LED not turning on on Nucleo-L031K6 with direct GPIO register access (bare-metal)

[kuhicop]

I am trying to turn on the LD3 LED (connected to PB3) on the NUCLEO-L031K6 board using direct register access without libraries, but it is not working. The LED does not turn on. I have configured the pin control register, enabled the GPIOB clock, and set pin PB3 as output, but the LED still does not light up.

Here is the code I am using:

// NUCLEO-L031K6
#define PERIPH_BASE (0x40000000UL)

#define AHB_OFFSET (0x00020000UL)
#define AHB_BASE (PERIPH_BASE + AHB_OFFSET)

#define IO_OFFSET (0x10000000UL)
#define IOPORT_BASE (PERIPH_BASE + IO_OFFSET)

#define GPIOB_OFFSET (0x0400UL)
#define GPIOB_BASE (IOPORT_BASE + GPIOB_OFFSET)

#define RCC_OFFSET (0x00021000UL)
#define RCC_BASE (AHB_BASE + RCC_OFFSET)

#define RCC_IOPENR_OFFSET (0x2CUL)
#define RCC_IOPENR (*(volatile unsigned int *)(RCC_BASE + RCC_IOPENR_OFFSET))

#define GPIOPBEN (1U<<1)

#define GPIOBMODER_OFFSET (0x00UL)
#define GPIO_MODER (*(volatile unsigned int *)(GPIOB_BASE + GPIOBMODER_OFFSET))

#define GPIO_ODR_OFFSET (0x14UL)
#define GPIO_ODR (*(volatile unsigned int *)(GPIOB_BASE + GPIO_ODR_OFFSET))

#define GPIOB_PIN3 (1U<<3) // LD3 user LED

int main() {
 // Enable GPIOB clock
 RCC_IOPENR |= GPIOPBEN;

 // Set GPIOB pin 3 as output
 GPIO_MODER |= (1U<<6);
 GPIO_MODER &=~ (1U<<7);
 GPIO_ODR |= GPIOB_PIN3; // Turn on LED (set PB3 to HIGH)

 while (1) {
 }
}

Details:

• Clock enabling: I am enabling the clock for GPIOB with RCC_IOPENR |= GPIOPBEN.
• Pin configuration as output: I am setting PB3 as output by modifying the MODER register (clearing and setting bits 6 and 7 of GPIOB_MODER).
• Turn on the LED: I am writing a 1 to the ODR register to set PB3 to HIGH and turn on the LED.

However, the LED is not turning on. Is there something I'm missing in the configuration?

What I've tried:

• I have tried with and without the code that sets GPIOB as output.
• I've also checked that there are no obvious hardware issues.

What else can I check or correct to turn on the LED on this board?

[MHank.1]

First thing that catches my eye is in this code;

 

 // Set GPIOB pin 3 as output
 GPIO_MODER |= (1U<<6);
 GPIO_MODER &=~ (1U<<7);
 GPIO_ODR |= GPIOB_PIN3; // Turn on LED (set PB3 to HIGH)

 while (1) {
 }

 

First clear both bits then set the correct one.

 

[gbm]

1. Use ST-supplied headers to avoid looking for errors in your non-standard stuff.

2. Use debugger to single-step through your code and examine GPIOB registers.

 

[kuhicop]

I'm learning bare-metal without headers, that's my purpose of understanding everything from scratch

[gbm]

No, you are learning bare metal with non-standard, non portable, incorrect headers inserted into .c source files. Not really a good idea.

[waclawek.jan]

RCC offset to AHB area beginning is not 0x0002'1000 but 0x0000'1000.

Using the CMSIS-mandated device header - as @gbm suggested above - avoids this sort of errors.

JW

[kuhicop]

I see as 0x0002'1000 in the reference manual

[waclawek.jan]

No, 0x0002'1000 is offset to 0x4000'0000, not offset to AHB area beggining, which already has an offset of 0x0002'0000.

#define PERIPH_BASE (0x40000000UL)

#define AHB_OFFSET (0x00020000UL)
#define AHB_BASE (PERIPH_BASE + AHB_OFFSET)
------> AHB_BASE == 0x4002'0000
#define RCC_OFFSET (0x00021000UL)
#define RCC_BASE (AHB_BASE + RCC_OFFSET)
-----> RCC_BASE == 0x4004'1000, which is incorrect

 

JW