STM32 HAL_UART_Transmit_IT never returns - embedded

Question

I have created a project using cube mx and want to use the uart4 tx and rx to send and receive bytes in interrupt mode.
I have :
uint8_t buffer[] = "test\r\n";
if(HAL_UART_Transmit_IT(&huart4, (uint8_t*)buffer, strlen(buffer))!= HAL_OK)
{
}
The uart initialisation is
static void MX_UART4_Init(void)
{
huart4.Instance = UART4;
huart4.Init.BaudRate = 9600;
huart4.Init.WordLength = UART_WORDLENGTH_8B;
huart4.Init.StopBits = UART_STOPBITS_1;
huart4.Init.Parity = UART_PARITY_NONE;
huart4.Init.Mode = UART_MODE_TX_RX;
huart4.Init.HwFlowCtl = UART_HWCONTROL_NONE;
huart4.Init.OverSampling = UART_OVERSAMPLING_16;
huart4.Init.OneBitSampling = UART_ONE_BIT_SAMPLE_DISABLE;
huart4.AdvancedInit.AdvFeatureInit = UART_ADVFEATURE_NO_INIT;
if (HAL_UART_Init(&huart4) != HAL_OK)
{
_Error_Handler(__FILE__, __LINE__);
}
}
The call to Transmit never returns and just sits there.
In the msp file I have
HAL_NVIC_SetPriority(UART4_IRQn, 0, 0);
HAL_NVIC_EnableIRQ(UART4_IRQn);
and have in the it file
void UART4_IRQHandler(void)
{
/* USER CODE BEGIN UART4_IRQn 0 */
/* USER CODE END UART4_IRQn 0 */
HAL_UART_IRQHandler(&huart4);
/* USER CODE BEGIN UART4_IRQn 1 */
/* USER CODE END UART4_IRQn 1 */
}
what am I missing?

Answer 1

the problem is related to uint8_t buffer[] = "test\r\n";
the right side is char and the left side is uint8. So, you must do as follows
char buffer[] = "test\r\n";
if(HAL_UART_Transmit_IT(&huart4, (char*)buffer, strlen(buffer))!= HAL_OK)
{
}
or you can do this (use sizeof for int8_t not strlen)
unit8_t buffer[] = "test\r\n";
if(HAL_UART_Transmit_IT(&huart4, (uint8_t*)buffer, sizeof(buffer))!= HAL_OK)
{
}
please add "string.h" and in the first line of you code

Answer 2

Adding a delay too allow the data to be sent fixed this problem. HAL_Delay(100)