Asynchronous and synchronous reset are mixed!

[dewdrop]

Now i am reading some ip's rtl code, i found that both asynchronous and synchronous reset are used in this module. Is the good coding style?
What should I take care about in designing these asynchronous and synchronous mixed module?

 

[lostinxlation]

Depends. If using async reset is fine to make it functional, why not. And some block may not have running clock upon the start-up and may need async reset.
If you want to make it all synchronous, put sync flops before the async reset port.

 

[dewdrop]

Depends. If using async reset is fine to make it functional, why not. And some block may not have running clock upon the start-up and may need async reset.
If you want to make it all synchronous, put sync flops before the async reset port.

Thanks a lot!
Can you explain futher why we should put the sync flops before the async reset port?

 

[lostinxlation]

Because you can make sure all the flop meet reset recovery and removal time and can avoid a potential metastability issue.

 

[sakshi gupta]

That means you are ensuring that reset is asserted asynchronously & deasserted synchronouslly & there are no reset removal & recovery issues .

 

[vs21]

No, not a good practice. Make sure what your top level architecture says, and keep a uniformity throught the design.

 

[krishanu007]

Depends. If using async reset is fine to make it functional, why not. And some block may not have running clock upon the start-up and may need async reset.
If you want to make it all synchronous, put sync flops before the async reset port.

this is very good explanation...u need to synchronize the reset signal with the destination clock domain...by a normal synchronizer block....