吐槽：28027的SPI速度太慢了！

Internal clock prescalers must be adjusted such that the SPI clock speed is limited to the following SPI clock rate:
Master mode transmit 15-MHz MAX, master mode receive 10-MHz MAX
Slave mode transmit 10-MHz MAX, slave mode receive 10-MHz MAX.

mangui zhang：综合最好时钟考虑SPI接收缓存解码处理加上CPU干其他的事
这速度也就差不多了太高也意义不大了