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| From: Crown (all posts)
Date: 1998-09-07
Subject: Re: FF30, timers, FF11
|
Hi,
>I found at first that some programs (eg. Elite by Pigmy) access $FF30-
>$FF3D part of memory. As far as I know there is nothing to access.
>What should I emulate there?
$ff20-$ff3d is a RAM/ROM area just like $ff40-$ffff. What's here depends on the banking and the RAM/ROM switches.
>An other problem: I was not able to code proper emulation of timers.
>Usually cause no problems at all, except timer-based protectors. (I
>wrote at least 3 of them in '92... ;)
>So please tell me: after the write to the $ff00 and $ff01, when will
>the timer start? (Right after, some delay, or before the end of the
>opcode?)
The next cycle after the write it will be already decremented by one,
if I remember right, this applies in slow mode. Do not forget that it decrements every two double-clock cycle. I didn't checked it yet if it is aliased at all, and if yes whether it's aliased against odd or even cycles. Will do the test, and let you know the result.
>Problems with digi: Crown wrote once, there are intermediate levels
>between the 9 level of FF11, and can be accessed in several values
>written in. Can anybody send me a(n almost) correct table of levels
>for each value between $80-$ff?
Look back, in the archives, I think I gave a pseudo-code to calc it correctly.
Tibor Biczo / Crown of GOTU ICQ : 15989510
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