gpio-baremetal
Skill290 starsChanged 7 months agoMITView on GitHub
Bare-metal GPIO skill for pin configuration and interrupts. Use when configuring GPIO modes, alternate functions, pull resistors, or EXTI interrupts on STM32/nRF/ESP32-class MCUs. Activates on queries about GPIO MODER, alternate function, pin interrupt, or LED/button bare-metal setup.
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The file
We split this skill into the rules it gives an agent
1 rule. About 0 are common, 1 is distinctive, and 0 are very specific to this project.
≈0
Common · estimate
Many files like this have a rule of this kind.
≈1
Distinctive · estimate
This author's own choices. Worth a look.
0
Very specific
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- Common
- Distinctive
- Very specific
- Distinctive: line 75
Always enable peripheral clock / power domain before pin config.
≈ “Common” is an estimate: at least 1 in 5 of the 350,495 skill files we read have a rule of the same kind, not the same words. “Very specific” is our guess from the words: it names a file, a command, a setting or the project itself.
Files
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
| 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
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