How to use
- Copy the installation command and review the source package before installing it in your own agent environment.
- Check the source document for required tools, credentials and supported hosts.
- Describe your input and desired deliverable; review the output against the source material.
npx skills add https://github.com/mohitmishra786/low-level-dev-skills --skill gpio-baremetalBefore you start
- Installation does not include a model subscription, API allowance or permission to access your files.
- Repository stars and installation counts describe activity, not an independent quality or security test.
Original skill document
Rendered from the source repository. Headings, examples, code, tables, links, and referenced images are preserved.
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
c
/* 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):
c
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
c
/* 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)
c
/* 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
| 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.
5. Agent usage
/gpio-baremetal Configure PA2 as USART2 TX alternate function on STM32F4Common Problems
| 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 |
Related Skills
skills/baremetal/mmio-and-bit-manipulation— BSRR/MODER masksskills/baremetal/peripherals-from-datasheet— RM pinout tablesskills/baremetal/uart-serial-baremetal— AF mux for serial
