Udo van den Heuvel wrote in a message to Mike Bilow:

 MB> In general, a device driver sees a virtual address to memory, which is
 MB> 16:16.  These addresses may have other aliases, especially when they
 MB> reflect buffers from applications in linear 0:32 space.  A device driver
 MB> uses system API calls to lock ranges of memory into some physical RAM and
 MB> then passes these physical addresses to the DMA hardware.  In some cases,
 MB> the RAM buffers may be physically discontigous, and this is compensated
 MB> for by scatter-gather hardware to do the DMA operation.

 MB> Since device drivers cannot be preempted, concurrency is not an issue.

 UvdH> Where can i get some info (sources?) for a DMA-devicedriver
 UvdH> which I can use for my own setup?

The only real reference is the IBM OS/2 Device Driver Kit, sold as an
add-on to the DevCon subscription.  The DDK comes with full source to most
of the drivers provided with OS/2, including several that use DMA such as
IBM1FLPY.ADD and IBM1S506.ADD.  These are BASEDEVs rather than DEVICEs, and
this makes them considerably more complicated.  An ADD is also among the
more complicated type of BASEDEV, second only to a DMD.  Basically, as long
as your device is not part of the boot process, you would not have to worry
about the added complexity of a BASEDEV.  Unfortunately, I can't think of
any examples of drivers which use DMA but which are not BASEDEVs.
 
-- Mike


---