Method of simplifying a circuit for equivalence checking
View Patent ↗A method of simplifying a logic circuit for enabling cycle-by-cycle equivalence checking is provided. To accomplish this, first, a logic circuit is identified to be a variable delay circuit or a fixed delay circuit. If the logic circuit is a variable delay circuit, it is converted to a fixed delay circuit by using additional circuitry to obtain a fixed delay circuit. If the fixed delay circuit is a logic circuit that performs multiple cycle computations, it is converted to a logic circuit that performs the same computation in a single cycle. Circuit acceleration includes concatenating multiple copies of the fixed delay circuit. After performing circuit acceleration on all sub-circuits in the fixed delay circuit, a combined accelerated circuit is obtained. Thereafter, redundant flip-flops are identified and removed from the combined accelerated circuit and the combined accelerated circuit is optimized.
1. A method of simplifying a logic circuit, the simplification being performed for achieving cycle-by-cycle equivalence checking between the logic circuit and a second logic circuit, the logic circuit being a sequential logic circuit or a combinational logic circuit, the method comprising the steps of:
a. identifying whether the logic circuit is a variable delay circuit;
b. if the logic circuit is a variable delay circuit, then converting the variable delay behavior to fixed delay behavior by adding an extra circuitry in the logic circuit;
c. accelerating the logic circuit to produce an accelerated circuit for each output of the logic circuit, the acceleration being a circuit transform achieved by mapping the multi-cycle behavior of the logic circuit to one cycle behavior;
d. combining all the accelerated circuits to get a combined accelerated circuit;
e. identifying constant valued flip-flops in the combined accelerated circuit, the constant valued flip-flops being those flip-flops that do not change their values in any state of the combined accelerated circuit; and
f. removing constant valued flip-flops from the combined accelerated circuit, the remaining circuit being termed as a simplified accelerated circuit.
2. The method as recited in claim 1 further comprising the step of obtaining a simplified second accelerated circuit from the second logic circuit by performing steps a to f recited in claim 1 .
3. The method as recited in claim 2 further comprising the step of performing equivalence checking on the simplified accelerated circuit and the simplified second accelerated circuit.
4. The method as recited in claim 1 wherein the step of identifying constant valued flip-flops comprises the step of determining the values of flip-flops in the combined accelerated circuit during each clock cycle.
5. The method as recited in claim 1 wherein the constant valued flip-flops are identified using the process of iterative relaxation.
6. The method as recited in claim 5 wherein the process of iterative relaxation comprises the steps of:
a. initializing a RESET list that includes the flip-flops with known reset values in the accelerated logic circuit;
b. starting all flip-flops in the accelerated logic circuit;
c. computing the next state equations of these flip-flops;
d. identifying a subset of flip-flops in the RESET list, which do not reach reset values;
e. if the subset of flip-flops is not empty, then removing the flip-flops belonging to the subset from the RESET list; and
f. repeating steps b-e until the subset of flip-flops becomes empty.
7. The method as recited in claim 1 wherein the step of removing constant valued flip-flops comprises the step of performing constant propagation in the combined accelerated circuit.
8. The method as recited in claim 1 further comprises the step of performing dead code elimination in the combined accelerated circuit.
9. A computer program product for use with a computer, the computer program product comprising a computer usable medium having a computer readable program code embodied therein for simplifying a logic circuit, the simplification being performed for achieving cycle-by-cycle equivalence checking between the logic circuit and a second logic circuit, the computer program product performing the steps of:
a. identifying whether the logic circuit is a variable delay circuit;
b. if the logic circuit is a variable delay circuit, then converting the variable delay behavior to fixed delay behavior by adding an extra circuitry in the logic circuit;
c. accelerating the logic circuit to produce an accelerated circuit for each output of the logic circuit, the acceleration being a circuit transform achieved by mapping the multi-cycle behavior of the logic circuit to one cycle behavior;
d. combining all the accelerated circuits to get a combined accelerated circuit;
e. identifying constant valued flip-flops in the combined accelerated circuit, the constant valued flip-flops being those flip-flops that do not change their values in any state of the combined accelerated circuit; and
f. removing constant valued flip-flops from the combined accelerated circuit, the remaining circuit being termed as a simplified accelerated circuit.