Retention registers characterization

Status
Not open for further replies.
N

nitin kala

Junior Member level 1
Joined
Apr 17, 2010
Messages
15
Helped
1
Reputation
2
Reaction score
1
Trophy points
1,283
Location
Hyderabad
Visit site
Activity points
1,347
Hi all,

1. What is the meaning of setup time for SAVE pin ( asynch pin ) of a retention register wrt CP pin.
2. If SAVE pin is active high, then why only fall_constraint is considered for setup_rising ( CP rising edge ) in .LIB file ?

Regards & Thanks,
Nitin Kala
nitin.kalaji@gmail.com
 

It is basically means the time taken for the data to be stored in the always on latch. But in industry we try to avoid the timing on "save" pin. These are low activity and kind of DC signal for the chip level. The timing constraints can avoided for the save pin and be taken at the chip level.
 

Thanks artmalik.

1. Save is an asynchronous pin. So why to measure setup time for an asynch pin ? generally we measure recovery and removal ( although like setup and hold only ). So why the name setup here ?
2. In .lib file, only setup_rising ( CP pin rising ) for fall_constraint ( SAVE pin falling ) is mentioned. It means when SAVE pin deasserts. So how this can cause problem to me? If it is about SAVE pin rising around somewhere CP ( which i doubt as it is asynch ), probably then i can check for setup violations. But how to check when it is falling.
3. So what do you recommend ? should i characterize this or not as per industry requirements and standards ?

Regards,
Nitin
 

I use the retention flops with ANY timing on the save pin in chips that we tapeout. It is not required, but i think the characterization guys who generated the .libs have been over enthusiastic the data. If you constraint the design properly, when you are trying to save the data, then all the clocks should be at zero state. You should keep enough time for this to happen. So you can use the .lib number ,use the worst case timing information add some padding. then use this number as the difference in the time before all clocks are shut off to the point you activate the save pin
 

Status
Not open for further replies.

Similar threads

Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…