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DZado.2
Visitor II
December 17, 2024
Solved

Help to use PA15 as GPIO Output on NUCLEO-L476RG

  • December 17, 2024
  • 4 replies
  • 1446 views

Hi,

 I am a newbie with STM32. I need help.

I want to configure that PA15 pin (which by default is used as JTDI), as a GPIO output.

I've added the following two lines to the beginning of the generated code of MX_GPIO_Init():

LL_GPIO_SetAFPin_8_15(GPIOA,LL_GPIO_PIN_15,LL_GPIO_AF_5);

LL_GPIO_SetPinMode(GPIOA,LL_GPIO_PIN_15,LL_GPIO_MODE_OUTPUT);

But it does not work. I connected a LED and tried to change the state of the pin high and low,

but it did not work.

I appreciate if someone help me to figure out what I am missing.

Thanks

    This topic has been closed for replies.
    Best answer by Karl Yamashita
    @DZado.2 wrote:

    I did two changes:

    1) I removed the lines (as gbm proposed):

    //LL_GPIO_SetAFPin_8_15(GPIOA,LL_GPIO_PIN_15,LL_GPIO_AF_5);

    //LL_GPIO_SetPinMode(GPIOA,LL_GPIO_PIN_15,LL_GPIO_MODE_OUTPUT);

    1) And I added 

    LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOA);

    in addition to

    __HAL_RCC_GPIOA_CLK_ENABLE();

     

    Now it is working. I have no clue why.

    If I remove LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOA), it does not work.

    Would you please explain why?

     

     

    I'm not sure? The LL and HAL are setting the same register/bit, though the LL is static inline

    Look at the disassembly to see what each is doing.

    // HAL
#define __HAL_RCC_GPIOA_CLK_ENABLE() do { \
 __IO uint32_t tmpreg; \
 SET_BIT(RCC->AHB2ENR, RCC_AHB2ENR_GPIOAEN); \
 /* Delay after an RCC peripheral clock enabling */ \
 tmpreg = READ_BIT(RCC->AHB2ENR, RCC_AHB2ENR_GPIOAEN); \
 UNUSED(tmpreg); \
 } while(0)





// LL
#define LL_AHB2_GRP1_PERIPH_GPIOA RCC_AHB2ENR_GPIOAEN

LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOA);

__STATIC_INLINE void LL_AHB2_GRP1_EnableClock(uint32_t Periphs)
{
 __IO uint32_t tmpreg;
 SET_BIT(RCC->AHB2ENR, Periphs);
 /* Delay after an RCC peripheral clock enabling */
 tmpreg = READ_BIT(RCC->AHB2ENR, Periphs);
 (void)tmpreg;
}

     

    4 replies

    G
    gbm
    Graduate
    December 17, 2024

    Is the GPIOA enabled in RCC? Setting AF is not needed, it's enough to set the output mode. You may do the same via CubeMX.

    D
    DZado.2Author
    Visitor II
    December 17, 2024

    I did enable RCC by this API: __HAL_RCC_GPIOA_CLK_ENABLE();

    It does the job. Doesn't it?

    K
    Karl Yamashita
    Graduate II
    December 17, 2024

    Yes, either way should set the bit.

    Which L4 are you using?

    Are you using a Nucleo board or a custom board?

    K
    Karl Yamashita
    Graduate II
    December 17, 2024

    You haven't indicated if you enable the GPIO clock?

     

    LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOA);

     

    KarlYamashita_0-1734466006067.png

     

    D
    DZado.2Author
    Visitor II
    December 17, 2024

    Thanks for your reply.

    I did by the HAL function: __HAL_RCC_GPIOA_CLK_ENABLE();

    I am not sure if I can mix up the LL and the HAL functions together :)

    K
    Karl Yamashita
    Graduate II
    December 17, 2024

    It seems you've added code manually. So have any peripherals been enabled that could be using that same pin? 

    D
    DZado.2Author
    Visitor II
    December 26, 2024

    Thanks a lot Karl and gbm.

    You solved my issue.

    Happy new year

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