Re: ROM Dump of Amiga Keyboard controller

From: Jim Brain <>
Date: Sat, 19 Jul 2014 00:19:51 -0500
Message-ID: <>
On 7/19/2014 12:15 AM, Gerrit Heitsch wrote:
> I'm curious how that is "optimized"  :-)  Doesn't it also need an INY in
>> there?  With that added, it takes more cycles and more codespace...
> No, it takes less cycles since Y is loaded with $#10 once at the 
> beginning to the program before entering any loop. Then it's used as a 
> constant to compare against while your code always loads the contents 
> of $08 into the accu and then compares it against #$10. So instead of 
> LDA/CMP (5 cycles) you only have the CPY (3 cycles) inside the loop.
Ah, I misread it as an immediate load.  Not a detail person, as I said.  
Yes, that is better and satisfies my original goal of not using a 
synthetic counter.

> Not that it really makes any real difference, but if there is a spare 
> register I can use, I like to use it.
Fair enough.


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Received on 2014-07-19 06:00:33

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