Three approaches in flip-flop default value ECO
HEIDI ZHENG
Manager at NanDigits, Functional Netlist ECO, Functional Safety Fault Verification
Flip-flop default value ECO is also called settable/resettable flop swapping or register file ECO. There are three approaches to achieve flop default value ECO.
The first approach involves the dedicated implementation of ECO flops. Some standard cell libraries include specialized ECO flops that are specifically designed for efficient switching between settable and resettable flops. Settable flops have the same pins as resettable flops, with only minor differences in a few metal layers. In functional ECO, the affected flops simply need to be renamed to match the desired mapping flops. Additionally, there are several changes in the metal layers during the back-end place and route work. This method provides the advantage of a quick turnaround time. However, a drawback of this approach is that ECO flops tend to be larger in size compared to regular flops.
The second approach involves directly swapping a regular settable flop with a regular resettable flop, or vice versa. This approach provides a straightforward solution for achieving flop default value ECO. However, it introduces challenges in metal-only ECO, as the corresponding flop may not be easily accessible in close proximity.
The third method involves inverting the input and output phase of the flop while keeping the flop itself unchanged. This approach relies on the availability of invert cells, which are typically abundant in metal ECO. Finding nearby invert cells to insert into the input and output paths of the flops is relatively easier with this method. However, it does require special settings in the Logic Equivalence Check (LEC) tools used for verification purposes.
GOF ECO encompasses all of these approaches for flop default value ECO. For more information, please visit https://nandigits.com/index.php .