gpio-baremetal

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GPIO (Bare-Metal)

GPIO（裸机）

Purpose

用途

Configure and use GPIO without HAL: input/output modes, alternate function mapping, pull-up/down, speed/slew, and pin-change interrupts for LEDs, buttons, and peripheral pin mux.

无需HAL库即可配置和使用GPIO：包括LED、按钮和外设引脚复用的输入/输出模式、复用功能映射、上拉/下拉、速度/压摆率以及引脚变化中断。

When to Use

使用场景

Blink LED or read button before bringing up UART/SPI
Mux pins to USART/SPI alternate functions
EXTI line interrupts on pin edges
Porting GPIO code between vendors

在启用UART/SPI之前实现LED闪烁或按钮读取
将引脚复用到USART/SPI复用功能
引脚边沿触发的EXTI线中断
在不同厂商的MCU之间移植GPIO代码

Workflow

工作流程

1. STM32 GPIO pattern

1. STM32 GPIO编程范式

/* Enable GPIOA clock */
RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN;

/* PA5 output — MODER[11:10] = 01 */
GPIOA->MODER &= ~(3U << (5 * 2));
GPIOA->MODER |=  (1U << (5 * 2));

/* Toggle via BSRR — atomic set/reset */
GPIOA->BSRR = (1U << 5);       /* set */
GPIOA->BSRR = (1U << (5+16));  /* reset */

Alternate function (e.g., USART2 TX on PA2):

GPIOA->MODER &= ~(3U << (2*2));
GPIOA->MODER |=  (2U << (2*2));           /* AF mode */
GPIOA->AFR[0] &= ~(0xFU << (2*4));
GPIOA->AFR[0] |=  (7U << (2*4));          /* AF7 = USART2 */

/* Enable GPIOA clock */
RCC->AHB1ENR |= RCC_AHB1ENR_GPIOAEN;

/* PA5 output — MODER[11:10] = 01 */
GPIOA->MODER &= ~(3U << (5 * 2));
GPIOA->MODER |=  (1U << (5 * 2));

/* Toggle via BSRR — atomic set/reset */
GPIOA->BSRR = (1U << 5);       /* set */
GPIOA->BSRR = (1U << (5+16));  /* reset */

复用功能（例如，PA2作为USART2 TX引脚）：

GPIOA->MODER &= ~(3U << (2*2));
GPIOA->MODER |=  (2U << (2*2));           /* AF mode */
GPIOA->AFR[0] &= ~(0xFU << (2*4));
GPIOA->AFR[0] |=  (7U << (2*4));          /* AF7 = USART2 */

2. Input with pull-up

2. 上拉输入配置

/* PC13 input, pull-up */
GPIOC->MODER &= ~(3U << (13*2));          /* input mode 00 */
GPIOC->PUPDR &= ~(3U << (13*2));
GPIOC->PUPDR |=  (1U << (13*2));          /* pull-up */

int pressed = !(GPIOC->IDR & (1U << 13)); /* active low */

/* PC13 input, pull-up */
GPIOC->MODER &= ~(3U << (13*2));          /* input mode 00 */
GPIOC->PUPDR &= ~(3U << (13*2));
GPIOC->PUPDR |=  (1U << (13*2));          /* pull-up */

int pressed = !(GPIOC->IDR & (1U << 13)); /* active low */

3. EXTI interrupt (STM32)

3. EXTI中断（STM32）

/* SYSCFG: map EXTI13 to PC13 */
SYSCFG->EXTICR[3] = (SYSCFG->EXTICR[3] & ~0xFU) | 0x2;  /* port C */
EXTI->IMR  |= (1U << 13);
EXTI->FTSR |= (1U << 13);  /* falling edge */
NVIC_EnableIRQ(EXTI15_10_IRQn);

ISR: check

EXTI->PR

, clear with write-1.

/* SYSCFG: map EXTI13 to PC13 */
SYSCFG->EXTICR[3] = (SYSCFG->EXTICR[3] & ~0xFU) | 0x2;  /* port C */
EXTI->IMR  |= (1U << 13);
EXTI->FTSR |= (1U << 13);  /* falling edge */
NVIC_EnableIRQ(EXTI15_10_IRQn);

中断服务程序（ISR）：检查

EXTI->PR

寄存器，通过写1操作清除中断标志。

4. nRF52 / ESP32 notes

4. nRF52 / ESP32 注意事项

Platform	Pattern
nRF52	`NRF_P0->PIN_CNF[n]` — direction, pull, drive
ESP32	`GPIO.out_w1ts` , `GPIO.enable` ; IO_MUX for function

Always enable peripheral clock / power domain before pin config.

平台	编程范式
nRF52	`NRF_P0->PIN_CNF[n]` — 方向、上拉/下拉、驱动能力
ESP32	`GPIO.out_w1ts` 、 `GPIO.enable` ；使用IO_MUX配置功能

引脚配置前务必启用外设时钟/电源域。

5. Agent usage

5. Agent 使用方式

/gpio-baremetal Configure PA2 as USART2 TX alternate function on STM32F4

/gpio-baremetal Configure PA2 as USART2 TX alternate function on STM32F4

Common Problems

常见问题

Symptom	Cause	Fix
Pin stuck	Wrong MODER / not AF	Re-read RM pin table
EXTI storm	No debounce / floating input	Enable pull; debounce in software
AF mismatch	Wrong AFR nibble	Pin-specific AF table in RM
No toggle visible	Wrong port bit / LED active low	Check schematic

症状	原因	解决方法
引脚状态异常	MODER配置错误/未设置复用功能	重新查阅参考手册（RM）引脚表
EXTI中断风暴	未消抖/输入引脚浮空	启用上拉/下拉；软件消抖
复用功能不匹配	AFR四位域配置错误	查看参考手册（RM）中引脚专属复用表
LED无闪烁效果	端口位选择错误/LED低电平有效	检查原理图