Re: [hatari-devel] PSG_WaitState() inaccuracy

[Christian Zietz <czietz@xxxxxxx>]

Christian Zietz schrieb:

> But this is not a difference in *memory* timing but an inaccurate
> emulation of the *PSG* access timing. It just becomes more easily
> observable if code is run from outside of ST RAM.

To underpin this point consider the attached program that can be run
from ST-RAM in a stock ST (or STE) and will still show the inaccuracy:
Hatari 680 ticks, real hardware 554 ticks.

The sequence "CLR.L Dx; MOVE.B Dx,(A1)" where A1 is 0xFFFF8800 takes 16
cycles on real hardware: 6 for the CLR.L, 10 for the MOVE: 8 + 1
waitstate during PSG access + 1 waitstate for re-synchronization of the
next (prefetch) access to ST-RAM.

Regards
Christian
--
Christian Zietz  -  CHZ-Soft  -  czietz@xxxxxxx
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Attachment: psgtime3.zip
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