SCB->SCR.SLEEPDEEP
= Cortex-M core에게 deep sleep 요청
PWR->CR.PDDS
= STM32에게 deep sleep 중 Standby 선택

__WFI();

Normal boot
│
├─ UART init
├─ LED init
├─ PA0 wakeup pin init
└─ reset source 확인
│
▼
B1 / EXTI13
│
▼
LED OFF
│
▼
Standby setup
│
├─ WUF clear
├─ WKUP enable
├─ PDDS
├─ SLEEPDEEP
└─ __WFI()
│
▼
Standby
│
PA0 wakeup
│
▼
Reset
│
▼
main()

Ch18_pm/
├── Inc/gpio.h
├── Src/gpio.c
├── Inc/gpio_exti.h
├── Src/gpio_exti.c
├── Inc/standby_mode.h
├── Src/standby_mode.c
├── Inc/uart.h
├── Src/uart.c
├── Src/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);
void led_toggle(void);   /* Ch08에서 추가 */
#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 */
}
void led_toggle(void)
{
GPIOB->ODR ^= (1UL << 0);  /* PB0 = LD1 */
}

#ifndef GPIO_EXTI_H__
#define GPIO_EXTI_H__
#include <stdint.h>
#include "stm32f4xx.h"
#define LINE13 (1U << 13)
void pc13_exti_init(void);
#endif

#include "gpio_exti.h"
#define GPIOCEN   (1U << 2)
#define SYSCFGEN  (1U << 14)
void pc13_exti_init(void)
{
__disable_irq();
RCC-&gt;AHB1ENR |= GPIOCEN;

GPIOC-&gt;MODER &amp;= ~(1U &lt;&lt; 26);
GPIOC-&gt;MODER &amp;= ~(1U &lt;&lt; 27);

RCC-&gt;APB2ENR |= SYSCFGEN;

/* EXTI13 -&gt; PORTC */
SYSCFG-&gt;EXTICR[3] |= (1U &lt;&lt; 5);

EXTI-&gt;IMR |= (1U &lt;&lt; 13);

/* 이 보드는 B1이 active-HIGH라 Rising-edge (원서는 FTSR/active-LOW) */
EXTI-&gt;RTSR |= (1U &lt;&lt; 13);

NVIC_EnableIRQ(EXTI15_10_IRQn);

__enable_irq();

}

#ifndef STANDBY_MODE_H__
#define STANDBY_MODE_H__
#include <stdint.h>
#include "stm32f4xx.h"
uint32_t get_wakeup_pin_state(void);
void wakeup_pin_init(void);
void standby_wakeup_pin_setup(void);
#endif /* STANDBY_MODE_H__ */

#include "standby_mode.h"
#define PWR_MODE_STANDBY  (PWR_CR_PDDS)
#define WK_PIN            (1U << 0)
static void set_power_mode(uint32_t pwr_mode);
void wakeup_pin_init(void)
{
RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN;
GPIOA-&gt;MODER &amp;= ~(1U &lt;&lt; 0);
GPIOA-&gt;MODER &amp;= ~(1U &lt;&lt; 1);

GPIOA-&gt;PUPDR &amp;= ~(1U &lt;&lt; 0);
GPIOA-&gt;PUPDR &amp;= ~(1U &lt;&lt; 1);

}
uint32_t get_wakeup_pin_state(void)
{
return ((GPIOA->IDR & WK_PIN) == WK_PIN);
}
static void set_power_mode(uint32_t pwr_mode)
{
MODIFY_REG(PWR->CR,
(PWR_CR_PDDS | PWR_CR_LPDS | PWR_CR_FPDS | PWR_CR_LPLVDS | PWR_CR_MRLVDS),
pwr_mode);
}
void standby_wakeup_pin_setup(void)
{
while (get_wakeup_pin_state() == 0) {}
PWR-&gt;CSR &amp;= ~(1U &lt;&lt; 8);
PWR-&gt;CR  |= (1U &lt;&lt; 2);
PWR-&gt;CSR |= (1U &lt;&lt; 8);

set_power_mode(PWR_MODE_STANDBY);

SCB-&gt;SCR |= (1U &lt;&lt; 2);

__WFI();

}

#ifndef UART_H
#define UART_H
#include "stm32f4xx.h"
void uart_init(void);
void uart_write_string(const char *s);
int __io_putchar(int ch);
#endif

