On 22 Jun 2008, at 15:37, Thomas Harte wrote:
ex de, hl
add hl, hl
add hl, hl
ex de, hl
Takes 48 cycles (on the 6 Mhz bus) if executed in its entirety while
pixels are being drawn, 32 cycles if executed in its entirety while
pixels are not being drawn. The functionally equivalent:
sla e
rl d
sla e
rl d
Takes 64 cycles if executed in its entirety while pixels are being
drawn, 32 cycles if executed in its entirety while pixels are not
being drawn?
Yes. I believe these and all your other statements are correct.
Has anyone drawn up a neat table of all the opcodes with cycle
counts computed as weighted probabilities of their timings if
executed entirely in pixels and if executed entirely outside?
David Zambonini wrote up a description of Sam timings for an article
in "Based on an idea" issue 2 (and I may be able to find a text file
he sent me with an earlier version of that article). He expresses the
timings differently, but the data is basically the same; there are a
few instructions which take less time to execute than they "should"
when the screen is on (working out the statistical benefit of that is
just a little bit of maths). It's a good idea to put these into every
algorithm you can get them...
Andrew
--
--- Andrew Collier ----
---- http://www.intensity.org.uk/ ---
--
