How to enable UART for STM32 Nucleo F429ZI? - embedded

Question

I am trying to enable UART for STM32 Nucleo - F429ZI.
I have gone through user manual and it says by default USART 3 can be configured for virtual com port purpose. Here is my code. I can see that USART 3 has pins D8 and D9. Here is my code. What am I doing wrong here, I don't see prints on my com port.
Data sheet refered - https://www.st.com/resource/en/data_brief/nucleo-f429zi.pdf
https://www.st.com/resource/en/user_manual/dm00244518-stm32-nucleo-144-boards-stmicroelectronics.pdf
//test print msg
char usr_msg[256];
//Ends
void printmsg(char *msg)
{
for(uint32_t i = 0; i < strlen(msg); i++)
{
while(USART_GetFlagStatus(USART3, USART_FLAG_TXE) != SET);
USART_SendData(USART3, msg[i]);
}
}
static void prvSetupUart(void)
{
GPIO_InitTypeDef gpio_uart_pins;
USART_InitTypeDef uart3_init;
//GPIO D is connected to AHB1 bus.
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);
// Enable the UART 3 peripheral clock -- connected to APB1 bus.
RCC_APB1PeriphClockCmd(RCC_APB1Periph_USART3, ENABLE);
// zero the local variable
memset(&gpio_uart_pins,0,sizeof(gpio_uart_pins));
memset(&uart3_init,0,sizeof(uart3_init));
// GPIO port D - pin 8 like TX
// GPIO port D - ping 9 like RX
gpio_uart_pins.GPIO_Pin = GPIO_Pin_8 | GPIO_Pin_9;
gpio_uart_pins.GPIO_Mode = GPIO_Mode_AF; //AF - Alternate function i.e. TX and RX.
gpio_uart_pins.GPIO_PuPd = GPIO_PuPd_UP; //Pull up so that we see some default voltage.
GPIO_Init(GPIOD, &gpio_uart_pins);
uart3_init.USART_BaudRate = 115200;
uart3_init.USART_HardwareFlowControl = USART_HardwareFlowControl_None;
uart3_init.USART_Mode = USART_Mode_Tx | USART_Mode_Rx;
uart3_init.USART_Parity = USART_Parity_No;
uart3_init.USART_StopBits = USART_StopBits_1;
uart3_init.USART_WordLength = USART_WordLength_8b;
USART_Init(USART3,&uart3_init);
//Enable USART 3 peripheral.
USART_Cmd(USART3, ENABLE);
}
int main(void)
{
//Step number 1 - DeInit the RCC - Reset Control Clock so that we don't use Pre-scaler or PLL.
// Basically, we want to use lower speed.
RCC_DeInit();
// update the System Core Clock
//Step number 2 -- Update the clock to use the default clock.
SystemCoreClockUpdate();
prvSetupUart();
sprintf(usr_msg, "This is Hello World\r\\n");
printmsg(usr_msg);
for(;;);
}

Answer 1

you forgot to set what AF mode to be used (there are possible 16 AF modes for every pin). At the moment AF registers are set to the 0 and it is wrong. You need to make it 7.
How can it be archived using the SPL library (depreciated and not supported anymore) I do not know.
Here is the register version
#define GPIO_AFRL_AFRL0_Msk (GPIO_AFRL_AFRL0_0 | GPIO_AFRL_AFRL0_1 | GPIO_AFRL_AFRL0_2 | GPIO_AFRL_AFRL0_3)
void GPIO_SetAF(GPIO_TypeDef *gpio, unsigned pin, unsigned AF)
{
volatile uint32_t *AFreg = &gpio -> AFR[pin >= 8];
if(AF <= 15)
{
if(pin > 7) pin -= 8;
*AFreg &= ~(GPIO_AFRL_AFRL0_Msk << (4 * pin));
*AFreg |= (AF << (4 * pin));
}
}