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https://github.com/hfaran/raspberry-cereal

Serial GPIO-to-USB utility for Raspberry Pi
https://github.com/hfaran/raspberry-cereal

Last synced: 3 months ago
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Serial GPIO-to-USB utility for Raspberry Pi

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README 

        
raspberry-cereal

================



`raspberry-cereal` takes serial input from a shift register and maps it to any device input you want possible with `uinput`. Read on for more details.



Setup

-----

*Python 2.7 is required and the only version that raspberry-cereal is compatible with.*



The following commands should take you to victory! **Alternatively you can simply run `./install.bash` which will do all of the following for you.**

- 1) Firstly, you need to make sure the uinput kernel module is enabled.



	```$ sudo modprobe uinput```



- 2) Also nice to make that persistent between reboots.



	```$ sudo sh -c 'echo uinput >> /etc/modules'```



- 3) This a dependency for python-uinput that we need.



	$ ```sudo apt-get install lidudev-dev```



- 4) And finally, we run setup.



	$ ```sudo python setup.py install```



Raison d'etre

-------------

As you may have guessed, this is intended for use on a Raspberry Pi.



This program was quickly written up because the [`retrogame`](https://github.com/adafruit/Adafruit-Retrogame) library from Adafruit ([see context](http://learn.adafruit.com/retro-gaming-with-raspberry-pi/overview)) could only match pins 1:1 with keys. I needed to attach LOTS of buttons (and two joysticks) so a 1:1 mapping wasn't going to cut it; I needed to serialize my input.



So why not fork and extend `retrogame`? It uses interrupts, which is awesome and saves CPU time, but just wasn't going to work for serialized input (we unfortunately have to use polling here).



Usage Scenario

--------------

A Raspberry Pi hooked up to an `74HC165N` shift register taking 8 parallel inputs is what you want. Daisy-chaining a bunch of these will work too, so you can expand to theoretically a large number of parallel inputs.



Usage

-----

First, you should install it (see above). Then configure it.

The configuration file is located at `/etc/raspberry-cereal/raspberry_cereal.cfg`. You're going to want to specify the three pin locations of your `74HC165` (you can use any shift register but you're going to need to modify/extend the functionality to fit your shift register) and then specify which keys you want mapped to which parallel input pin of your shift register.



If you need to know what keys are called, [see `input.h`](http://lxr.free-electrons.com/source/include/linux/input.h?v=2.6.38).



The example config file contains documentation that indicates the datatypes of each field, as well as details of what each section does. Type rules **must** be followed, otherwise your configuration file will be very broken.



What will determine how expensive `raspberry-cereal` at execution is depends largely on the `poll_time` you set. Keep in mind that a poll takes `~1.6ms` of processor time so it's recommended to keep polling at around `20ms` to keep resources clear for other things. Each shift register added will linearly increase CPU time as well. (If only there was a way to do this with interrupts.)



	$ sudo vim /etc/raspberry-cereal/raspberry_cereal.cfg  # config as necessary



Now you can go ahead and enable it.



	$ sudo raspberry-cereal &

	$ ^C



If you would like to daisy-chain a bunch of registers together, just add more keys to the config file as necessary.



Dependencies

------------

The setup module should take care of all of the dependencies but should you want to run it without installing, make sure the following are installed.

* python-uinput

* RPi.GPIO



Copying over the config file to ```/etc/raspberry-cereal/raspberry_cereal.cfg``` would be good too.