#include <stdint.h>
#include <rom/ets_sys.h>

// ESP32 GPIO register addresses
#define GPIO_OUT_REG      (*(volatile uint32_t*)0x3FF44004)
#define GPIO_OUT_W1TS_REG (*(volatile uint32_t*)0x3FF44008)
#define GPIO_OUT_W1TC_REG (*(volatile uint32_t*)0x3FF4400C)
#define GPIO_ENABLE_REG   (*(volatile uint32_t*)0x3FF44020)
#define GPIO_IN_REG       (*(volatile uint32_t*)0x3FF4403C)

#define LED_PIN     2
#define SWITCH_PIN  4

void delay_ms(uint32_t ms) {
    while (ms--) {
        ets_delay_us(1000);
    }
}

void app_main(void) {

    // Set GPIO2 as output
    GPIO_ENABLE_REG |= (1u << LED_PIN);

    // Set GPIO4 as input
    GPIO_ENABLE_REG &= ~(1u << SWITCH_PIN);

    while (1) {

        // Read GPIO4
        if (GPIO_IN_REG & (1u << SWITCH_PIN)) {
            // If switch input = 1, turn LED ON
            GPIO_OUT_W1TS_REG = (1u << LED_PIN);
        } else {
            // If switch input = 0, turn LED OFF
            GPIO_OUT_W1TC_REG = (1u << LED_PIN);
        }

        delay_ms(50);
    }
}