68k timing

[meynaf]

Originally Posted by Toni Wilen

List few cache fitting routines with cycle counts included and I'll check if there is something obviously wrong. (no MULs or DIVs!)

Ok. First attempt (winuae 3.1.0, no jit, approximate a1200) :

.loop
 moveq #1,d0      ; 2
 lsl.l d2,d0      ; 6 (8)
 dbf d7,.loop     ; 6 (14)

Timing with the lsl is 1.33 that of the same code without it. Should be 1.75.

I can't guess the intended cpu frequency so i can't really count clocks...

Originally Posted by Toni Wilen

It won't work. It would make many demos with MULs or DIVs to run too slow and skip frames. (worst cases are not that common, no static cycle count is common enough) They need to be accurate. Unfortunately 68020+ MUL and DIV are "too fast" to make any easy guesses of used algorithm. (vs 68000 which also had microcode listing helping)

If the worst case can't work, then remove a few clocks out of it. Perhaps something close to the best case would suffice.
For MUL the "simple" cases are usually made without it, so remove 2 clocks from the max and it should be ok.
Same with DIV, this instruction rarely appears in time critical code anyway ('xcept in my prime number factorization program and in my 5:3 downsampling routine ).

But perhaps a few stats made from various value could reveal, if not the algorithm, at least its true speed ?

[PiCiJi]

For emulating the 68020 it’s hard to calculate the right amount of internal cycles between bus cycles, because of the non hardcoded design. The correct placement of bus cycles matters so that other bus masters access the right values at the right time on shared memory.

By the way, the docu says something about dynamic bus sizing in combination with address alignment affects the number of bus cycles for byte, word or long word transfers. It's clear from a internal point of view.
The question is what port size is externally set for amiga system (always 32 bit) ?
Depends this from memory type, like chipmem, cia ...?
Is there a difference between amiga 1200 and 68020 turbo carded A500 system?

[meynaf]

Originally Posted by PiCiJi

Is there a difference between amiga 1200 and 68020 turbo carded A500 system?

Yes there is a difference. A1200 accesses chipmem with 32-bit, where turbo A500 only does 16-bit.
The chipset is 16-bit and has same timing as chipmem.
CIA are even slower than chipmem.

[PiCiJi]

thanks for information folks

[PiCiJi]

M68000 user manual ninth edition:

The transition from supervisor to user mode can be
accomplished by any of four instructions: return from exception
(RTE) (MC68010 only), move to status register (MOVE to SR),
AND immediate to status register (ANDI to SR), and exclusive
OR immediate to status register (EORI to SR).

68000 RTE instruction can't switch back to user mode? some documentation error ?

[meynaf]

If the manual says that, then yes it contains an error. The cpu wouldn't work at all if RTE couldn't go back to user mode !

[amilo3438]

Originally Posted by meynaf

Btw. I would like to have more accurate 020/030 timings under winuae for suitable code optimizations, as for now the "cycle exact" timing is about as wrong as in max speed with jit active. It doesn't need to be 100% cycle exact, just better than what we have now.

If compared with a real A1200 in SysInfo, the 68EC020 "cycle exact" timing in the latest WinUAE3400 does not look so bad !

And I hope there still exist chance for some more improvement.

[Toni Wilen]

Sysinfo speed test is simple and stupid, real world is much much much ... much more complex.

[amilo3438]

Originally Posted by Toni Wilen

Sysinfo speed test is simple and stupid, real world is much much much ... much more complex.

Definitely agree, so it can be used only for "quick & dirty" comparison test. (and for a such test it does not need to be 100% exact)

But in a case of A500 and 68000 it seems to be pretty accurate ! (as shown in attached picture)


EDIT:
However, playing with the SysInfo can give some "useful" results !
For more see the post #111 on "Problematic AGA demos" topic, or: --> http://eab.abime.net/showpost.php?p=...&postcount=111