UART driver issue NUCLEO F411RE

[NicRoberts]

I'm trying to set up a simple UART debug just for transmission from the the NUCLEO board.

uart.c

#include "uart.h"

#define GPIOAEN			(1U<<0)
#define UART2EN			(1U<<17)

#define CR1_TE			(1U<<3)
#define CR1_UE			(1U<<13)
#define SR_TXE			(1U<<7)

#define SYS_FREQ		16000000
#define APB1_CLK		SYS_FREQ

#define UART_BAUDRATE	115200

static void uart2_set_baudrate(uint32_t periph_clk, uint32_t baudrate);
static uint16_t compute_uart_bd(uint32_t periph_clk, uint32_t baudrate);
static void uart2_write(int ch);


int __io_putchar(int ch)
{
	uart2_write(ch);
	return ch;
}

void uart2_tx_init(void)
{
	/*** Configure UART GPIO pin ***/
	/* Enable clock access to GPIOA */
	RCC->AHB1ENR |= GPIOAEN;

	/* Set PA2 mode to alternate function mode */
	GPIOA->MODER &=~ (1U<<4);
	GPIOA->MODER |= (1U<<5);

	/* Set PA2 alt function to UART tx (AF07) */
	GPIOA->AFR[0] |= (1U<<8);
	GPIOA->AFR[0] |= (1U<<9);
	GPIOA->AFR[0] |= (1U<<10);
	GPIOA->AFR[0] &=~ (1U<<11);

	/*** Configure the UART ***/
	/* Enable clock access to UART2 */
	RCC->AHB1ENR |= UART2EN;

	/* Configure baudrate */
	uart2_set_baudrate(APB1_CLK, UART_BAUDRATE);

	/* Configure transfer direction */
    USART2->CR1 = CR1_TE;

	/* Enable UART module */
    USART2->CR1 |= CR1_UE;
}

static void uart2_write(int ch)
{
	/* Ensure transmit data register empty */
	while(!(USART2->SR & SR_TXE)){}

	/* Write to the transmit data register */
	USART2->DR = (ch & 0xFF);
}


static void uart2_set_baudrate(uint32_t periph_clk, uint32_t baudrate)
{
	USART2->BRR = compute_uart_bd(periph_clk, baudrate);
}

static uint16_t compute_uart_bd(uint32_t periph_clk, uint32_t baudrate)
{
	return ((periph_clk + (baudrate / 2U)) / baudrate);
}

 uart.h

#ifndef __UART_H__
#define __UART_H__

#include "stm32f4xx.h"
#include <stdint.h>

void uart2_tx_init(void);

#endif

main.c

#include "stm32f4xx.h"
#include <stdio.h>
#include "uart.h"

static void psuedo_delay(int dly);

int main(void)
{
	/* Initialize UART2 */
	uart2_tx_init();

    while(1)
    {
    	printf("hi there!\n\r");
    	psuedo_delay(9000);
    }
}

static void psuedo_delay(int dly)
{
	for(int i = 0; i < dly; i++)
	{
             // DO NOTHING
	}
}

If I'm right then PA2 has been set up as a UART TX with a Baud rate of 115200 & this is connected to the USB on the board.

But when I open a TeraTerm window & connect to the board I get nothing just a blank terminal window. What am I missing here?

[Andrew Neil]

---

@NicRoberts wrote:

If I'm right then PA2 has been set up as a UART TX

---

You can confirm that in the board's User Manual:

https://www.st.com/resource/en/user_manual/um1724-stm32-nucleo64-boards-mb1136-stmicroelectronics.pdf

via: https://www.st.com/en/evaluation-tools/nucleo-f411re.html#documentation

You could also check the schematics:

via https://www.st.com/en/evaluation-tools/nucleo-f411re.html#cad-resources

---

@NicRoberts wrote:

with a Baud rate of 115200 

---

The baud rate can be whatever you like - it just has to match what you terminal is set to.

---

@NicRoberts wrote:

But when I open a TeraTerm window & connect to the board I get nothing 

---

Are you sure you're connecting to the correct COM port?

Do you have an Arduino shield (or any other hardware) connected which could interfere?

The manual describes various configuration options - has your board been modified?

Before adding the complications of printf, get it working with just direct UART output.

Have you tried one of the ready-made examples?

[NicRoberts]

OK so the board is set up correctly for use of USART2 over the ST-Link/USB connection, I have used this before with no issue with the board but just double checked & it all looks good.

No other hardware connected.

Baud rate on the board & the terminal match (115200),

COM5: STMicroelectronics STLink Virtual COM Port selected from Tera Term pull down

.....and nothing.....

[Andrew Neil]

Flow control set to 'None' ?

Have you tried one of the ready-made examples?

Do you have a scope to see if anything is actually coming out of the TX pin?

[NicRoberts]

Yes, flow control set to 'None'

Settings,

Baud : 115200

Data: 8 bit

Parity: none

Stop bits: 1

Flow control: none

Same config on TeraTerm

I'm trying to run some of the examples but the example selector keeps crashing CubeIDE

Got a simple HAL_UART_Transmit() code to work using printf() though, so I know the board is working now.

Still cant figure out why my bare metal implementation isn't working though.

[Andrew Neil]

---

@NicRoberts wrote:

Still cant figure out why my bare metal implementation isn't working though.

---

Step through the two examples; compare & contrast ...

Alternatively, start with the working HAL code, and pare that back to the minimum register operations ...

PS:

Or, of course, just use the HAL version as-is...

[Tesla DeLorean]

Are we sure APB1 is DIV2 and not DIV1 ?

Perhaps send 'U' patterns and scope the PA2 pin to confirm activity and bit-timing

If you're using bare-metal registers for efficiency, this is NOT efficient, and the compiler can't optimize / fold this because the registers are deemed volatile. So 4x load-store operations, when one load and one store would be the goal.

GPIOA->AFR[0] |= (1U<<8);
GPIOA->AFR[0] |= (1U<<9);
GPIOA->AFR[0] |= (1U<<10);
GPIOA->AFR[0] &=~ (1U<<11);

[NicRoberts]

Hi, 

I'm relatively new to STM32 so I'm doing everything long hand to get a better understanding but I get the sense in what you're are saying.

As for APB1, when I check against the auto-generated code the RCC initialiser uses DIV1. I thought I'd configured for DIV1?