On 19-11-07 15:51, Erik Mouw wrote:
On Fri, Nov 16, 2007 at 12:01:40AM -0800, Mohammad M Molla wrote:
I am a bit confused by the relation between a DMA controller and
device - (let's say NIC) support of DMA.
My questions are -
1. Is it possible to perform DMA operation on a system without any
central DMA controller?
Yes, many PCI devices can do busmaster DMA. Check the output of "lspci
-vvv" and look for "BusMaster+".
And adding a bit to that -- in the PC, for anything but old ISA (*), devices
doing their own DMA ("being a busmaster") is also the norm. There have been
PCI devices, soundcards at least, that used the old legacy DMA controller
but only as a backwards compatibility hack really. The central "motherboard
DMA" controller is in essence only available to ISA and is obsolete.
(*) well, ISA or "LPC", which stands for "Legacy PC" and is rebranded ISA,
introduced when motherboards lost real ISA but retained devices such as the
legacy serial and parallel ports and floppy-controller. Of these, the floppy
and (EPC) parallel port can use DMA.
Rene.
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