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| author | Duncan Smith | 2010-06-12 11:07:10 -0700 |
|---|---|---|
| committer | Duncan Smith | 2010-06-12 11:07:10 -0700 |
| commit | 9540f9351745b0a5386c014031d14c160f0ed6cd (patch) | |
| tree | 04b1658b2dce54465d9930024e6cae982ac35ce8 /README.markdown | |
| parent | 49f38304e22252b1eb07aba3333eba23cbc5dae8 (diff) | |
| parent | cf1021b481694b00e1b18bbc9dab67ab8c6c7553 (diff) | |
Merge branch 'debrouxl'
Diffstat (limited to 'README.markdown')
| -rw-r--r-- | README.markdown | 12 |
1 files changed, 6 insertions, 6 deletions
diff --git a/README.markdown b/README.markdown index 38a9f52..827339c 100644 --- a/README.markdown +++ b/README.markdown @@ -19,20 +19,20 @@ The most difficult challenge in writing a 68k-hosted emulator targetting the z80 is making it _fast_. TI-83+ calculators have a clock rate in the neighborhood of 12MHz, as do TI-89s. z80 instructions take from 4 to 17 cycles to execute. I can dispatch an -instruction with a fixed 30 cycle overhead: +instruction with a fixed 42 cycle overhead: emu_fetch: eor.w d0,d0 ; 4 cycles move.b (a4)+,d0 ; 8 cycles - rol.w #5,d0 ; 4 cycles adjust to actual alignment + rol.w #5,d0 ;16 cycles adjust to actual alignment jmp 0(a3,d0) ;14 cycles - ;; overhead: 30 cycles + ;; overhead: 42 cycles From there, an instruction will take anywhere from 0 to, well, lots of -additional cycles. Generally, however, it will take under 50, for 80 +additional cycles. Generally, however, it will take under 50, for 92 total. In the worst reasonable case, a 4 cycle instruction emlulated -in 80 cycles, that's a 20:1 ratio. In the best possible case, a -17-cycle instruction emulated in 30 cycles, is more nearly a 1:2 +in 92 cycles, that's a 23:1 ratio. In the best possible case, a +17-cycle instruction emulated in 42 cycles, is more nearly a 1:2 ratio. I am not aiming for exactly correct relative timing of instructions, |
