Article View: comp.sys.amiga.tech
Article #2596Re: DMA vs Non-DMA
From: Colin Plumb
Date: Thu, 07 Dec 1989 21:36
Date: Thu, 07 Dec 1989 21:36
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1374 bytes
In article <1989Dec6.151618.3097@sjsumcs.sjsu.edu> 33014-18@sjsumcs.SJSU.EDU (Eduardo Horvath) writes: > Is there a bug with the Amiga DMA scheme that causes data to be lost > under some obcure conditions, or is that somebody mis-reading > a 2090 review again? Sigh... There is no bug in the Amiga's DMA scheme. There is a bug in the 2090 that causes it to drop bytes when there is severe memory contention (such as DMA into chip memory with 4-bitplane high-res screens), but it detects this condition and retries. The 2090 bug does not cause lost data, only enormous numbers of retries. The details are that the 2090 does not do anything with the "buffer full" indicator on its FIFO... it naively assumes the buffer can be flushed to memory faster than the disk reads. So it keeps asking the disk for data even though it can't accept it. This causes problems. -- -Colin
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Path: arc1-ca.pugleaf.net!utzoo!attcan!utgpu!watserv1!watdragon!rose!ccplumb From: ccplumb@rose.waterloo.edu (Colin Plumb) Newsgroups: comp.sys.amiga.tech Subject: Re: DMA vs Non-DMA Message-ID: <19078@watdragon.waterloo.edu> Date: 7 Dec 89 21:36:38 GMT References: <1989Dec1.152959.5833@dvinci.usask.ca> <1989Dec6.151618.3097@sjsumcs.sjsu.edu> Sender: daemon@watdragon.waterloo.edu Reply-To: ccplumb@rose.waterloo.edu (Colin Plumb) Organization: U. of Waterloo, Ontario Lines: 19