c - Issues mmaping the same file twice -


i'm using raspberry pi b+, , i'm trying mmap 2 different sections of /dev/mem - first able set 2 pins' functions location 0x2020 0004 (0x04 bytes long), other manipulate bsc slave functions on bcm2835 chip on pi 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() called out of main(). stepping through program gdb find bscreg gets positioned right, pinreg returns map_failed (aka 0xffffffff) errno set einval. doesn't matter way it's done, either - pinreg finds map_failed when mmaped first or second.

how pinreg valid value?

the first mmap() failing because offset you're trying map (0x20200004) isn't page-aligned. create mapping @ 0x20200000 size of @ least 8, write @ offset of 0x4.


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