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From: Crown (all posts)
Date: 1999-09-27
Subject: Re: ECM+MCM black out mode...

Hi,

I haven't checked but I think it won't stop DMA. DMA starting and stopping event is tied to specific raster lines. I guess you want to make the screen a little bit smaller thus gaining some extra lines where no DMA is happening.
You can do this by bringing the end of the screen window up some lines.
An example:
You wait for the raster line 0x0090 by polling $ff1d or by using a raster interrupt,
and then write 0x00a0 into $ff1d/$ff1c. This will cause the end of the screen window to be 16 lines higher, so you will get 16 lines more where there is no DMA.
After this you will wait for the line 0x00f0, and write 0x00e0 into
$ff1d/$ff1c.
This step is needed to put the line counter back where it should be, so no further events which are tied to the raster counter are moved from their place
(like vsync etc...)
And of course do this in a loop...

Tibor Biczo

----- Original Message -----
From: Mike Dailly <REMOVE_ME_mike@scotch.demon.co.uk>
To: <plus4@c64.rulez.org>
Sent: Monday, September 27, 1999 00:31 AM Subject: ECM+MCM black out mode...

> Hiya all...
>
> I have a question...
>
> Blanking out the screen disables character DMA and speeds the Plus/4
> up.. great! But it doesn't work on a scanline basis...
>
> So, what about ECM + MCM black out mode?
> (for those that don't know... setting these bits causes the screen to
> go black)
>
> Does this stop DMA? Does it speed up the plus/4 at all?
>
> This would be handy to know... I could use a little bit more speed on
> my current project, and this kinda thing works great (done it on a few
> consoles.)
>
> If not... any other ideas?
>
> Cheers,
> Mike
>
>
> ^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^`'~*-,._.,-*~'`^
> Mike Dailly
> mike@scotch.demon.co.uk
> http://www.scotch.demon.co.uk
> (Please remove the <REMOVE_ME> from my e-mail address when replying)
> --this message went through the plus4@c64.rulez.org emailing list---
>