Hello I am now well into a design, and in testing it seems to work, the timing reports are good, and so on. But I strongly suspect te immense power of ignorance is helping me. The design is large, a Zynq 7045 will be congested, by the time it is all put together. My question, where is it safe, and where is it not safe, to use combinatorial logic, in a piece of user-designed IP? Many thanks to anyone who replies, Geoff