To ensure DFT logic remains inactive during functional ECO, the DFT_MODE signal is set to zero. However, some nets may be equivalent but not suitable for DFT, which can lead to DFT being broken. For instance, in Figure 1, an ECO must select either the mux_in or mux_out signal to drive a reset pin of a flop. Although the two signals are equivalent, Conformal ECO selects mux_in, which breaks DFT. In contrast, GOF can identify the MUX and chooses mux_out as the correct signal for the reset pin, thus maintaining the integrity of DFT logic.
Figure 1: Pick the right signal to maintain DFT logic
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