From owner-freebsd-hackers  Fri Oct 23 07:05:51 1998
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Date: Fri, 23 Oct 1998 08:05:14 -0600
From: vanmaren@fast.cs.utah.edu (Kevin Van Maren)
Message-Id: <199810231405.IAA16725@fast.cs.utah.edu>
To: Etienne.Debruin@KryptoKom.DE, freebsd-hackers@FreeBSD.ORG
Subject: Re:  Q: bus mastering
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> hi, i paged through the mail list archives but could not find a specific
> technical discussion about bus mastering.  i would like to implement bus
> mastering for a pci device driver.  need more info...
> 
> eT

This is highly device-dependant.  Each bus-master-capable PCI
device has its own DMA controller, and they are all programmed
in a device-specific manner.  It is not at all like ISA, where
there is a centralized DMA controller that is used for DMA
transfers.  As a good start, you can grep for "vtophys" in
src/sys/pci/*.c, but a better bet would be to get the programming
info for the specific device you are interested in.  (Many of
the ethernet devices, especially, support scatter-gather DMA).

Good luck.
Kevin Van Maren

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