这个例子显示了如何配置SSI0为TI spi模式。该代码将对主机发送三个字符，然后轮询接收FIFO，直到3个字符在主Rx接收buff空间。-This example shows how to configure the SSI0 as TI Master.　The code will send three characters on the master Tx then poll the receive FIFO until 3 characters are received on the master Rx.