Path: utzoo!utgpu!watmath!att!dptg!rutgers!sun-barr!newstop!sun!kilowatt!raz
From: raz%kilowatt@Sun.COM (Steve -Raz- Berry)
Newsgroups: comp.sys.amiga.tech
Subject: Re: DMA or polling (was Re: GVP controller)
Message-ID: <120542@sun.Eng.Sun.COM>
Date: 10 Aug 89 02:03:51 GMT
References: <8908092130.AA23369@jade.berkeley.edu>
Sender: news@sun.Eng.Sun.COM
Reply-To: raz@sun.UUCP (Steve -Raz- Berry)
Organization: Sun Microsystems, Mountain View
Lines: 54

In article <8908092130.AA23369@jade.berkeley.edu> 451061@UOTTAWA.BITNET (Valentin Pepelea) writes:
>Steve -Raz- Berry  writes in <120232@sun.Eng.Sun.COM>
>
>> In article <8908072207.AA14796@jade.berkeley.edu> 451061@UOTTAWA.BITNET
>>  (Valentin Pepelea) writes:
>>
> [old argument deleted]
>
>Clearly you don't understand, or perhaps I did not explain well. The bottleneck
>here is the speed at which the hard disk turns, and therefore the rate at which
>data is available to the DMA channel. That is why DMAing directly from the hard
>disk to internal memory is a loosing proposition. GVP provides a cache into
>which it reads from the disk while leaving the Amiga's 680x0 alone. Only then
>does it transfer the data from the cache into internal memory at full speed,
>without having to wait for the mechanical limitations of the hard disk.

The Hardframe also provides a FIFO (call it a cache if you like) on
board. I would think that if a DMA controller operated slower that the
bus it's connected to, then that would fall under the catagory of
brain-dead.

>Perhaps it should then DMA from its cache into internal memory, but that is
>another question. Even if it did that, it still would get lower diskperf's than
>the A2090 or HardFrame. The improvement would be rather limited, and the cost
>would be higher. The GVP controller is expensive enough as it is.

How do you justify that? DMA means running at bus speeds, full tilt, all
out gangbusters etc. You are using every cycle to transfer data, up to
the limit imposed by the device driver. The only increased cost that I see
is in the engineering time put into it. The Hardframe goes for $299, I
don't see that as astronomical, especially when you can probably get
$50 off of that price mail order. {Computer Mart has it for $257}

>> Sorry, this is one EE type that
>> just won't believe it. The Amiga is a DMA machine, that is part of
>> what gives it it's amazing speed for graphics and sound.

>Obviously some EE types are better than others. Good luck on your '030
>accelerator design.

I'll take it. I *know* it's going to be a bitch.

>> (this is part of my effort to insure a "kinder and gentler" netdome)

>Perhaps you meant "thunder.net.dome". Two men enter, one flamed leaves.
>Valentin

I told you via email, I mean no malice. If you refuse to accept that
that's up to you.

---
Steve -Raz- Berry     Disclaimer: It wasn't me! I was volatilizing my esters.
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