Re: [stella] Strange glitches in homebrewed games on the 2600 jr.

Subject: Re: [stella] Strange glitches in homebrewed games on the 2600 jr.
From: Thomas Jentzsch <tjentzsch@xxxxxx>
Date: Fri, 28 Feb 2003 15:22:26 +0100
Dennis wrote:
> I first thought that the problem was that all three games set the timer during vertical sync. Crazy Valet also sets the timer during vertical sync and it doesn't have any reported problems (I asked someone to test it on their jr).
> The other noticable thing is Vault Assault and Skeleton set HMPx during vertical sync but 'Qb' doesn't.

I have wondered about that too. I remember I had some problems with Thrust or Jammed when doing HMOVE during VSYNC. I *am* writing to HMM1/BL and RESM1/BL with no reported problems. 

Maybe the timer access is the problem. 

Did you check if VSYNC is always enabled long enough? Something like

  lda #2
  sta VSYNC
  sta WSYNC
  sta WSYNC
  sta WSYNC
  lda #0
  sta VSYNC

doesn't work 100%, because the first line may be hit much to late.


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