Why Debug (printf) viewer has no output in Keil?

Hi ,

I'm trying to print something via "ITM_SendChar();"  in the Debug (printf) Viewer of Keil. But it seems no work for me.

Environment:  KEIL v5.17 + STM32L475VE + ST-LINK V2-1

Trace settings:

Code in main.c:

void main(void)
{
    //SYSCLK = HSE / PLLM * PLLN / PLLR
    //SYSCLK = 8M / 1 * 20 /2 = 80M
    SystemClock_Config();
    while(1) ITM_SendChar('A');
}

Observed things:

1. There is no prints in the debug (printf) viewer(see pictures)

2. There is "Trace: no synchronization" in the status bar during the running.(see pictures)

Any ideas ?

Thanks in advance.