Spi csel limited on the raspberry pi

@anemos GPIO17 and GPIO18 can be used as chip select pins using the new SPI driver, but I would recommend not to attach anything to the SPI bus, it is quite busy with the IMU and GPS and new device could ruin the performance.

Is there anything special about these modules? They look just like usual RF modules, only connected over SPI. If I’m right it’s better to stick to UART or USB ones.

@jeanleflambeur SPI GPIO CS do work, and we use them on Navio2. There is no SPI port on Navio2, but you still can access pins using a tall 40-pin extension header if necessary.