GPIOB->BSRR = (1UL << LED_PIN);

bit  0~15 : Set
bit 16~31 : Reset

GPIOB->BSRR = (1UL << 0);
GPIOB->BSRR = (1UL << 16);

main.c  → 무엇을 할지
gpio.c  → GPIO를 어떻게 제어할지
gpio.h  → 외부에 공개할 interface

Ch07_gpio/
├── Inc/
│   └── gpio.h
└── Src/
    ├── gpio.c
    └── main.c

#ifndef GPIO_H
#define GPIO_H
#include <stdbool.h>
/* ---- LED (PB0, LD1 녹색) ---- */
void led_init(void);
void led_on(void);
void led_off(void);
/* ---- Push Button (PC13, B1) ---- */
void button_init(void);
bool get_btn_state(void);
#endif /* GPIO_H */

#include "stm32f4xx.h"
#include "gpio.h"
#define LED_PIN    0U   /* PB0 = LD1 (녹색) /
#define BTN_PIN    13U  / PC13 = B1 */
void led_init(void)
{
RCC->AHB1ENR |= RCC_AHB1ENR_GPIOBEN;
GPIOB->MODER &= ~(0x3UL << (LED_PIN * 2));
GPIOB->MODER |=  (0x1UL << (LED_PIN * 2));

}
void led_on(void)
{
GPIOB->BSRR = (1UL << LED_PIN);        /* Set */
}
void led_off(void)
{
GPIOB->BSRR = (1UL << (LED_PIN + 16)); /* Reset */
}
void button_init(void)
{
RCC->AHB1ENR |= RCC_AHB1ENR_GPIOCEN;
GPIOC-&gt;MODER &amp;= ~(0x3UL &lt;&lt; (BTN_PIN * 2));  /* Input */
GPIOC-&gt;PUPDR &amp;= ~(0x3UL &lt;&lt; (BTN_PIN * 2));  /* No pull (보드가 자체 처리) */

}
bool get_btn_state(void)
{
return (GPIOC->IDR & (1UL << BTN_PIN)) != 0U;  /* active-HIGH */
}

#include "gpio.h"
int main(void)
{
bool btn_state;
led_init();
button_init();

while (1)
{
    btn_state = get_btn_state();

    if (btn_state)
    {
        led_on();
    }
    else
    {
        led_off();
    }
}

}

GPIOB->BSRR = (1UL << LED_PIN);

GPIOB->BSRR = (1UL << (LED_PIN + 16));

return (GPIOC->IDR & (1UL << BTN_PIN)) != 0U;

B1
│
▼
PC13
│
▼
GPIOC->IDR
│
▼
get_btn_state()
│
├─ true  → led_on()
│
└─ false → led_off()
│
▼
GPIOB->BSRR
│
▼
PB0
│
▼
LD1

text = 800 bytes
data = 0 bytes
bss  = 2560 bytes