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gpio-baremetal

gpio-baremetal

github.com/mohitmishra786Development269306 installsUpdated 18w ago
Repository

About gpio-baremetal

gpio-baremetal guides developers through configuring GPIO without a HAL, including pin modes, alternate functions, pull resistors, and interrupts. It covers STM32 patterns as well as notes for nRF52 and ESP32.

Key features

  1. 01Input and output configuration
  2. 02Alternate-function pin mapping
  3. 03Pull-up and pull-down setup
  4. 04Pin-change interrupt configuration
  5. 05STM32, nRF52, and ESP32 examples

Use cases

  1. 01Blinking an LED or reading a button
  2. 02Mapping pins to USART or SPI
  3. 03Configuring edge-triggered EXTI interrupts
  4. 04Porting GPIO code between vendors

Install

Copy the command and run it in a terminal.

$npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill gpio-baremetal

After installing, type/gpio-baremetalin Claude Code to confirm it loaded.

Details

From the project README

GPIO (Bare-Metal)

Purpose

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.

When to Use

  • 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

Workflow

1. STM32 GPIO pattern
/* 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 */
2. Input with pull-up
/* 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)
/* 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.

4. nRF52 / ESP32 notes
PlatformPattern
nRF52NRF_P0->PIN_CNF[n] — direction, pull, drive
ESP32GPIO.out_w1ts, GPIO.enable; IO_MUX for function

Always enable peripheral clock / power domain before pin config.

5. Agent usage
/gpio-baremetal Configure PA2 as USART2 TX alternate function on STM32F4

Common Problems

SymptomCauseFix
Pin stuckWrong MODER / not AFRe-read RM pin table
EXTI stormNo debounce / floating inputEnable pull; debounce in software
AF mismatchWrong AFR nibblePin-specific AF table in RM
No toggle visibleWrong port bit / LED active lowCheck schematic

Related Skills

  • skills/baremetal/mmio-and-bit-manipulation — BSRR/MODER masks
  • skills/baremetal/peripherals-from-datasheet — RM pinout tables
  • skills/baremetal/uart-serial-baremetal — AF mux for serial

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