Hi,

As far as I understand the problem comes with the msg.
If it stores only 1 character as in your book example it works fine but if I change the message then I get strange output like this

Welcome to the Nucleo management console
Select the option you are interested in:
.1. Toggle LD2 LED
.2. Read USER BUTTON status
.3. Clear screen and print this message
Selection: > You sele….Ë…∫…˛..
Selection: > Yo….ˇˇ….Ë…….˛..
Selection: > Yo….ˇˇ….Ë…….˛P.
Selection: > You sele….Ë…….˛..
Selection: > Yo..˘ˇˇˇˇ…Ë……….
Selection: >

uint8_t processUserInput(uint8_t opt) {
char msg[30];

if(!(opt >= 1 && opt <= 3))
return 0;

//sprintf(msg, “%d”, opt);
sprintf(msg, “You selected option %d\r\n”, opt);

UART_Transmit(&huart2, (uint8_t*)msg, strlen(msg));

switch(opt) {
case 1:
HAL_GPIO_TogglePin(GPIOA, GPIO_PIN_5);
break;
case 2:
sprintf(msg, “\r\nUSER BUTTON status: %s”, HAL_GPIO_ReadPin(GPIOC, GPIO_PIN_13) == GPIO_PIN_RESET ? “PRESSED” : “RELEASED”);

As far as I understand if the UART is not HAL_BUZY the UART_Transmit() directly the first char while if HAL_BUZY it stores the string in the txBuf.
After that point I am not sure…
What is going on with the next call to

void HAL_UART_TxCpltCallback(UART_HandleTypeDef *huart){
//trace_puts(“UART Tx IT Complete\n”);
if(RingBuffer_GetDataLength(&txBuf) > 0){
RingBuffer_Read(&txBuf, &txData, 1);
HAL_UART_Transmit_IT(huart, &txData, 1);
}
}

Could you clarify this to help?

Thank you so much

As far as understand is related to msg array being out of scope when using interlocks.
If you move the msg[30] to a global scope then it works fine for me.
Note: I was also getting wrong info from the debugger not flashing the firmware on restart.