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From: aduncan@rhea.trl.oz (Allan Duncan)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Amiga Custom Chips
Message-ID: <3396@trlluna.trl.oz>
Date: 18 Apr 91 00:43:12 GMT
References: <9104172234.AA04604@sun2.emr.ca>
Sender: news@trlluna.trl.oz
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 In article <20298@cbmvax.commodore.com> daveh@cbmvax.commodore.com (Dave Haynie) writes:

>Specific to the Amiga, there were several problems.  First of all, the video
>chips are directly tied to video.  If you speed up the bus cycle, you speed
>up the video shift rate, unless you go to a multiple of it.  The current Agnus
>runs a 280ns cycle.  To double that, and go to 140ns, you would need 60ns
>DRAM, which are only now becoming available in large quantities, and are still
>quite expensive (though, if they're on schedule, they'll get cheap in the next
>year or so).  Any somewhat faster bus speedup and you lose NTSC or VGA scan
>and pixel rates.  While it's conceivable that you could divorce the scan
>rate from the bus rate, that's a MAJOR architectural change, far more complex
>than building new chips that speed up in other ways (32 bit bus is the way
>the microprocessors gained their modern speed, more than clock rate speedups).

I would have thought that _full_ 32 bit chips would also allow
equivalent 140ns operation while keeping Dram speed down - isn't the
3000 variant halfway to this?


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