printf causes terminal to stay just empty.

[stmax]

Hey. I tried to setup `printf` using the following forum post. I am using the `NUCLEO-L4A6ZG`.

Here what I've tried so far. I connected the `USART2` to the Pins `PA2` (RX) and `PA3` (TX):

(By default LPUART1 was configured and connected to PG7/8, since the forum post used USART2 I used it as well.)

After the configuration was saved, and the code generated, I used the code from the previous mentioned forum post. Here a shorter and with comments removed version:

/* Includes ------------------------------------------------------------------*/
#include "main.h"
#include "stdio.h"

// ...

/* Private variables ---------------------------------------------------------*/
UART_HandleTypeDef huart2;

// ...

/* Private function prototypes -----------------------------------------------*/
void SystemClock_Config(void);
static void MX_GPIO_Init(void);
static void MX_USB_OTG_FS_PCD_Init(void);
static void MX_USART2_UART_Init(void);

/* USER CODE BEGIN PFP */
#define PUTCHAR_PROTOTYPE int __io_putchar(int ch)
/* USER CODE END PFP */

// ...
int main(void)
{
    HAL_Init();

    SystemClock_Config();

    MX_GPIO_Init();
    MX_USB_OTG_FS_PCD_Init();
    MX_USART2_UART_Init();

    while (1)
    {
        /* USER CODE END WHILE */
        printf("Hello, World!\n\r");
	    HAL_Delay(1000);
        /* USER CODE BEGIN 3 */
    }
}

// ...

static void MX_USART2_UART_Init(void)
{
    huart2.Instance = USART2;
    huart2.Init.BaudRate = 115200;
    huart2.Init.WordLength = UART_WORDLENGTH_7B;
    huart2.Init.StopBits = UART_STOPBITS_1;
    huart2.Init.Parity = UART_PARITY_NONE;
    huart2.Init.Mode = UART_MODE_TX_RX;
    huart2.Init.HwFlowCtl = UART_HWCONTROL_NONE;
    huart2.Init.OverSampling = UART_OVERSAMPLING_16;
    huart2.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
    huart2.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
    if (HAL_UART_Init(&huart2) != HAL_OK)
    {
        Error_Handler();
    }
}

// ...

/* USER CODE BEGIN 4 */
PUTCHAR_PROTOTYPE {
	HAL_UART_Transmit(&huart2, (uint8_t *)&ch, 1, 0xFFFF);
	return ch;
}
/* USER CODE END 4 */

Then I build it, created the Debug-Profile and ran/resumed it via the Debug-Mode.

I wanted to connect via PuTTY. I turned Flow Control off, and set the data bits to 7. Here are the settings:

When I select open I can connect, but the terminal stays just empty.

I not sure where the problem is. I would be very grateful if someone could help me.

[Andrew Neil]

---

@Andrew Neil wrote:

---

These things are also documented in the User Manual, UM2179:

---

Although UM2179 omits this from Fig 3

🙄

See separate post:

https://community.st.com/t5/stm32-mcus-boards-and-hardware/um2179-doesn-t-show-the-vcp-uart-connection/m-p/644955#M17437

[stmax]

Sorry if i need to ask again. But does the the STLK_RX/TX refer to those two pins?

I tried to connect RX/TX to them like this. But it didn't work either:

I'm sorry for those dumb questions. Currently feeling totally overwhelmed by all the schematics and documentation. If there is a more straight forward way to configure printf i would of course do use it too.

[SofLit]

Remove the ones crossed.

You have to use the one in rectangle and you have to connect UART2_Tx/UART2_Rx from CNx connectors

[SofLit]

@stmax  please keep my answer marked as solution as I've already answered your question.

Now you ask a new question so you need either to open a new thread or keep this discussion but the original question was answered.

Thank you for your understanding.

[stmax]

Okay now It works. Thank you so much for your time and patience!

[Andrew Neil]

@SofLit This is a common issue that comes up quite a lot.

As well as clarifying the VCP UART connection diagram (as already mentioned), I think the ST-Link section should specifically state what UART the VCP connects to, and cross-reference to the section with the details:

Perhaps also something could be added  on "how to use a different UART" ... ?

[SofLit]

I think it's something managed in transversal. Each board has it's own UART (sometimes USART1, others USART3, others LPUART1 etc ..). So I think it's not easy to manage in the documentation.

[Andrew Neil]

Fair, although the UM2179 here does specifically refer to LPUART1:

There should at least be a cross-reference from the ST-Link section to this section (or its equivalent).

[SofLit]

Yes this is a specific section for this board while the other (I think) is a generic paragraph that implies all Nucleo boards. 

Does this kind of specific paragraph available in all UM?: