Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!bloom-beacon!apple!oliveb!amiga!cbmvax!jesup
From: jesup@cbmvax.UUCP (Randell Jesup)
Newsgroups: comp.sys.amiga
Subject: Re: 2090A card and hi-res screens
Message-ID: <6138@cbmvax.UUCP>
Date: 3 Mar 89 19:39:20 GMT
References: <8903022014.AA25100@queen.csri.toronto.edu>
Reply-To: jesup@cbmvax.UUCP (Randell Jesup)
Distribution: na
Organization: Commodore Technology, West Chester, PA
Lines: 19

In article <8903022014.AA25100@queen.csri.toronto.edu> drz@csri.toronto.edu (Jerry Zarycky) writes:
>I am having trouble loading 640x400 4 bitplane screens from my harddrive.
...
>I realize that the card's software uses DMA to do the I/O and that it is
>largely being soaked up by this sort of screen, but why does it slow down
>to such an extreme crawl?

	Because it has a 64-byte FIFO for buffering, and with 640x{200|400} 4
bitplanes there are no free cycles for DMA while the beam is on screen, and
it overflows often.

>I take it that this is a shortcoming with the software in the EPROMS.
>So I ask Commodore "Will this ever be fixed?"

	Well, I'd say the problem is with the hardware :-), but there are
software workarounds we plan to implement when next we upgrade the driver.

-- 
Randell Jesup, Commodore Engineering {uunet|rutgers|allegra}!cbmvax!jesup