Raspberry Pi LED blinking

#include <stdint.h>

#define RPI_SYSTIMER_BASE       0x20003000UL

/* The base address of the GPIO peripheral (ARM Physical Address) */
#define GPIO_BASE       0x20200000UL

// define used GPIO pin
#define LED_GPFSEL      GPIO_GPFSEL1
#define LED_GPFBIT      18
#define LED_GPSET       GPIO_GPSET0
#define LED_GPCLR       GPIO_GPCLR0
#define LED_GPIO_BIT    16


#define GPIO_GPFSEL0    0
#define GPIO_GPFSEL1    1
#define GPIO_GPFSEL2    2
#define GPIO_GPFSEL3    3
#define GPIO_GPFSEL4    4
#define GPIO_GPFSEL5    5

#define GPIO_GPSET0     7
#define GPIO_GPSET1     8

#define GPIO_GPCLR0     10
#define GPIO_GPCLR1     11

#define GPIO_GPLEV0     13
#define GPIO_GPLEV1     14

#define GPIO_GPEDS0     16
#define GPIO_GPEDS1     17

#define GPIO_GPREN0     19
#define GPIO_GPREN1     20

#define GPIO_GPFEN0     22
#define GPIO_GPFEN1     23

#define GPIO_GPHEN0     25
#define GPIO_GPHEN1     26

#define GPIO_GPLEN0     28
#define GPIO_GPLEN1     29

#define GPIO_GPAREN0    31
#define GPIO_GPAREN1    32

#define GPIO_GPAFEN0    34
#define GPIO_GPAFEN1    35

#define GPIO_GPPUD      37
#define GPIO_GPPUDCLK0  38
#define GPIO_GPPUDCLK1  39

typedef struct {
    volatile uint32_t control_status;
    volatile uint32_t counter_lo;
    volatile uint32_t counter_hi;
    volatile uint32_t compare0;
    volatile uint32_t compare1;
    volatile uint32_t compare2;
    volatile uint32_t compare3;
} rpi_sys_timer_t;

void RPI_WaitMicroSeconds( uint32_t us );

static rpi_sys_timer_t* rpiSystemTimer = (rpi_sys_timer_t*)RPI_SYSTIMER_BASE;

/** GPIO Register set */
volatile unsigned int* gpio;

/** Main function - we'll never return from here */
int main(void)
{
    /* Assign the address of the GPIO peripheral (Using ARM Physical Address) */
    gpio = (unsigned int*)GPIO_BASE;

    /* Write 1 to the GPIO16 init nibble in the Function Select 1 GPIO
       peripheral register to enable GPIO16 as an output */
    gpio[LED_GPFSEL] |= (1 << LED_GPFBIT);

    /* Never exit as there is no OS to exit to! */
    while(1)
    {
        RPI_WaitMicroSeconds( 500000 );

        /* Set the LED GPIO pin low ( Turn OK LED on for original Pi, and off
            for plus models )*/
        gpio[LED_GPCLR] = (1 << LED_GPIO_BIT);

        RPI_WaitMicroSeconds( 500000 );

        /* Set the LED GPIO pin high ( Turn OK LED off for original Pi, and on
            for plus models )*/
        gpio[LED_GPSET] = (1 << LED_GPIO_BIT);
    }
}

void RPI_WaitMicroSeconds( uint32_t us )
{
    volatile uint32_t ts = rpiSystemTimer->counter_lo;

    while( ( rpiSystemTimer->counter_lo - ts ) < us )
    {
        /* Wait */
    }
}