cline@sun.soe.clarkson.edu (Marshall Cline) (05/16/89)
Two questions: (1) I recently read in the Minix textbook (Prentice Hall) about a DMA caveat that AST had discovered. It had something to do with wrapping around 64K barriers as I recall. Anyway, I can't find the specifics now that a friend needs them :-( QUESTION: Does anyone know the information to which I am refering? Page#? (2) AST mentioned that there is minimal documentation for using DMA. QUESTION: Does anyone know a pointer to more detailed doc on DMA? Thanks in advance Marshall ________________________________________________________________ Dr. Marshall P. Cline ARPA: cline@sun.soe.clarkson.edu ECE Department UseNet: uunet!sun.soe.clarkson.edu!cline Clarkson University BitNet: BH0W@CLUTX Potsdam, NY 13676 AT&T: (315) 268-6591 -- ________________________________________________________________ Dr. Marshall P. Cline ARPA: cline@sun.soe.clarkson.edu ECE Department UseNet: uunet!sun.soe.clarkson.edu!cline Clarkson University BitNet: BH0W@CLUTX Potsdam, NY 13676 AT&T: (315) 268-6591
EPRF%SNYCENVM.BITNET@cornellc.cit.cornell.edu (Peter Flass) (05/17/89)
On Tue, 16 May 89 15:45:03 GMT Marshall Cline said: >Two questions: > >(1) I recently read in the Minix textbook (Prentice Hall) about a DMA >caveat that AST had discovered. It had something to do with wrapping >around 64K barriers as I recall. Anyway, I can't find the specifics >now that a friend needs them :-( >QUESTION: Does anyone know the information to which I am refering? Page#? Try page 152 - the DMA address register will not generate a carry over a physical 64k boundary. > >(2) AST mentioned that there is minimal documentation for using DMA. >QUESTION: Does anyone know a pointer to more detailed doc on DMA? Nope, sorry...can't help. > >Thanks in advance >Marshall > > ________________________________________________________________ > Dr. Marshall P. Cline ARPA: cline@sun.soe.clarkson.edu > ECE Department UseNet: uunet!sun.soe.clarkson.edu!cline > Clarkson University BitNet: BH0W@CLUTX > Potsdam, NY 13676 AT&T: (315) 268-6591 >-- - Pete +---------------------------------------------------------------------------+ | | | PETER FLASS BITNET: EPRF@SNYCENVM (PREFERRED) | | DIRECTOR OF COMPUTING SERVICES INTERNET: ESCFLASS@UBVM.CC.BUFFALO.EDU | | SUNY EMPIRE STATE COLLEGE AT&TNET: (518)587-2100 X350 | | 2 UNION AVENUE | | SARATOGA SPRINGS NY 12866 "THIS SPACE FOR RENT" | | | +---------------------------------------------------------------------------+
ast@cs.vu.nl (Andy Tanenbaum) (05/17/89)
In article <CLINE.89May16114503@sun.soe.clarkson.edu> cline@sun.soe.clarkson.edu (Marshall Cline) writes: >(1) I recently read in the Minix textbook (Prentice Hall) about a DMA >caveat that AST had discovered. It had something to do with wrapping >around 64K barriers as I recall. The PC has a 16-bit DMA chip. To generate 20-bit PC bus address, it has a 4-bit register for the high-order bits. When the 16-bit counter overflows, it just wraps around, but there is no carry to the 4-bit register. Thus if you transfer 100 bytes to address 65530, the first 6 bytes go fine. At that point the 4-bit register is 0000 and the 16-bit register is all 1's. When the 16-bit counter is incremented by the DMA chip, it goes to 0. The 4-bit counter stays 0. The next 96 bytes of DMA overwrite absolute addresses 0-95 (the interrupt vectors). At the next interrupt, probably from the clock, the hardware vectors to a totally random address. This is why I always teach my students that no hardware designer should be allowed to produce any piece of hardware until 3 software guys have signed off for it. Andy Tanenbaum (ast@cs.vu.nl)
usenet@cps3xx.UUCP (Usenet file owner) (05/17/89)
in article <15600@louie.udel.EDU>, EPRF%SNYCENVM.BITNET@cornellc.cit.cornell.edu (Peter Flass) says: > On Tue, 16 May 89 15:45:03 GMT Marshall Cline said: >>(2) AST mentioned that there is minimal documentation for using DMA. >>QUESTION: Does anyone know a pointer to more detailed doc on DMA? Try calling Intel and asking for the data sheet on the 8237A. Intel (and most other chip manufacturers) will send individual data sheets for free. Distributers will usually provide that and whole books for free if it's work/sales related. To get the data sheet do: 1) Call 1-408-555-1212 2) ASk for the phone number for Intel in Santa Clara 3) Call that number 4) Tell the operator you want to talk to some one about getting a data sheet. Another source of DMA info is the IBM AT Tech Ref Manual. John H. Lawitzke UUCP: Work: ...rutgers!mailrus!frith!dale1!jhl Dale Computer Corp., R&D ...uunet!frith!dale1!jhl 2367 Science Parkway Home: ...uunet!frith!ipecac!jhl Okemos, MI, 48864 Internet: jhl@frith.egr.msu.edu