*** Answering a msg posted in area PERSONAL_MAIL (Personal Mail).

Hello Mike!

 UvdH>> When I set up the DMA chips to write to a buffer, how does
 UvdH>> this work when another task is being serviced?
 UvdH>> Is the memory protection a problem?
 UvdH>> What other caveats are to be taken care of? (this is OS/2,
 UvdH>> not MS-DOS)
 MB> Under OS/2, you can only do DMA from a device driver running in Ring
 MB> 0. I'll assume you understand that.

More or less, yes.

 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.

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


Greetz,
        Udo

---