Unable to on or off Green/BLUE LED STM32F429ZI - Nucleo board?

Question

I am trying to write a bare metal program to blink green led. In fact, I am unable to turn any LEDs on or off. This is an off-the-shelf board. The board name is NUCLEO F429ZI. Board Image

I have gone through the schematics and I am sure that the pin is PA5 i.e. Port A and pin number 5. However, the led isn't blinking at all. I can see that my code is loaded onto STM32 board using uVision IDE.

I have tried setting blue LED i.e. PB7 but that also didn't work at all.

void delayMs(int delay);

int main(void)
{
    //enable clock access to A
    RCC->AHB1ENR |= 1;  //enable GPIO A clock
    GPIOA->MODER |= 0x400; //       PA-5 01   0000 - PA0
    while(1)
    {
          GPIOA->ODR |= 0x20;
         //delay
          delayMs(100);
          GPIOA->ODR &=~ 0x20;
          delayMs(100);
    }

}

void delayMs(int delay)
{
    int i = 0;
    for(; delay >0; delay--)
    {
     for(i=0; i<3195; i++)
        {
        }
    }
}

The green LED in the STM32F429ZI should blink.

Next, I tried turning on the blue LED that is also not working. As per my understanding by looking at schematics - PB7 should be turned on for blue LED. But this is also not working.

#include "stm32f4xx.h"
int main(void)
{
    RCC->AHB1ENR |= 1;
    // ob 01 00 00 00 00 00 00 00 // PB7
    GPIOB->MODER = 0x4000;
    for(;;)
    {
        GPIOB->ODR = 0x80;
    }
}

Answer 1

Rather unhelpfully the Nucleo F429ZI UM1974 user manual download link at https://www.st.com/en/evaluation-tools/nucleo-f429zi.html#resource appears to be broken (at time of writing), but I have found a copy elsewhere, and the pin assignments of the three user LEDs is described thus:

The schematic suggests that the factory state of solder-bridges SB120 and SB119 are set for LD1 on PB0 rather then PA5. The problem with your attempt to set LD2 (blue) is that you did not enable GPIOB in the RCC - it enables GPIOA as in the LD1(green) attempt.

Another issue is that your setting of GPIO MODER assumes that the reset state for the port is zero. That is not the case (although it is for the specific pins in question - so you "get away with it" in this case):

It is a good idea to define all the port/pin specific constants in one place so you can switch or add outputs easily and with less chance of error:

#define LED_PORT              GPIOB
#define LED_PORT_RCC_EN       0x2u 
#define GPIO_MODE_MASK       ~0x3u
#define GPIO_MODE_OUTPUT      0x1u

#define GREEN_LED_PIN         0u
#define BLUE_LED_PIN          7u
#define RED_LED_PIN           14u
#define FLASH_LED             GREEN_LED_PIN

int main(void)
{
    RCC->AHB1ENR |= LED_PORT_RCC_EN ;
    LED_PORT->MODER &= GPIO_MODE_MASK << (FLASH_LED << 1) ;
    LED_PORT->MODER |= GPIO_MODE_OUTPUT << (FLASH_LED << 1) ;

    for(;;)
    {
          LED_PORT->ODR |= 0x1 << FLASH_LED ;
          delayMs( 100 ) ;
          LED_PORT->ODR &= ~(0x1 << FLASH_LED) ;
          delayMs( 100 ) ;
    }

    return 0 ;
}

Your delay function is seriously flawed, and likely to be optimised out to "do nothing". Your loop counter needs to be declared volatile to avoid being optimised out. If that happens, the indicator will not visibly blink but will be pulsed at a very high frequency and be on but not at full brightness.

The following will prevent the loops being optimised out.

void delayMs( unsigned delay )
{
    for( volatile unsigned d = delay; d > 0; d--)
    {
        for( volatile int i = 0; i < 3195; i++ )
        {
        }
    }
}

However it is a 180MHz part; if you are running it at full-speed 3195 iterations it will probably not take 1ms. More like a few tens of microseconds. Even if running at the start-up HSI frequency of 16MHz, it is likely to of the order of a few 100s of microseconds, and will in any case vary with optimisation settings and time spent in any interrupt handlers running. Much better to use the Cortex-M SYSTICK counter as follows:

static volatile uint32_t ms_tick = 0 ;

void SysTick_Init(void) 
{
    SysTick_Config( SystemCoreClock / 1000 ) ;  
}

void SysTick_Handler(void)
{
    ms_tick++;
}

void delayMs( uint32_t delay)
{
    uint32_t start_tick = ms_tick ;
    while( (ms_tick - start_tick) < delay );
}

Then the delay will be accurate regardless of the clock speed you run your processor at or interrupt load.

Answer 2

You should not modify ODR directly as it does a read/write on the entire port. Instead you should use the BSRR register where you can affect one bit only. Note that some STM32 part uses a single 32-bit BSRR register to set and clear the bits (one operation is shifted 16 bit left) whereas others use two 16-bit registers so consult the reference manual or header file for details.

Your MODER setting is incorrect. You need to clear the 2 bits for PA5 first, before OR'ing 01 in, e.g.

GOPIOA->MODER &= ~0b1100000000;
GPIOA->MODER |= 0b0100000000;

Answer 3

This is complete solution for Nucleo 144 - STM32F429ZI.

#include "stm32f4xx.h"

#define LED_PORT              GPIOB
#define LED_PORT_RCC_EN       0x2u 
#define GPIO_MODE_MASK       ~0x3u
#define GPIO_MODE_OUTPUT      0x1u

#define GREEN_LED_PIN         0u
#define BLUE_LED_PIN          7u
#define RED_LED_PIN           14u
#define FLASH_LED             BLUE_LED_PIN


void delayMs( unsigned delay );

int main(void)
{
    RCC->AHB1ENR |= LED_PORT_RCC_EN ; // enable for PORT B
    //LED_PORT->MODER &= GPIO_MODE_MASK << FLASH_LED ;
    //LED_PORT->MODER |= GPIO_MODE_OUTPUT << FLASH_LED ;
      GPIOB->MODER |= 0x4000;  // blue LED PB7
      GPIOB->MODER |= 0x1;  // green LED PB0
      GPIOB->ODR |= 0x1; // green LED ODR
      GPIOB->MODER |=  0x1 << 28; // red LED PB14
      GPIOB->ODR |= 0x1 <<14; // RED LED ODR
      //GPIOB->BSRR |= 0x4000; // 7th pin 
    // connected to pull up resistor -- when we press button , it goes low
        //B1 user button is connected to PC13 - i.e. blue button
      // Enable clock to PC13 i.e. Port C
      RCC->AHB1ENR |=  0x1 << 2;
      //GPIOC->MODER |=     //Input mode PC13- 13th pin 0
       // by default pins are input only
      GPIOC->MODER |=  0;
    for(;;)
    {
               // pressed blue button
               if( (GPIOC->IDR & (1<<13)) ) // PC13
                 {
                      LED_PORT->ODR |= 0x1 << FLASH_LED ;

                 }
                 else
                 {
            LED_PORT->ODR &= ~(0x1 << FLASH_LED) ;

                 }
    }

    return 0 ;
}

void delayMs( unsigned delay )
{
    for( volatile unsigned d = delay; d > 0; d--)
    {
        for( volatile int i = 0; i < 3195; i++ )
        {
        }
    }
}