At 07:08 AM 8/31/99 -0700, Estabridis, Janet P wrote:
>I have gotten shared memory to work on this machine but my shared memory
>block size was small, about 700 bytes to test out my code. Now I was ready
>to increase it and I get a Segmenation Fault when I /sbin/insmod my rt
>process....
My experiences may help:
I am doing DMA transfers from a PCI card directly to shared RAM while
within an RT module. Also while in the module, I write a couple of
locations in shared-RAM directly.
At first, I was doing this with a 1MB shared-RAM area and all this seemed
to work. But I got core dumps when I changed the shared-RAM size to 4MB!
Cause: I was following the shared-memory FAQ which didn't mention the need
to use vremap(). Once I did the vremap() call before touching shared-RAM,
my problems went away. I guess that when I was using the 1 MB area, I was
simply lucky.
So: I can apparently DMA to shared-RAM without performing a vremap()
because the transfer occurs outside the CPU. But programmed reads/writes
must be done using a mapped pointer.
Hoping this helps,
Marshall Jose, WA3VPZ
Johns Hopkins Univ. Applied Physics Lab., 240-228-4367
| "It could have been an organically based disturbance of the brain -- |
| perhaps a tumor or a metabolic deficiency -- but after a thorough |
| neurological exam it was determined that Byron was simply a jerk." |
| -- Jeff Jahnke, runner-up, 7th Annual Bulwer-Lytton Contest. |
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