Reset Recovery and Removal Time

[vipulsinha]

reset recovery time

Hi All

In the Async Reset based designs the Reset covery and reset removal time plays an important role. We go for the concept even like Async reset assertion and Synchronous removal.

1. My question is when the Async reset is asserted it doesnot looks for the clock signal. Is there any chance of flops going to metastable state when Asyc reset is asserted?

2. The removal time we talk about is the time offset between Clock Deassertion and Reset Assertion. How to take care of it ?

3. If we talk about the reset Synchronizer at the assertion time also then wht is the use of Async reset as it will be synchronized to the clock signal so why not then use synchronous Reset?

Regards

Vips

 

[mmarco76]

recovery removal time

1- The register will not go in metastable state while it's been resetted, moreover it could be that you don't know what state is the register (1,X or 0) exactly each instant of time but you'll be sure that you'll know it after 1clk cycle.

2- The only way I know is to synchronize the async reset with the negate of register's clock

3- I suppose you prefer to use asyncronous reset instead of synchronous one just because in a big design you usually have to reset things that are clocked by different clk domain (and so you use an async reset that locally can be synchronized with the negate local clock register in order to prevent problem in removal time)

Hope to help, but I think that a lot of others can help more

 

[ksahil]

hi...

i have one doubt that even if we synchronize the reset, then wont there be any problem when that synchronized reset is going in design and reseting a flop in which clock is skewed w.r.t clock used in reset synchronizer....

thanks