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Xref: sserve comp.os.386bsd.development:1718 comp.sys.ibm.pc.hardware.chips:1909 comp.periphs:4945 Path: sserve!newshost.anu.edu.au!munnari.oz.au!constellation!news.uoknor.edu!ns1.nodak.edu!netnews.nwnet.net!news.clark.edu!spool.mu.edu!agate!howland.reston.ans.net!vixen.cso.uiuc.edu!sdd.hp.com!col.hp.com!csn!hellgate.utah.edu!cc.usu.edu!ivie From: ivie@cc.usu.edu Newsgroups: comp.os.386bsd.development,comp.sys.ibm.pc.hardware.chips,comp.periphs Subject: Re: The DMA problem again! Message-ID: <1994Jan24.103126.8590@cc.usu.edu> Date: 24 Jan 94 10:31:26 MDT References: <jmonroyCJxHBH.2x0@netcom.com> <1994Jan22.120513.8484@cc.usu.edu> <jmonroyCK4tFo.3Jx@netcom.com> Organization: Utah State University Lines: 36 In article <jmonroyCK4tFo.3Jx@netcom.com>, jmonroy@netcom.com (Jesus Monroy Jr) writes: > ivie@cc.usu.edu wrote: > : In other words, DMA channel 0 is not involved in refresh. > : > From the facts you have previously stated, > no logic can be derived to state DMA channel 0 is > not involved in the refresh. Sorry. Point being that if DMA controller channel 0 were used for refresh, either the DMA request or the grant would go somewhere involved with refresh; since it only goes to the connectors and the DMA page registers, it can't be used to do refresh. > This makes two of us... I don't think I've ever > stated that the FDC can hang the "refresh". > I am saying the inverse (or is it the converse, anyhow). > I beleive the DMA RAM refresh signal is interfering > with the FDC transfer. Again, sorry. Lost track of what the argument was. From sheet 21 of the schematics, it looks like you're right, Jesus. A DMA request is captured and synchronized to the DMA clock by the flops on top of the sheet. However, the request then goes to the two flops in the middle of the sheet; these flops decide who to give the grant to. When the refresh request is made, the top flop becomes set. This does two things: it grants the DMA request to the refresh controller and it clears the grant to the DMA controller. There's nothing in there to stop the grant from being ripped away from the DMA controller if a refresh request comes along in the middle of a DMA transaction. -- ----------------+------------------------------------------------------ Roger Ivie | Don't think of it as a 'new' computer, think of it as ivie@cc.usu.edu | 'obsolete-ready'