Re: [stella] Qb: v0.03

Subject: Re: [stella] Qb: v0.03
From: Chris Wilkson <ecwilkso@xxxxxxx>
Date: Thu, 15 Feb 2001 02:23:37 -0500
In message <007a01c09714$4de112b0$0100a8c0@screamer>, "Andrew Davie" writes:

>double-height/single-height routine, but I ran into a situation where I
>really DID need to waste just one cycle, and couldn't do it.
>Something like this...
>    sty loop                ; 3
>   bcs SingleLine    ; 2(3)
>   >> need to waste ONLY ONE cycle here
>        lda (S0),y ;5
>        sta GRP0                ; 3 = 15
>...etc's been ages since I thought about software. (yay!)

LDA (S0),Y adds the contents of Y to the contents of S0 to get an effective
address (EA), and stores the contents of the EA in A, right?  Hrm...

Don't suppose you could reorganize, so that you branch to the lda instruction?
Not sure of the context here.

Can you align the code so the the LDA instruction crosses a page boundary?
That'll give you an extra cycle.

Question:  Do the GRP timings depend on when the instruction starts, or
when it finishes?  If it's when it finishes, you can use the TIA mirror
at GRP0+$100.

That's all I can think of right now....


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