High-Level Model of c2670
Statistics: 233 inputs; 140 outputs; 1193 gates
Function: 12-bit ALU and controller
This benchmark consists of an ALU with a comparator, an equality checker, and several parity trees. The comparator has two 12-bit inputs X and Y, and computes Y>X using a carry-lookahead adder (CLA) that performs the addition !X+Y. It can be programmed to do a 4, 6, 8 or 12-bit comparison of its inputs. An interesting feature of the comparator is that it uses two identical CLAs that have identical inputs, a redundancy technique commonly used in fault-tolerant systems. The CLAs have a fairly standard structure with 3, 4 and 5-bit blocks. The carry output signal of each CLA gives the result of (Y>X). The output labeled OutYgreaterX_Equal (line number 231) is constant 1 if the outputs of the two CLAs are identical, as would normally be the case. If, however, the CLAs produced different results, the OutYgreaterX_Equal output would be logic 0, implying an error in the circuit. This would happen, for example, if there were manufacturing defects in one of the CLAs.
Module M7 (EqualZ_W) performs an equality check on two 17-bit buses. The ParityChecker module (M8) contains five 10-input parity trees, whose outputs are all ANDed. This module seems to perform a sanity check on the input buses of c2670. There are also several small pieces of logic which are mostly random.Inputs/Outputs vs. Netlist Numbers
Models:
- I. Original ISCAS gate-level netlist
- II. Verilog hierarchical netlist (functionally equivalent to I)
- III. Verilog flat netlist (flat version of II; functionally equivalent to I, but with minor structural differences)
* Netlist numbers for input buses A[9:0] and B[9:0]:
* Input buses Y1[5:0], Y2[5:0], Y3[3:0]:
* Inputs X[11:0] and Y[11:0] of CompareXY (M4):
* Inputs W[16:0] and Z[16:0] of Bitwise Comparator (M7):
* Q[9:0], R[9:0], S[9:0] (inputs to ParityChecker M8) are three 10-bit buses multiplexed out of Y1, Y2, Y3 and ParTreeIns:
* Netlist numbers for the remaining inputs:
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2096, 2100, 2678, 2454, 2451, 2446, 2443, 2438, 2435, 2430, 2427, 2474 |
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* Netlist numbers for outputs:
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164, 160, 162, 171, 168, 166, 299, 301, 286, 303, 288, 305, 290 |
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158, 188, 176, 259, 234, 217, 223, 156, 173, 369, 367, 411, 384, 337, 409, 391, 350, 335 |