Howard Price wrote: > Thanks for this info. Surprisingly, I'm still using my *real > SAM* to program on right now!!!!
My real one is fairly inconvenient to use - I need access to the main TV, and I have to put it back in it's box so my wife doesn't complain about it being untidy! :-D > I generally took 78000 TStates per frame to be the norm for > Mode 4 - this roughly equates to Aley's quote of 30-32% memory > contention speed loss. Some test cases to give best/worst cases: NOPs are fairly efficient because only the opcode fetch requires a RAM access, and the timing is a round 4 t-states. During the 6144 on-screen blocks there is an additional 4 t-state delay per instruction for the memory access, giving 8 t-states. You can do 23808 NOPs in a mode 3/4 frame, which would take 95232 t-states in theory. With 119808 t-states per frame, that gives 79.5% of full speed. OUT (254),A is less efficient, as there are opcode and operand fetches that may be contended, as well as an ASIC port access for yet more delay. You can do just 6528 of those per mode 3/4 frame, which would take a be 71808 t-states in theory (assuming an unrounded 11 t-states from the documented Z80 timings). That gives a running speed of just 60% of full speed! Real programs will tend to average between the two, and probably more towards the efficient side (not many instructions will access ASIC ports)... Si
