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.

[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

[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]

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

[TDK]

Is translating addresses in the RM into pointers really helping you learn anything here? The learning comes with manipulating registers and understanding how they work, not with the addresses themselves. Use the standard CMSIS headers. You could have spent time learning instead of tracking down a typo here.

[kuhicop]

I'm following a course, the first lessons are without headers, I won't be touching CMSIS until the next lessons.

I said learning from scratch. And to me from scratch means from scratch. Using an empty project without any headers or anything. That's what I understand from scratch, where you're using NOTHING BUT AN EMPTY PROJECT.

I don't know the reason right now as I'm completely new to this, but the course is structured like that for some reason, and I don't think I'm loosing time understanding how everything is build from A to Z. If I use someone else libraries, headers or any piece of code then I already skipped knowledge.

That's my opinion :)