On Tue, May 07, 2013 at 06:35:43AM +0000, Warlich, Christof wrote:
[...]
> Furthermore, read / write access through a simple program using /dev/mem
> _does_ work as expected:
>
> #include <unistd.h>
> #include <stdio.h>
> #include <fcntl.h>
> #include <assert.h>
> #include <sys/mman.h>
> int main( int argc, char *argv[]) {
> char *mem;
> int fd;
> fd = open ("/dev/mem", O_RDWR);
> assert(fd >= 0);
> mem = mmap(NULL, getpagesize(), PROT_READ|PROT_WRITE, MAP_SHARED, fd, (off_t) 0x81423000);
> assert(mem != MAP_FAILED);
> printf("Memory pointer: %p\n", mem);
> printf("The PCI memory is : %#x\n", *mem);
> *mem = *argv[1];
> printf("The PCI memory is : %#x\n", *mem);
> munmap(mem, getpagesize());
> close(fd);
> return 0;
> }
>
> Calling it, yields:
>
> $ led 4
> Memory pointer: 0xb7678000
> The PCI memory is : 0x33
> The PCI memory is : 0x34
>
> And the LED matrix display being behind that address switches from 3 to
> 4 as expected.
>
> Thus, I still cannot see why the access through /dev/mem using dd doesn't
> work.
I suspect dd uses read instead of mmap.
Thanks,
Jonathan Neuschäfer
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