Issues mmaping the same file twice

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I'm using a Raspberry Pi B+, and I'm trying to mmap two different sections of /dev/mem - the first to be able to set two pins' functions from location 0x2020 0004 (0x04 bytes long), the other to manipulate the BSC Slave functions on the BCM2835 chip on the Pi from location 0x2021 4000 (0x1C bytes long).

static uint32_t * initMapMem(int fd, uint32_t addr, uint32_t len)
{
    return (uint32_t *) mmap((void*)0x0, len,
       PROT_READ|PROT_WRITE|PROT_EXEC,
       MAP_SHARED|MAP_LOCKED,
       fd, addr);
}

int initialise(void) {
   int fd;

   fd = open("/dev/mem", O_RDWR | O_SYNC) ;

   if (fd < 0)
   {
      fprintf(stderr, "This program needs root privileges.  Try using sudo.\n");
      return 1;
   }

   pinReg = initMapMem(fd, 0x20200004, 0x4);
   bscReg = initMapMem(fd, 0x20214000, 0x1C);

   close(fd);

   if (bscReg == MAP_FAILED)
   {
      fprintf(stderr, "Bad, mmap failed.\n");
      return 1;
   }
   if (pinReg == MAP_FAILED)
   {
      fprintf(stderr, "Bad, mmap failed.\n");
      return 1;
   }
   return 0;
}

initialise() is called out of main(). Stepping through the program with gdb I find that bscReg gets positioned right, but pinReg returns as MAP_FAILED (aka 0xFFFFFFFF) with errno set to EINVAL. Doesn't matter which way it's done, either - pinReg always finds itself as MAP_FAILED when mmaped first or second.

How do I get pinReg to a valid value?

asked 1 min ago

sctjkc01

26

Issues mmaping the same file twice