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Xref: sserve comp.os.386bsd.development:1710 comp.unix.bsd:13314 Path: sserve!newshost.anu.edu.au!munnari.oz.au!bunyip.cc.uq.oz.au!harbinger.cc.monash.edu.au!msuinfo!agate!dog.ee.lbl.gov!hellgate.utah.edu!cc.usu.edu!ivie From: ivie@cc.usu.edu Newsgroups: comp.os.386bsd.development,comp.unix.bsd Subject: Re: Late comments on the DMA problem. Message-ID: <1994Jan21.095505.8375@cc.usu.edu> Date: 21 Jan 94 09:55:05 MDT References: <jmonroyCJy610.HB7@netcom.com> Followup-To: comp.os.386bsd.development,comp.unix.bsd Organization: Utah State University Lines: 21 In article <jmonroyCJy610.HB7@netcom.com>, jmonroy@netcom.com (Jesus Monroy Jr) writes: >>> For example, it is not possible to implment "scatter/gather" with the FDC by >>> ^^^ > ||| > I think he meant to say that "it is possible", because I know > it is. Evidence is the the FDC (flexible drive controller) > has a command for read-a-track. Yes, but "scatter/gather" has nothing to do with the FDC's read-a-track command. Scatter/Gather involves organizing the DMA such that DMA happens from virtually contiguous addresses when pages are crossed; in other words, at a page boundary you have to be able to switch to some page other than the next physical page. Since you can't get an interrupt to tell you that the DMA controller has finished doing a page, you can't reload the DMA addresses when the end of a page is reached. -- ----------------+------------------------------------------------------ Roger Ivie | Don't think of it as a 'new' computer, think of it as ivie@cc.usu.edu | 'obsolete-ready'