#include <stdint.h>
#include "uart.h"
#define GPIODEN    (1U << 3)
#define USART3EN   (1U << 18)
#define DBG_UART_BAUDRATE 115200U
#define SYS_FREQ           16000000U
#define APB1_CLK           SYS_FREQ
#define CR1_TE   (1U << 3)
#define CR1_UE   (1U << 13)
#define SR_TXE   (1U << 7)
static void uart_write(int ch);
static uint16_t compute_uart_bd(uint32_t periph_clk, uint32_t baudrate);
static void uart_set_baudrate(uint32_t periph_clk, uint32_t baudrate);
int __io_putchar(int ch)
{
uart_write(ch);
return ch;
}
void uart_init(void)
{
RCC->AHB1ENR |= GPIODEN;
GPIOD-&gt;MODER &amp;= ~(0x3UL &lt;&lt; (8 * 2));
GPIOD-&gt;MODER |=  (0x2UL &lt;&lt; (8 * 2));
GPIOD-&gt;MODER &amp;= ~(0x3UL &lt;&lt; (9 * 2));
GPIOD-&gt;MODER |=  (0x2UL &lt;&lt; (9 * 2));

GPIOD-&gt;AFR[1] &amp;= ~(0xFUL &lt;&lt; 0);
GPIOD-&gt;AFR[1] |=  (0x7UL &lt;&lt; 0);   /* PD8 -&gt; AF7 (USART3_TX) */
GPIOD-&gt;AFR[1] &amp;= ~(0xFUL &lt;&lt; 4);
GPIOD-&gt;AFR[1] |=  (0x7UL &lt;&lt; 4);   /* PD9 -&gt; AF7 (USART3_RX) */

RCC-&gt;APB1ENR |= USART3EN;

uart_set_baudrate(APB1_CLK, DBG_UART_BAUDRATE);

USART3-&gt;CR1 = CR1_TE;
USART3-&gt;CR1 |= CR1_UE;

}
static void uart_write(int ch)
{
while (!(USART3->SR & SR_TXE)) { }
USART3->DR = (ch & 0xFF);
}
void uart_write_string(const char *s)
{
while (*s) uart_write((int)*s++);
}
static uint16_t compute_uart_bd(uint32_t periph_clk, uint32_t baudrate)
{
return (uint16_t)((periph_clk + (baudrate / 2U)) / baudrate);
}
static void uart_set_baudrate(uint32_t periph_clk, uint32_t baudrate)
{
USART3->BRR = compute_uart_bd(periph_clk, baudrate);
}

/*

Ch18 - Power Management: Standby 모드 + PA0(WKUP) 웨이크업


B1(PC13)을 누르면 EXTI 인터럽트로 standby_wakeup_pin_setup()이
호출되어 보드가 Standby 모드(가장 깊은 저전력 모드)로 들어간다.
PA0(WKUP)에 배선된 신호가 Low->High로 바뀌면 보드가 깨어나는데,
Standby에서 깨어나는 건 완전한 리셋과 동일해서 main()이 처음부터
다시 실행된다 — 그래서 check_reset_source()가 PWR->CSR의 SBF
비트로 "방금 Standby에서 깨어났다"를 판별한다.


LD1(PB0)은 배선 불필요. 정상 동작 중엔 켜져 있다가 Standby 진입
직전에 꺼지고, 웨이크업(리셋) 후 다시 켜진다.
*/
#include "gpio.h"
#include "gpio_exti.h"
#include "standby_mode.h"
#include "uart.h"

uint8_t g_btn_press;
static void check_reset_source(void);
int main(void)
{
uart_init();
led_init();
wakeup_pin_init();
/* 리셋 원인 확인 (Standby에서 깨어난 것인지 아닌지) */
check_reset_source();

/* 정상 동작 중임을 LED로 표시 */
led_on();

/* B1 버튼으로 Standby 진입을 트리거하기 위한 EXTI 설정 */
pc13_exti_init();

while (1)
{
    /* 모든 동작은 인터럽트(B1 -> Standby 진입, WKUP -> 리셋)로만 이뤄짐 */
}

}
static void check_reset_source(void)
{
RCC->APB1ENR |= RCC_APB1ENR_PWREN;
if ((PWR->CSR & PWR_CSR_SBF) == PWR_CSR_SBF)
{
    PWR->CR |= PWR_CR_CSBF;
    uart_write_string("System resume from Standby.....\r\n");

    while (get_wakeup_pin_state() == 0) {}
}

if ((PWR->CSR & PWR_CSR_WUF) == PWR_CSR_WUF)
{
    PWR->CR |= PWR_CR_CWUF;
}

}
static void exti_callback(void)
{
led_off();
standby_wakeup_pin_setup();
}
void EXTI15_10_IRQHandler(void)
{
if ((EXTI->PR & LINE13) != 0)
{
EXTI->PR |= LINE13;
exti_callback();
}
}

text = 1660 bytes
data = 0 bytes
bss  = 2560 bytes
warning 없음

while (get_wakeup_pin_state() == 0) {}