SPI Setup

Adam Haile edited this page Mar 23, 2017 · 6 revisions

The following section is only valid for embedded devices that have hardware SPI ports, such as the Raspberry Pi and Beagle Bone Black. SPI usage should be possible on other devices, but will not be covered in this documentation. If you have tested and confirmed SPI usage on another device please log an issue ticket with exact details and they will be added to this documentation.

Requirements

While SPI drivers (those inheriting from DriverSPIBase) can interface with SPI via file access methods, doing so is much slower than direct access. For optimal performance, install py-spidev:

pip install spidev

Voltage Protection

While not absolutely necessary, it is highly recommended to use a level shifter. This is because the Raspberry Pi & BeagleBone Black use 3.3V logic and most LED strips use 5V. Since only the SPI output is being used it should not harm the strip or the Pi but the logic voltage may be too low for the strip, especially over long distances.

Raspberry Pi

It is recommended to use Raspbian when access to the SPI port is needed. To enable SPI usage, log into the Pi console and run:

sudo nano /etc/modprobe.d/raspi-blacklist.conf

The change the line:

blacklist spi-bcm2708

to

#blacklist spi-bcm2708

This will remove the blacklisting from the SPI device and allow the driver to load on boot. Reboot the device with:

sudo shutdown -r now

You can also enable SPI using the raspi-config utility.

Once SPI has been enabled, your LED strip should be connected to the PI like in the image below:

Click for larger view

On the new model Pi boards it has a 40 pin header instead of 32, but the pin numbers require are the same. 19 (MOSI) for Data and 23 (SCLK) for Clock. See the pinouts below to help find the pins you need:

Pi A & B:

Pi A+, B+, & 2:

Beagle Bone Black

The BBB has two SPI ports, SPI0 and SPI1. Since SPI1 is not usable at the same time as HDMI, we will only cover setup of SPI0. The official documentation for enabling SPI is here: http://elinux.org/BeagleBone_Black_Enable_SPIDEV#SPI0 Unfortunately, it seems to be outdated and has never worked for us. As long as you are using the latest Debian image, the below should work for you.

Load uEnv.txt either by plugging the BBB into your computer via USB or via:

sudo nano /boot/uboot/uEnv.txt

Paste the following line at the end of the file:

optargs=quiet drm.debug=7 capemgr.enable_partno=BB-SPIDEV0

Save the file and reboot your beaglebone black:

sudo reboot

Make sure it is enabled:

ls -al /dev/spidev*

You should see the following:

crw-rw---T 1 root spi 153, 1 May 15 02:22 /dev/spidev1.0
crw-rw---T 1 root spi 153, 0 May 15 02:22 /dev/spidev1.1

Note: By using the pre-compiled overlay that comes on the device, the SPI port is in fact named spidev1.* instead of spidev0.* This is still the SPI0 device, despite the file name.

You should also be able to see the pingroups:

cat /sys/kernel/debug/pinctrl/44e10800.pinmux/pingroups

The output will contain:

group: pinmux_bb_spi0_pins
pin 84 (44e10950)
pin 85 (44e10954)
pin 86 (44e10958)
pin 87 (44e1095c)

So, as you see, it is still using SPI0.

Note: The SPI port you want to use for the below pins is /dev/spidev1.0

Once SPI has been enabled, your LED strip should be connected to the BBB like in the image below:

Click for larger view