mmap-issue

[Manuel Stühn]

Hi,

I'm seeing unexpected behavior using mmap( /dev/mem ) on my beaglebone 
black. It seems to me, that writing to/reading from this mapped pointer 
does not immediatly take effect. The code looks like this:

#define GPIO1   0x4804C000
#define CLR_REG 0x190
#define SET_REG 0x194
#define LED0    21
#define LED1    22
#define LED2    23
#define LED3    24

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

int pagesize = getpagesize();

volatile uint32_t* ptr =
mmap( 0, pagesize, PROT_READ | PROT_WRITE, MAP_SHARED, fd, GPIO1_ADDR );

ptr[SET_REG] = LED0 << 1;


I mapped for testing purposes the AM335x-GPIO-registers from /dev/mem.
Writing into these mmap'ed registers for toggling some LEDs does not 
immediatly take effect. I have to call it several times to get one 
LED-toggle. Is there any data caching I'm missing?

Thanks for hints.