翻出来一块扩展板，好久以前一个树莓派爱好者送的。找了找资料，简单安装一下就跑起来了。


https://raspberrypiwiki.com/index.php/Raspberry_Pi_DIDO_Board


树莓派 Python 库设置 SPI 频率的方法（不修改一下不能识别到 SPI 设备）
https://raspberrypi.stackexchange.com/questions/67028/piface-digital-2-and-raspberry-pi-3?rq=1

Edit file /usr/local/lib/python3.5/dist-packages/pifacecommon/spi.py

加上 `speed_hz=ctypes.c_uint32(100000) `这行。

```
create the spi transfer struct
transfer = spi_ioc_transfer(
tx_buf=ctypes.addressof(wbuffer),
rx_buf=ctypes.addressof(rbuffer),
len=ctypes.sizeof(wbuffer),
speed_hz=ctypes.c_uint32(100000)
)
```