Help to use PA15 as GPIO Output on NUCLEO-L476RG

[DZado.2]

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

[gbm]

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.

[Karl Yamashita]

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

LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOA);

[DZado.2]

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 :)

[DZado.2]

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

It does the job. Doesn't it?

[Karl Yamashita]

Yes, either way should set the bit.

Which L4 are you using?

Are you using a Nucleo board or a custom board?

[DZado.2]

I am using  NUCLEO-L476RG

(not a custom board)

[DZado.2]

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?

[Karl Yamashita]

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

[Karl Yamashita · Accepted solution]

---

@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;
}