What is the advantage of hierarchy over flatten mode in backend design ?

[owen_li]

Hi guys.

Can you tell me the advantage of hierarchy in backed design ?
I find hierarchy brings many trouble.
For example, when we edit the netlist in PrimeTime, we shoud ensure the objects
in the same hierarchy. So it is hard to modify the netlist manually.
So why not using flatten mode in backend design ?

Thanks!

 

[lostinxlation]

Re: Hierarchy or Flatten

When you do ECO, you'd appreciate the hierarchical boundaries.

 

[aravind]

Re: Hierarchy or Flatten

Hi,
Hierarchy flow can be used , when ur design clk is asynchr. with the hiearchy . Also u should have confident CTS can be performed.. I assume hiearchy flow mean partitioning flow.. correct...

Best of luck.

Aravind

 

[owen_li]

Re: Hierarchy or Flatten

Hi aravind

Thanks for your reply.
In my question, the hierarchy doesn't mean partiton. I know partition (hierarchy) flow facilitate the reuse ability. But as we know, every in the block design which has been partitioned from top level. There are still many hierarchys in this block.
What I mentioned is this hierarchy brings much trouble when we do backend design. Why not flatten the block ? Is there any advantage or another reason that we leave the block with hierarchy ?

Thanks !

 

[GI]

Re: Hierarchy or Flatten

Hi Owen,

As lostinxlation said, one of the reasons may be ease of ECO application with hierarchical flows. Most of the backend tools normally removes hierarchies in order to do better timing optimizations. Some of them has hierarchical flows.

Personally, in my previous projects I faced up with ECOs done by front end team in a hierarchical way (which was the normal methodology at front end). They did a lot of operation on hierarchical ports which do not "physically" exist anymore in backend tool due to flattening. Some of the ECOs were easy to manage, however some of them were real pain! In these cases, you need to synchronize with the ECO owner and should request him not to do operations at hierarchical ports. Of course this was related to an older version of Magma Blastfusion (2005), and this kind of behavior may not exist in other tools.

Therefore "the ease of ECO implementation" may be one of the reasons you're looking for.

Best regards,
Gokhan
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[entropy]

Re: Hierarchy or Flatten

Hi guys.

Can you tell me the advantage of hierarchy in backed design ?
I find hierarchy brings many trouble.
For example, when we edit the netlist in PrimeTime, we shoud ensure the objects
in the same hierarchy. So it is hard to modify the netlist manually.
So why not using flatten mode in backend design ?

Thanks!

Of coz you should use flatten mode whenever possible but guess how to cope with 5M instance design??? After a single command, you'll have to wait for 10 hours...