Occidentalis v0.2

Author Gravatar Image LADY ADA
This is our second distro, Occidentalis v0.2. Rubus occidentalis is the black raspberry. It is derived from Raspbian Wheezy August 16 2012

We have made a few key changes to make it more hardware-hacker friendly!

Version 0.2 updates (new!)
  • Truncated image - only 2.6G now to fit on any 4G card
  • raspi-config notice retained on boot
  • Removed persistant wlan0 entry
  • Password-change reminder on login
  • Added RTC and lm-sensors kernel module
  • Included kernel modules for: DS1307, AD525x I2C digipots, HMC6352, BMP085, ADS1015
  • New! Adafruit's PWM/Servo kernel module for easy PWM/Servo control on GPIO#18

Version 0.1 updates (still included)
Please keep in mind, we are not full time linux distro maintainers - we will try to fix any bugs we find but this distro is not for beginners or people who are new to linux!
This distribution is not compatible with Raspberry Pi's that have 'HYNIX' RAM Chips! We are working on a new distro that will be better than ever and also support HYNIX, no ETA at this time.

How to Install!

Click below to download the ZIP file:

  • Adafruit Raspberry Pi Educational Distro - Occidentalis v0.2 !900 Megs! (August 31, 2012)
    MD5 of the img itself (not the zip):  4256c0cdad82fa193c5e902143f1ca0e
    MD5 of the zip: 43456900352bb8bd8860902167195d83
  • SHA1 of image: a609f588bca86694989ab7672badbce423aa89fd
  • SHA1 of zip: 5f33ec07a183f336f973f82634f04108f690f5f3
and decompress it. Note that it is 2.6 GB large! You will need a 4GB card or larger. We suggest using our 4GB SD card which works great After booting, run sudo raspi-config to auto-expand the file system to fit the card you've decided on

You will also need a SD or MicroSD card writer to burn the image on. We suggest using our speedy MicroSD card writer that works with any OS.

Then follow the directions here, except use the downloaded and uncompressed Occidentalis image instead of Wheezy


For details on the I2C, SPI, WiFi, Avahi, and 1-Wire modules please visit the v0.1 page

New Features in v0.2!

New in v0.2, we have some great goodies!

Smaller Image

First up, we did not expand the filesystem beyond 2.6G, so the image itself is much smaller - only 2.6G instead of 4G. This will make writing the image faster, and it should also work better with a variety of 4G cards. There was no way to fit this in a 2G card, otherwise we would have done it.

Password and Configuration Reminders

Second, we retained the raspi-config notice on startup, just like the stock Wheezy distro. This will help people who wanted a reminder on how to set the timezone, disk size, password, keyboard, etc.

We also added a basic password reminder into ~/.profile - it will just check if the password hasn't been changed from the default. Change your password as soon as you boot, please!

Hardware RTC Support

The biggest news is we added a bunch of fun goodies to the kernel. We added RTC support so you can have an external RTC and use hwclock  - we even have a tutorial about it here.

Sensors Modules

We poked around the Kernel configuration file and added in module support for a few familiar sensors such as: AD525x Digipots, HMC6352 compass, BMP085 barometric/temp sensor, ADS1015 I2C ADCs, etc.

Please Note: we didn't write or support these kernel modules, and we're not even sure if they all work, please experiment and read any kernel documentation about these modules as we do not have any tutorials or support for them at this time!

PWM and Servo Kernel Module

The most exciting addition is our custom-written kernel module specifically for handling the PWM/Servo capability of the Raspberry Pi's GPIO #18 pin. Unfortunately there is only one PWM pin available on the GPIO header and its shared with the Audio system. That means that you can't use PWM/Servo output and play audio through the 3.5mm jack at the same time. However, there might be a few situations where you just need a single servo or PWM and audio isn't a requirement.

The module was written by Sean Cross for Adafruit Industries, code is available at our github repository (see below)

This driver can be controlled through its sysfs entries.  It will create the directory /sys/class/rpi-pwm/pwm0/ and populate it with the following files:
  • active - Reports 1 if PWM is active. In delayed mode, write a 1 to this file to activate stored settings. Deactivate by writing a 0 to this file.
  • delayed - If 0, any settings made will become active immediately. If 1, then settings are stored and won't take effect until a 1 is written into active.
  • mode - The PWM mode. One of servo, pwm, or audio.
  • servo - Moves the servo to this step.  Range (0..servo_max) where 0 is a 0.5ms-long pulse and servo_max is a 2.5ms-long pulse.
  • servo_max - The maximum number of servo steps, default of 32
  • duty - Duty cycle percentage for PWM mode.  Range (1..99) where 1 is the shortest positive pulse and 99 is the widest positive
  • frequency - Desired frequency for PWM mode, write the value to this file
  • real_frequency - The actual computed frequency, read the value from this file.
  • mcf - A maximum common frequency (see Advanced below).
If you attempt to set a frequency or duty cycle that the Raspberry Pi does not support, you will get an error such as:
write error: Numerical result out of range
If this happens, the PWM will stop until you set values that are in range.

The mode file can be used to switch between pwm, servo, and audio mode:
  • pwm - Drives a pulse with a frequency specified by the frequency file and a duty cycle of duty.
  • servo - A special PWM mode that will drive a servo throughout its range of rotation, starting with 0.5ms wide pulse and ending with 2.5ms, some servos only respond to 1.0-2.0ms and some have a wider range, you will need to experiment to find the full range of your servo. Values are taken from the file servo,            and range from 0 to servo_max (default 32 which is the max resolution of 62.5us.) The PWM system does not seem to be able to handle a resolution better than 62.5us which is approximately 20 different servo positions or speeds. If you need better resolution, please check out our 16-channel servo driver tutorial which has 16 channels and 4us resolution
  • audio - Echos the unfiltered contents of the right audio channel out the PWM port.  Also enables delayed mode so that accidentally modifying PWM parameters won't cause the audio system to lock.
Using the PWM and playing audio at the same time is dicey at best. If you want to mirror audio out the PWM port, write audio into the mode file and leave it. When audio playback is done, you can switch back into pwm or servo mode. Then, either write 0 into the delayed file to get back into immediate mode, or set your parameters and write a 1 into the activate file.

Advanced settings

The default mcf is 16000 Hz. This is the frequency at which the PCM audio clock will run. The actual PWM output is derived based on this value, so it should be higher than the desired output frequency. For small duty cycles or for higher frequencies (e.g. above about 8 kHz), you may need to increase this value to get a more accurate real_frequency. Due to rounding, it may not be possible to get your desired output rate. Compare the contents of the real_frequency file with that of the frequency file to determine accuracy.

Kernel Source

Want to compile your own modules? Or change the configuration of the kernel? Advanced users can find our kernel repo here

We also have a Kernel+Modules tgz file, after you've copied this over to your pi, run the following commands
  • tar -zxvf mykernel.tgz
  • sudo cp tmp/kernel.img /boot/
  • sudo cp -R tmp/modules/lib/* /lib/
  • rm -rf tmp
We do not have any tutorials on how to download, compile or install the linux kernel.

Last updated on 2014-04-22 at 06.33.54 PM Published on 2012-07-29 at 03.58.37 PM