A Crystal analysis of the ALU was performed to determine the longest path through the circuit. The .cryvec file, the result file, and a view of the crystal path paint on the alufin cell are available below.
Crystal's estimate of the longest path through the ALU is from the asc control input of the least significant bit to the most significant bit of the accumulator. This makes sense, since we would expect the longest path through the ALU to be from the lowest order to the highest order bit. The time required for the signal to propagate is 264.09 ns. If we were to use Crystal to estimate a maximum clock frequency, we would double the longest path to be conservative, giving a minimum period of approximately 550 ns. This would result in a maximum clock frequency of 1.80 MHz. Because this value is so small and because Crystal analysis is very conservative and often unrealistic, we used Spice to obtain a more accurate estimate of the longest path. The results of the Spice analysis can be found on the Performance Analysis page.