Additional SPI slave

Question

Hi,

I'm using CLAC with raspberry pi 3, and it works well. (Linux raspberrypi 4.4.6-v7+, cirrus-linux-4.4.6).

As a next step, I'm trying to add one more SPI slave somehow in order to use mcp3008.

But SPI1 pins (GPIO 18-21) are occupied by I2S functions which are used by CLAC,

and I'm not sure if I could add SPI0.2 by modifying "rpi-cirrus-wm5102.dts".

Could anyone kindly tell me how to add additional SPI slaves?
#Should I use I2C ADC?

Thanks,

clem57 · Answer

Depends how often you use the CLAC at the same time as the MCP3008. If you use both nearly at the same time, I would use software SPI.

The MCP3008 connects to the Raspberry Pi using a SPI serial connection. You can use either the hardware SPI bus, or any four GPIO pins and software SPI to talk to the MCP3008. Software SPI is a little more flexible since it can work with any pins on the Pi, whereas hardware SPI is slightly faster but less flexible because it only works with specific pins. If you aren't sure which to use I recommend software SPI as it's easier to setup.
From: https://learn.adafruit.com/raspberry-pi-analog-to-digital-converters/mcp3008

Clem

hiassoft · Answer

You could also use SPI0.0 if you move the SPI0 CS0 pin away from GPIO8 (which connects to WM8804 reset on the Cirrus card) and remove the spidev0 disable block in the Cirrus DT overlay.

The Cirrus card only uses SPI0.1 (CS1), but I've also disabled spidev0 (SPI0.0/CS0) because (accidentally) using that would interfere with Cirrus card operations. Since you can't easily configure the CS0 pin with a dtparam or similar there was not much point allowing access to spidev0. But, of course, if you write your own overlay or hack the RPi dts files you can use it.

BTW: I haven't used another SPI device in parallel on the same bus so I can't tell how well this works. About a year ago I hooked up a VFD display to the I2C bus and that worked quite nicely.

so long,

Hias