having read this article I got curious about the effect of ZX8301 on memory access latency. As background for discussion, consider replacing (in a special case where the result is known to fit in a word):
Code: Select all
mulu #10,d0
Code: Select all
move.w d0,d1
asl.w #3,d0
add.w d1,d0
add.w d1,d0
I tried searching the forums and among Nasta's fabulous articles on the inner workings of the QL there are several clues that while the ZX8301 reads video RAM it makes the cpu wait. This seems to be the case on other machines as well. From the article quoted above:
Does anyone know what the total "average" slowdown effect of this mechanism for memory accesses is on the QL?For instance, the Macintosh's 68000 runs at 7.8 MHz, but it can't always operate at this speed because the screen is memory-mapped and "steals" some memory cycles. Thus, the effective speed of the Macintosh is about 6 MHz, but only memory cycles are slowed down -- CPU cycles are unaffected.
Kind regards,
Petri