Return to BSD News archive
Path: sserve!newshost.anu.edu.au!munnari.oz.au!network.ucsd.edu!usc!howland.reston.ans.net!xlink.net!fauern!lrz-muenchen.de!colin.muc.de!ars.muc.de!rommel From: rommel@ars.muc.de (Kai Uwe Rommel) Newsgroups: comp.os.386bsd.questions Subject: Re: > 16 MB of RAM (on an ISA box) Distribution: world Message-ID: <741742526rommel.root@ars.muc.de> Sender: root@ars.muc.de Date: Sun, 04 Jul 93 00:35:26 MET References: <1993Jul2.164901.22217@leland.stanford.edu> <2121b9$73v@pdq.coe.montana.edu> <1993Jul3.072649.18439@leland.Stanford.EDU> Organization: Private Lines: 28 In article <1993Jul3.072649.18439@leland.Stanford.EDU> yergeau@leland.Stanford.EDU (Dan Yergeau) writes: >Argh! Much of my confusion came from thinking that the wd driver did >DMA transfers (cuz, if that worked OK, the all DMA transfers should >work OK). I should have looked at the source. The wd driver uses the >cpu to transfer data to/from the controller via outsw/insw. > >It looks like, in addition to SCSI controllers, the floppy disk >drives, QIC-02/36 tape drive, and some ethernet cards use DMA and >should eventually cause ugly problems in a ISA box that has more than >16 MB. The key here seems to be the use of "drq" in the config line >for the device/controller. I'm not sure, but the floppy controller, some ethernet card and QIC driver probably use the mainboard DMA chip (at least the floppy controller uses it, that's clear, I think). Unless the QIC controller or Ethernet card have their own DMA chip on the card. And the DMA chip on the mainboard probably doesn't have the 24-bit address bus restriction. Kai Uwe Rommel -- /* Kai Uwe Rommel Muenchen, Germany * * rommel@ars.muc.de Phone +49 89 723 4101 * * rommel@informatik.tu-muenchen.de Fax +49 89 324 4524 */ DOS ... is still a real mode only non-reentrant interrupt handler, and always will be. -Russell Williams