Date   : Mon, 23 Jan 1995 14:16:20 +0000 (GMT)
From   : Mark Cooke <ee2015@...>
Subject: Re: Scrolling Swapping

Dave,

> I time everything by processor opcodes as you suggest your does, therefore
it should
> just about work - but my screen timing is slightly off - I think - I'm
not taking
>  account of the extra half scanline per field due to interlace - and also
my interrupt
> entry latency is probably also duff.

Well, I draw the screen a scan line at a time, one every n ticks (I'm not
at my PC so can't tell you exactly what I'm using) counting from the
vertical sync.  There was a bit of discussion on one of the newsgroups
sometime last year about how long each scan line should take given the PAL
spec.  I'll see if I can find it again.

Also, as a point of information, IRQ and NMI have a 7 cycle delay before
executing the next opcode.  This is from the opcode information by various
people (it's on my web pages - see below).  This info documents the
illegal opcode functions and details exactly how each instruction works.

Mark

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