Path: utzoo!utgpu!watmath!att!pacbell!ames!haven!grebyn!ckp From: ckp@grebyn.com (Checkpoint Technologies) Newsgroups: comp.sys.amiga Subject: Re: GVP controller Message-ID: <12254@grebyn.com> Date: 9 Aug 89 03:28:32 GMT References: <8908072207.AA14796@jade.berkeley.edu> Reply-To: ckp@grebyn.UUCP (Checkpoint Technologies) Organization: Grebyn Corp., Vienna, VA, USA Lines: 27 In article <8908072207.AA14796@jade.berkeley.edu> 451061@UOTTAWA.BITNET (Valentin Pepelea) writes: > >Unfortunately >this means that there are two transfers occurring, a slow DMA from hard disk >to the cache, and a fast CPU transfer from the cache to internal memory. Other >controllers such as the A2090 and HardFrame DMA directly from the harddrive >into internal memory, thus tying up you CPU much longer. > >So if you multitask a lot, you'll want the GVP controller, otherwise the other >controllers are for you. Facts are sound - but the conclusion is backwards! On such as a HardFrame or A2090, the controller moves data *directly* into the data's final resting place, using one bus cycle per 16 bit word. With the GVP, the data moves into the controllers on-board RAM using no bus cycles, but then the CPU must move the data to it's final location, using *6* bus cycles (four for the 68K instructions moving the data, and two for the data, one coming from the controller RAM and one going to the task buffer) for each word. This means that a DMA controller is *less* taxing of the CPU during a transfer than a non-DMA controller like the GVP. -- First comes the logo: C H E C K P O I N T T E C H N O L O G I E S / / \\ / / Then, the disclaimer: All expressed opinions are, indeed, opinions. \ / o Now for the witty part: I'm pink, therefore, I'm spam! \/