Re: mmap going to wrong physical address

Bill Davidsen
2004-11-05T15:28:24Z

mark slutz wrote:
> I am writting an application that needs control over large (1gig+)
> portions of contiguous memory. I am currently doing this by using
> mem=1024m during boot. My system is a dual opteron with 5 gig of
> memory. In my program I have
>
> if ((fd=open("/dev/mem", O_RDWR))<0)
> {
> perror("open");
> exit(-1);
> }
>
>
> PtrMemoryBase = (void *) mmap64(
> NULL,
> size,
> PROT_READ | PROT_WRITE,
> MAP_FILE | MAP_SHARED,
> fd,
> base );
>
> size = 1MB
>
> I also have -D_FILE_OFFSET_BITS=64.
>
> If base is between 1 and 3 gig the process works fine. When base is 4
> gig + the mmap64 works but the memory does not seem to be mapped to
> the base location. I write a pattern to PtrMemoryBase then have my
> hardware start doing DMA transfers from the base address but I do not
> get the data I wrote to PtrMemoryBase.
>
> Thanks for any help

I'm not sure it will help, but have you tried the MAP_FIXED option, and
is your address which doesn't work a multiple of the page size?

--
-bill davidsen (davidsen@tmr.com)
"The secret to procrastination is to put things off until the
last possible moment - but no longer" -me