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[DC] Determine parameter in set_input_delay?

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davyzhu

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Hi all,

When use set_input_delay/set_output_delay, how to determine the -max/-min parameter? Is it calculated by hand , calculated by tools, or give out by some standard specification?

Code: 
set_input_delay -max 498  -clock EXTSCL [find port ddc_sda_i]
set_input_delay -min 0    -clock EXTSCL [find port ddc_sda_i]

set_output_delay -max 498 -clock CLK1MHZ [find port ddc_sda_o]
set_output_delay -min 0   -clock CLK1MHZ [find port ddc_sda_o]

Best regards,
Davy
 

General concept is to use time budgeting. 40% of clock period is used as input and output delays
 

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    davyzhu

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Hi Megastar007,

Thanks, so the delay is calculated by hand, is it right?

Best regards,
Davy
 

Hi ,

This should be as a part of specification .
In general if you are doing synthesis of module you do 40% of clk . But if you constrain the same at SOC you need to go through data sheet and get the same .


Thanks & Regards
yln
 

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    davyzhu

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I think we should estimate the outside environment for the chip to give the input delay value. I am right?
 

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    davyzhu

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If u synthesize modules which is nothing without outer environment, that use 40% clock period; if else, should refer datasheet of outer chip.
 

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    davyzhu

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Hi davyzhu,

It is totally dependent on the environment where your design is going to sit.

For example if your input is driven by a block/chip which is fast enough to give the output in 20% time
then your design budget is 80% of clock period.

For a block level or IP design these margins are specified by the architect whereas at chip level this
is driven by a application requirements.:|
 

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    davyzhu

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these come under timing exception !! .....
which specifies delays on various ports
 

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    davyzhu

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