Ricardo Bittencourt wrote:
> > I think the VDP statusregister is being reset upon readout
> > in the MSX interrupt routine itself...
>
> Not really. The bios handler read the vdp status register
> AFTER calling 0FD9Ah. If you read the status register before the bios
I thought the ISR read it _before_ #FD9A and that AF has to be
preserved because of that... (since the BIOS uses it after the hook to
test if it's a VDP interrupt).
> does it, the handler is aborted (which means 0FD9Fh never gets called
> and the other processing is not done also, such as keyboard polling).
> I believe this is the fastest possible way to grab the irq handler
> inside the basic environment.
Well the fastest way is using IM 2.
The easiest way is this one, yes.
> > Anyways, relocating the hook to #FD9F is a much, much nicer
> solution I
> > think.
>
> The only real advantage of this method would be the stop-drive,
> but that doesn't matter because I call 0FD9Fh 120 times at the
> startup of my program :)
Why not just 256 times (ld b,0)???
Maybe it keeps turning longer than 2 seconds on some MSX types...
~Grauw
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