edhall@randvax.UUCP (Ed Hall) (03/09/89)
I'm developing (for my own education) an AT interface card using DMA for data transfers. I know how to do this for PC's, and by extention, how to do 8-bit DMA interfaces for the AT. But what is different about the 16-bit channels on the AT? For instance, I know that the second DMA controller (channels 5 through 7) control address lines A1-A16, thus covering a 128K window of two-byte words. Other than this, what is different about 16-bit DMA? Is the MEM CS16 signal asserted by the AT during DMA reads? Writes? How about I/O CS16? What is the layout of the channel 5-7 page registers? I've got piles of documentation but nothing answers these particular questions. Help me graduate from 8 to 16 bits! Answers or pointers to documentation are both appreciated. -Ed Hall edhall@rand.org uunet!sdcrdcf!randvax!edhall
tchu@bbn.com (Tom Chu) (03/10/89)
In article <1901@randvax.UUCP> edhall@randvax.UUCP (Ed Hall) writes: >I'm developing (for my own education) an AT interface card using >DMA for data transfers. I know how to do this for PC's, and by >extention, how to do 8-bit DMA interfaces for the AT. But what >is different about the 16-bit channels on the AT? > >For instance, I know that the second DMA controller (channels 5 through >7) control address lines A1-A16, thus covering a 128K window of two-byte >words. Other than this, what is different about 16-bit DMA? Is the MEM >CS16 signal asserted by the AT during DMA reads? Writes? How about I/O >CS16? What is the layout of the channel 5-7 page registers? > >I've got piles of documentation but nothing answers these particular >questions. Help me graduate from 8 to 16 bits! Answers or pointers >to documentation are both appreciated. > > -Ed Hall > edhall@rand.org > uunet!sdcrdcf!randvax!edhall Unless you want to do things very slowly do not use DMA !! The DMA on the PC-AT is very slow. In fact the only device that I know of that uses DMA is the floppy controller. The DMA circuitry of the PC-AT is running at 5 MHZ (I think, but it has been awhile since I looked at a PC-AT). Hard disks on the PC-AT use MOVE strings, software to move data to and from the hard disk. I/O_CS_16, MEM_CS_16 are signals controlled by peripheral boards to indicate that the current I/O more Memory access is a 16 bit access. The 80286 has to types of address space, a memory and an I/O space. In real mode the 80286 has an address capability of 1 megabyte and an I/O address space of 64K. Accessing memory basically uses MOVE instructions and I/O accesses require INPUT and OUTPUT instructions. So in conclusion, don't use the DMA !! DMA Performance on the AT really bites the big one !!! T. Chu
abcscnge@csuna.csun.edu (Scott "The Pseudo-Hacker" Neugroschl) (03/12/89)
In article <37068@bbn.COM> tchu@BBN.COM (Tom Chu) writes:
#Unless you want to do things very slowly do not use DMA !! The DMA on the PC-AT
#is very slow. In fact the only device that I know of that uses DMA is the
#floppy controller. The DMA circuitry of the PC-AT is running at 5 MHZ (I think,
#but it has been awhile since I looked at a PC-AT). Hard disks on the PC-AT use
#MOVE strings, software to move data to and from the hard disk.
#
#I/O_CS_16, MEM_CS_16 are signals controlled by peripheral boards to indicate
#that the current I/O more Memory access is a 16 bit access. The 80286 has to
#types of address space, a memory and an I/O space. In real mode the 80286 has
#an address capability of 1 megabyte and an I/O address space of 64K. Accessing
#memory basically uses MOVE instructions and I/O accesses require INPUT and
#OUTPUT instructions.
#
#So in conclusion, don't use the DMA !! DMA Performance on the AT really bites
#the big one !!!
#
This is true only under DOS. When writing/designing something to be used
under a multi-tasking system (can you say UNIX? or even OS/2? :-), one must
be careful not to hog the MOST PRECIOUS RESOURCE IN THE SYSTEM -- to wit, the
CPU. Granted IBM really blew it with their DMA design in the AT, but
it should still be used for multitasking! This unburdens the CPU and also
lowers the period of time that the CPU runs with interrupts locked out.
Any Xenix users out there want to talk about losing RS-232 interrupts during
disk access because of this?
--
Scott "The Pseudo-Hacker" Neugroschl
UUCP: ...!sm.unisys.com!csun!csuna.csun.edu!abcscnge
-- unless explicitly stated above, this article not for use by rec.humor.funny
-- Disclaimers? We don't need no stinking disclaimers!!!davidsen@steinmetz.ge.com (William E. Davidsen Jr) (03/15/89)
In article <1751@csuna.csun.edu> abcscnge@csuna.csun.edu (Scott Neugroschl) writes: | Any Xenix users out there want to talk about losing RS-232 interrupts during | disk access because of this? I do. I run an original AT with xenix 2.1.3, with input coming in at 2400, 9600, and via ethernet. I have never seen any indication of lost interrupts. I also run a 386 at home, 2.3.1, with two 2400 lines and a 9600, all on dumb ports. No problem. Where have you seen this? | Scott "The Pseudo-Hacker" Neugroschl | UUCP: ...!sm.unisys.com!csun!csuna.csun.edu!abcscnge -- bill davidsen (wedu@ge-crd.arpa) {uunet | philabs}!steinmetz!crdos1!davidsen "Stupidity, like virtue, is its own reward" -me
mlawless@ncrwic.Wichita.NCR.COM (Mike Lawless) (03/15/89)
In article <37068@bbn.COM> tchu@BBN.COM (Tom Chu) writes: > >Unless you want to do things very slowly do not use DMA !! The DMA on the PC- >is very slow. In fact the only device that I know of that uses DMA is the >floppy controller. The DMA circuitry of the PC-AT is running at 5 MHZ (I thin >but it has been awhile since I looked at a PC-AT). Hard disks on the PC-AT us >MOVE strings, software to move data to and from the hard disk. I have heard this before, but I wonder if this is true of all AT-class machines, or just the ones from Big Blue and those that closely follow that design. For instance, is DMA performance any better on a typical 10-12 Mhz At compatible machine using the Chips and Techologies chipset rather than the antique Intel 8237? Are there other proprietary DMA designs out there that are faster? Inquiring minds want to know. -- Mike Lawless, NCR E&M Wichita, Box 20 (316) 636-8666 (NCR: 654-8666) 3718 N. Rock Road, Wichita, KS 67226 Mike.Lawless@Wichita.NCR.COM {ece-csc,hubcap,gould,rtech}!ncrcae!ncrwic!Mike.Lawless {sdcsvax,cbatt,dcdwest,nosc.ARPA}!ncr-sd!ncrwic!Mike.Lawless