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Path: euryale.cc.adfa.oz.au!newshost.anu.edu.au!harbinger.cc.monash.edu.au!news.rmit.EDU.AU!news.unimelb.EDU.AU!munnari.OZ.AU!news.ecn.uoknor.edu!news.cis.okstate.edu!newsfeed.ksu.ksu.edu!news.physics.uiowa.edu!math.ohio-state.edu!usc!howland.reston.ans.net!newsfeed.internetmci.com!in2.uu.net!en.com!multiverse!ragnarok.oar.net!malgudi.oar.net!hyperion.wright.edu!news.wright.edu!usenet From: John Meyers <jmeyers@nostromo.wright.edu> Newsgroups: comp.unix.bsd.netbsd.misc Subject: Re: DMA beyond end of ISA Date: Sat, 27 Apr 1996 23:32:10 -0400 Organization: Wright State University Lines: 23 Message-ID: <3182E6BA.33C3@nostromo.wright.edu> References: <4lqvhh$aa@kayless.thalgah.org> NNTP-Posting-Host: dup152035.wright.edu Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Mailer: Mozilla 2.0 (Win95; I) Robert Leon Felix wrote: > > OK an easy one for you this time, 'DMA beyond end of ISA', I've > heard of this before but know not of the fix. This is a classic problem with DMA based ISA controllers such as the 1542. In summary, to the best of my knowledge (which may not be 100% correct), the problem is due to the fact that DMA addressing is limitted to 16MB on a 16-bit ISA bus. There is a work-around commonly refered to as 'bouncing-buffers' which I believe involves transferring data from above the 16MB boundary to the lower 16MB prior to performing a disk operation (can someone provide more detailed information?). Anyway, I don't believe that the code has been implemented yet in the latest stable version of NetBSD. However, both FreeBSD and Linux have implemented the 'bouncing-buffer' solution in their kernels. So until it's implemented under NetBSD, you may want to only use 16MB of memory or alternatively use FreeBSD. John Meyers Computing Services Wright State University