RE: [stella] Another kernel is rolling

Subject: RE: [stella] Another kernel is rolling
From: "Dennis Debro" <dennis@xxxxxxxxxxxxxxx>
Date: Fri, 8 Apr 2005 06:09:33 -0400
Hi Fred,

> Also, it appears from the schematics that there is nothing that would
> cause
> syncing problems when asserting VBLANK at weird times.  In fact it appears
> that we can call VBLANK any time we want, even in the middle of a
> scanline.

Also remember this syncing problem doesn't occur for the "late" VBLANK write
when the old VSYNC macro is used. Here it is just for reference.
; Original author: Manuel Polik
; Inserts the code required for a proper 3 scannline 
; vertical sync sequence
; Note: Alters the accumulator
; IN:
; OUT: A = 1

                LDA #$02            ; A = VSYNC enable
                STA WSYNC           ; Finish current line
                STA VSYNC           ; Start vertical sync
                STA WSYNC           ; 1st line vertical sync
                STA WSYNC           ; 2nd line vertical sync
                LSR                 ; A = VSYNC disable
                STA WSYNC           ; 3rd line vertical sync
                STA VSYNC           ; Stop vertical sync

Also know that I ran this on a 7800. I have not run this on a VCS so the
results may be different on a VCS. I *think* Aaron said some of is testing
was done on the VCS with the same results.

Take care,

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