RTOS/AM4379: UART3 read issue

Part Number: AM4379

Tool/software: TI-RTOS

Hi,

pdk_am437x_1_0_6
PRU-ICSS-HSR-PRP-DAN_01.00.02.00
bios_6_46_04_53
CCS7


Please look to my example code:

    UART_Params_init(&params);
    params.parityType = UART_PAR_ODD;
    params.readEcho = UART_ECHO_OFF;
    params.readTimeout = 1000;
    params.readReturnMode = UART_RETURN_FULL;
    params.readDataMode = UART_DATA_BINARY;
    uartGPS_handle = UART_open(USART_GPS_INST, &params);
    if(uartGPS_handle == NULL){
        UART_printf("Can't open UART GPS\n\r");
        return;
    }

    while(1){
        memset(buf, 0, sizeof(buf));
        if(UART_read(uartGPS_handle, buf, 10)){
            UART_printf("%s\n", buf);
        }
        else{
            UART_printf("time OUT\n");
        }
    }

Issue symptom:
I constantly getting "time OUT". Before I had UART params set to BIOS_WAIT_FOREVER and task stuck on UART_read.

If I put hardware break point before UART_read, the data appears and are printed to console.

What did I miss? Strange is that code work if I stop CPU for short time in while....

Best Regards, Mare