Re: Writing/Reading GPIO on AT91SAM9260ek

[Adam Yergovich <ayergo@xxxxxxxxxxx>]

Paul Kavan wrote:

> Thanks for the info. So, if I cannot use those definitions, any idea
> of how to access the gpio pins from userspace?

I know this was different for me as well coming from the old DOS 
standpoint.  The trick to remember is that memory (and therefore 
hardware) is going through a transformation-layer to allow the kernel to 
better keep track of things.

For accessing I/O, this means we need a way to map back and forth.  This 
usually involves opening the device /dev/mem and using the "mmap" 
function to get a pointer for use.  Something like this:


if((mem = open ("/dev/mem", O_RDWR | O_SYNC))== -1){
  printf("Cannot open /dev/mem! \n");
  exit(-1);
}
map_base = mmap(0, MAP_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, mem, 
target & ~MAP_MASK);
if( map_base == (void *)-1){
printf("mmap error!");
exit(-1);
}

virt_addr=map_base + (target & MAP_MASK);
readval = *((unsigned long *) virt_addr);

printf("Value:");
printf("%x", readval);

Hope this is of some use,

-Adam


--
Adam Yergovich
Engineer
JK Microsystems

1403 Fifth St. Suite D
Davis, CA 95616

Tel:(530) 297-6073

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