USART not working on STM32L475 after setup - stm32

Question

I work with a demo board B-L475E-IOT01A. On CN3 connector - pin1 - PA1-RX, pin2 - PA0-TX. So I configure for UART4.
#define UART4_PORT GPIOA
#define UART4_TX_PIN LL_GPIO_PIN_0
#define UART4_RX_PIN LL_GPIO_PIN_1
int USART_Setup(USART_TypeDef *USARTx, uint32_t baud_rate)
{
LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOA);
LL_APB2_GRP1_EnableClock(LL_APB2_GRP1_PERIPH_SYSCFG);
if (USARTx == UART4)
{
irq_num = UART4_IRQn;
/* Configure Tx Pin as : Alternate function, High Speed, Push pull, Pull up */
LL_GPIO_SetPinMode(UART4_PORT, UART4_TX_PIN, LL_GPIO_MODE_ALTERNATE);
LL_GPIO_SetAFPin_8_15(UART4_PORT, UART4_TX_PIN, LL_GPIO_AF_8);
LL_GPIO_SetPinSpeed(UART4_PORT, UART4_TX_PIN, LL_GPIO_SPEED_FREQ_HIGH);
LL_GPIO_SetPinOutputType(UART4_PORT, UART4_TX_PIN, LL_GPIO_OUTPUT_PUSHPULL);
LL_GPIO_SetPinPull(UART4_PORT, UART4_TX_PIN, LL_GPIO_PULL_UP);
/* Configure Rx Pin as : Alternate function, High Speed, Push pull, Pull up */
LL_GPIO_SetPinMode(UART4_PORT, UART4_RX_PIN, LL_GPIO_MODE_ALTERNATE);
LL_GPIO_SetAFPin_8_15(UART4_PORT, UART4_RX_PIN, LL_GPIO_AF_8);
LL_GPIO_SetPinSpeed(UART4_PORT, UART4_RX_PIN, LL_GPIO_SPEED_FREQ_HIGH);
LL_GPIO_SetPinOutputType(UART4_PORT, UART4_RX_PIN, LL_GPIO_OUTPUT_PUSHPULL);
LL_GPIO_SetPinPull(UART4_PORT, UART4_RX_PIN, LL_GPIO_PULL_UP);
LL_APB1_GRP1_EnableClock(LL_APB1_GRP1_PERIPH_UART4);
LL_RCC_SetUSARTClockSource(LL_RCC_UART4_CLKSOURCE_PCLK1);
}
NVIC_SetPriority(irq_num, 0);
NVIC_EnableIRQ(irq_num);
/* TX/RX direction */
LL_USART_SetTransferDirection(USARTx, LL_USART_DIRECTION_TX_RX);
/* 8 data bit, 1 start bit, 1 stop bit, no parity */
LL_USART_ConfigCharacter(USARTx, LL_USART_DATAWIDTH_8B, LL_USART_PARITY_NONE, LL_USART_STOPBITS_1);
LL_USART_SetBaudRate(USARTx, SystemCoreClock, LL_USART_OVERSAMPLING_16, baud_rate);
LL_USART_Enable(USARTx);
//enable RX buffer not empty interrupt
USARTx->CR1 |= USART_CR1_RXNEIE;
/* Polling USART initialisation */
while((!(LL_USART_IsActiveFlag_TEACK(USARTx))) || (!(LL_USART_IsActiveFlag_REACK(USARTx))))
{
timeout++;
if (timeout > 1000000)
{
return USART_ERROR;
}
}
return USART_OK;
}
I go line by line in the debugger and it seems to be OK. However when I connect to a terminal with TTL-USB convertor there is no transmission and no reception. Both LEDs TX/RX on TTL-USB convertor are on. TTL-USB convertor tested on other boards and works OK. Do I miss something?

Answer 1

first I enable port clocks
LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOA);
LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOB);
LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOC);
LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOD);
LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOE);
LL_AHB2_GRP1_EnableClock(LL_AHB2_GRP1_PERIPH_GPIOH);
LL_APB2_GRP1_EnableClock(LL_APB2_GRP1_PERIPH_SYSCFG);
after that I see
GPIOA->AFRL - 0x00000000
GPIOA->AFRH - 0x00000000
Then after
LL_GPIO_SetAFPin_8_15(UART4_PORT, UART4_TX_PIN, LL_GPIO_AF_8);
LL_GPIO_SetAFPin_8_15(UART4_PORT, UART4_RX_PIN, LL_GPIO_AF_8);
it stays all zeroes.
GPIOA->AFRL - 0x00000000
GPIOA->AFRH - 0x00000000