UART例程

你好，我使用的是DA14531 Development Kit-USB 开发板，在运行uart的官方例程时，

void uart_receive_blocking_example(uart_t* uart)
{
    printf_string(uart, "\n\r\n\r****************************************\n\r");
    if (uart == UART1)
    {
        printf_string(uart, "* UART1 Receive Blocking example *\n\r");
    }
    else
    {
        printf_string(uart, "* UART2 Receive Blocking example *\n\r");
    }
    printf_string(uart, "****************************************\n\r\n\r");

    printf_string(uart, "Type 5 characters.\r\n");

    uart_receive(uart, (uint8_t *)buffer, READ_CHAR_COUNT, UART_OP_BLOCKING);

    buffer[READ_CHAR_COUNT] = 0; // make it a null terminated string

    printf_string(uart, "You typed the following characters:\r\n");
    printf_string(uart, buffer);
    printf_string(uart, "\r\n");

    printf_string(uart, "****************************************\n\r\n\r");
}

在程序跑到  uart_receive(uart, (uint8_t *)buffer, READ_CHAR_COUNT, UART_OP_BLOCKING);时，运行不下去，此时应该输入5个字符，通过串口助手发送5个字符也不行，请问是哪里出现了问题。