[stella] Re: robbie.a65

Subject: [stella] Re: robbie.a65
From: mor@xxxxxxx (Greg Troutman)
Date: Mon, 14 Oct 1996 10:04:55 -0700
>Top:    ; Start a new screen
>        LDA     #$05      
>        STA     Tim64T	; set timer for $05*$40 = $140 (320d) clocks

There are 228 color clocks per scan line.  The RIOT timer intervals once
every 3 color clocks.  Thus a scan line should take 76 ticks of the interval
timer (228/3).  There are 30 scan lines in overscan.  Thus you need to count
2,280 (30 * 76) on the timer.  Using the 64interval timer, you get 35 ticks.
Not 5.  Or something like that. 

>        LDA     #$05	; put $05 in A
>        STA     Tim64T  ; start vblank timer

Similar math here for 37 scan lines of vertical blank.

Your programs work fine on the emulators, except you lose the bottom half or
so of the screen (it's just blank) because you're not waiting long enough
before doing VSYNC or while you VBLANK. Increasing these waits should fix it
no problem.

gt (mental as anything)

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