6.5 Hint 5 - Use XOR Synthesis

When a design includes XOR logic, enabling the XOR synthesis feature can significantly reduce the number of required product terms. This feature uses the hardware XOR gate available in the ATF15XX/ATF1500A macrocell to implement XOR logic efficiently. By default, XOR synthesis is enabled by the fitter. If this feature is disabled, XOR logic is implemented as a sum‑of‑products expression, which may consume a large number of product terms and potentially prevent the design from fitting into the ATF15XX/ATF1500 device. To assist the fitter, ensure that XOR synthesis is enabled, review the intermediate equations feeding XOR logic, and define these equations as nodes where appropriate.