we say.. it s good routing?

 

[anishjoseph007]

in ASIC design, once we have done with the rtl coding and the functional verification; the next step is the synthesis. so in the design we wil have a lot of modules and interconnections. in synthesis we are making these in to a real hardware. here we have to actually decide where to place each modules on the chip. once the placement is done we have to connect the modules using interconnects. this process is collectively called placement and routing.

routing can be called good routing once it holds the timing and clock skew requirements

 

[Ow@i$]

Interconnections b/w your modules i.e. drawing physical copper traces to connect your modules is called routing, good routing depends on your application circuit for RF routing standard would be different and for ASIC high speed digital signals it would be different in general avoid sharp 90 degree turns in traces, for differential signal do differential routing try to keep analog and digital section separate and etc.

Cheers!!

 

[alam4vlsi]

Hi,

Routing:
Routing refers to the process of physically connecting the instances in your design.
There are four steps of routing operations:

1. Global routing
2. Track assignment
3. Detail routing
4. Search and repair

Global Route assigns nets to specific metal layers and global routing cells. Global route tries to avoid congested global cells while minimizing detours. Global route also avoids pre-routed P/G, placement blockages and routing blockages.
Track Assignment (TA) assigns each net to a specific track and actual metal traces are laid down by it. It tries to make long, straight traces to avoid the number of vias. DRC is not followed in TA stage. TA operates on the entire design at once.
Detail Routing tries to fix all DRC violations after track assignment using a fixed size small area known as “SBox”. Detail route traverses the whole design box by box until entire routing pass is complete.
Search and Repair fixes remaining DRC violations through multiple iterative loops using progressively larger SBox sizes
For more details Visit http://www.vlsi-basics.com/2013/07/physical-design-flow.html

Thanks,
Alam

 

[ro9ty]

I would just like to add to alam4vlsi.
Understand this : The chip has various metal layers. In our consideration let us take 6metal layers. Let us assume M1,M3,M5 are used for horizontal and M2,M4,M6 for vertical. Each of them have several tracks, i.e virtual lines on which the copper interconnects could flow once the chip is fabricated. Let us assume that for a chip of die (3000X3000 um) we have 15000 tracks for each metal layer (0.1 width and 0.1 pitch).
What happens during routing is this :-
1> In global routing the aim of the tool is to just assign the nets (which are declared in verilog/netlist as wire) to the metal layers with minimum deviation and avoiding long straight routes etc.. It has a very basic objective-Make sure that all the layers can accommodate the routing given the congestion and area might sometimes not be sufficient to accomodate all wires. In such cases floorplan would have to be changed.
2> If global route is pass and H and V congestion on the metal layers is not huge then we understand that there will not be many DRC violations and we go ahead with the track asignment. Track assignment is assigning tracks out of the 15000 tracks on metal layer to some net. That ways the resources are allocated. Please do not think that one track is for one net only. It is for one net only in one co-ordinate, it could be for some other net in some other co-ordinate. Track does not mean the physical wire, it is just a guide.
3> Detail routing is like differentiation. It will break t whole die into small pieces called SBox and then for each SBox it will complete the routing and minimize he DRC ( spacing, notch etc...)

You can call a route a good route by looking at these 3 things basically:-
1> DRC violations
2> Timing after SPEF extraction (especially SI for long nets)
3> Congestion for each metal layer

Ro9ty

 

[pdude]

What is the difference between Z-route and normal route ?

 

[Ow@i$]

What is the difference between Z-route and normal route ?

Never heard any such thing as Z-route, where do you get it from.... probably it is talking about differential route and normal route!!!

 

[ro9ty]

I don't know exactly what you are referring to there are two things.
Z-route is usually one way of routing also called double bend routing where a global route is made using double bends.
Another thing is a feature that was introduced in some PnR tools called Z-router which use an advanced engine for routing with a better algorithm which has proven to result in lesser congestion and better timing correlation.

Ro9ty