blink_LED.c

#include "bbb.h"
#include "common.h"

// Four LEDs connected to GPIO1_21-24
#define LED_MASK (0xF << 21)
#define LED_PATTERN     (0xA << 21)

static void init_led_output(void)
{
    // Enable the GPIO module - CM_PER_GPIO1_CLKCTRL
    *(volatile uint32_t *)(0x44e00000 + 0xAC) = (0x1 << 18) | (0x2 << 0);

    // Enable output - GPIO1_OE
    *(volatile uint32_t *)(0x4804C000 + 0x134) &= ~LED_MASK;
}

static void heartbeat_forever(void)
{
    for (;;)
    {
        // On - GPIO1_DATAOUT
        *(volatile uint32_t *)(0x4804C000 + 0x13C) |= LED_PATTERN;
        delay(500000);

        // Off - GPIO1_DATAOUT
        *(volatile uint32_t *)(0x4804C000 + 0x13C) &= ~LED_PATTERN;
        delay(380000);

        // On
        *(volatile uint32_t *)(0x4804C000 + 0x13C) |= LED_PATTERN;
        delay(240000);

        // Off
        *(volatile uint32_t *)(0x4804C000 + 0x13C) &= ~LED_PATTERN;
        delay(2400000);
    }
}

int c_entry(void)
{
    init_led_output();
    heartbeat_forever();

    return 0;
}