Quite right about the terminology, thanks. FIFO is just the pointer I wanted to hear. I tried the example on p433 of the Camel, and it told me I "will visit the Dung Pits of Glive soon", which is the best news I've heard about this all day. Many thanks, I'm on the road. BTW, the test harness, which I've previously considered, is very nice but requires change to the drivers.