What is Reset Cloning and Why is it Needed ?

Reset Cloning:

Resets are high fanout signals. Reset timing closure (reset recovery and removal timing) becomes challenging with high clock frequencies and requires cloning to limit the fanout. So, sometimes physical design team recommends to limit the reset fanout to not more than #n flops for all high frequency clock domains (Ex : 900MHz, 1GHz, 2GHz). For low clock frequencies (Ex : < 200MHz) it is not a must requirement.

Here are some thoughts and implementation examples:









Note: This causes one extra clock cycle for reset release.