How to get clock latency value before CTS?

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hgby2209

Joined: 07 Mar 2003
Posts: 122

03 Nov 2004 2:36 How to get clock latency value before CTS?

Currently, I pass my netlist & constraint to APR engineer to run a rough CTS then get clock slew report, and base on the skew report to set clock latency.

But if I don't want to run the rough CTS , how can I get the clock latency value?

carrie

Joined: 05 Sep 2003
Posts: 32

03 Nov 2004 6:40 Re: How to get clock latency value before CTS?

During pre-layout stage, such as logic synthesis and pre-layout STA, you should treat clock signals as ideal nets, and set estimated values for clock skew and clock latency. The values can be general for the technology you choose, or your design requirement. It's bettter that the values are close to the actual after layout.

hgby2209

Joined: 07 Mar 2003
Posts: 122

03 Nov 2004 16:11 Re: How to get clock latency value before CTS?

Thanks!! carrie, I know what you talk about.
But I want to know how to estimated the value for clock latency?

heartfree

Joined: 31 Oct 2004
Posts: 95
Helped: 1

04 Nov 2004 10:51 How to get clock latency value before CTS?

It's not easy to estimate clock latency before CTS. But you check your clock spec for CTS, from that,you can get some information about final CT, such as:
how many level in CT, what kind of cell in CT, max fanout of cell in CT, then
you can roughly estimate clock delay .

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farmerwang

Joined: 29 May 2002
Posts: 60
Helped: 1

06 Nov 2004 3:08 Re: How to get clock latency value before CTS?

There is no way. It's very design/tool/experience dependant. But normally, clock latency is not a big issue, it only affects your IO path in the chip. And IOs are normally fliped before they coming into or going out of the chip.

hgby2209

Joined: 07 Mar 2003
Posts: 122

06 Nov 2004 16:44 Re: How to get clock latency value before CTS?

I need to give APR engineer the latency value as CTS spec.
if I can't estimate the value, how can APR engineer do the CTS?

floatgrass

Joined: 07 May 2002
Posts: 68
Helped: 1

04 Jan 2005 15:28 Re: How to get clock latency value before CTS?

apr designer may insert clock tree automatically, eg, socencounter. according to the design . of course ,you can estimate. I think you let tools automactical.