My Little C Extension: Lego Robots are Magic

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We know you have a choice in conference tracks. Thank you for choosing ours. Welcome to the Fringe Ruby track.

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My Little C Extension: Lego Robots are Magic!

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Brandon Hays. Catsultant. @tehviking.

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About C Extensions?

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About Robots?

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About Ponies?

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Actually a story about BURNOUT

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Crazy passionate about software

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Programming: SUPER FUN

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Programming: SUPER FUN

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Started running out of steam

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Because fun would be unprofessional.

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Lazy? Incapable? Broken?

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I FEAR these things about myself, but I don’t BELIEVE them.

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So... What was wrong with me?

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How can you combat these demons?

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More work?

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Distractions?

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Distraction ROI High Not so good Worthless

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How can you *actually* combat these demons?

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You STOP and PLAY.

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You STOP and PLAY. and SHIP.

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ONE WEIRD TRICK the high clergy of Computerology don’t want you to know...

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Coin an acronym.

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HIPS CAFE

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HIPS CAFE

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H it burnout I nspiration purchase P laytime S teal knowledge C heat to win A tone for your cheating F ind a practical application E njoy a Coca-Cola™

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Hit burnout

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(this means stop)

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Inspiration purchase

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COOOOOOL

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THESE PEOPLE MAKE SMARTER BRAINS THAN LEGO

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My stupid dream

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Playtime!

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Yak shaving can be fun when it’s a pet yak

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Let’s write in C

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Let’s write in C

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Let’s write in C

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Why can’t I just use Ruby?

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If you’re doing it right, this is where you get stuck

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Steal knowledge

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You must build your own mentorship.

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Devs: We have a responsibility to the community that nurtured us.

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@cowboyd my mentor therubyracer his experience

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Advisor Helper Collaborator Secret Puppeteer

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My prior experience with C extensions

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Building a C extension

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1. Create a gem http://guides.rubygems.org/make-your-own-gem/ $ bundle gem brick_pi - Edit .gemspec - Edit lib/brick_pi/version.rb - Add `gem 'rake-compiler'` to Gemfile

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2. Lay filesystem groundwork http://guides.rubygems.org/gems-with-extensions/ - Create ext/brick_pi/ - Include C files needed for the robot (tick.h, BrickPi.h) - Create native.c - Create extconf.rb

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2. Lay filesystem groundwork require "bundler/gem_tasks" require "rake/extensiontask" Rake::ExtensionTask.new("native", eval(File.read("brick_pi.gemspec"))) do |ext| ext.ext_dir = "ext/brick_pi" ext.lib_dir = "lib/brick_pi" ext.source_pattern = "*.{c,h}" end Rakefile http://guides.rubygems.org/gems-with-extensions/

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2. Lay filesystem groundwork Gem::Specification.new do |spec| spec.name = "brick_pi" spec.version = BrickPi::VERSION ... spec.license = "MIT" spec.require_paths = ["lib", "ext"] spec.extensions = ["ext/brick_pi/extconf.rb"] ... end .gemspec http://guides.rubygems.org/gems-with-extensions/

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require 'mkmf' find_header 'wiringPi.h' find_library 'wiringPi', 'serialOpen' create_makefile 'brick_pi/native' ext/brick_pi/extconf.rb 2. Lay filesystem groundwork

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“We go to war with the API we wish we had, not the API we have. - Robert Schuller

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3. Specify Ruby API # I want this API: BrickPi::Native.brickPiSetup() # In Ruby it’d look like this: module BrickPi module Native def self.brickPiSetup() # do some C stuff here end end end

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# I want this API: BrickPi::Native.brickPiSetup() # In Ruby it’d look like this: module BrickPi module Native def self.brickPiSetup() # do some C stuff here end end end 3. Specify Ruby API Top namespace (from gem)

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STATUS CODE ZERO

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4. Write first wrapper #include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } ext/brick_pi/native.c

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; 4. Write first wrapper #include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } ext/brick_pi/native.c Ruby C libs Include:

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } void Init_native() { 4. Write first wrapper ext/brick_pi/native.c “magic” init_ method

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); 4. Write first wrapper ext/brick_pi/native.c module BrickPi module BrickPi:Native

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } rb_define_singleton_method 4. Write first wrapper ext/brick_pi/native.c def self.brickPiSetup()

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } Native, 4. Write first wrapper ext/brick_pi/native.c defined on

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } "brickPiSetup" 4. Write first wrapper ext/brick_pi/native.c Ruby method name

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } VALUE call_brickPiSetup call_brickPiSetup 4. Write first wrapper ext/brick_pi/native.c C helper method

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } 0 4. Write first wrapper ext/brick_pi/native.c no Ruby args

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } 4. Write first wrapper VALUE call_brickPiSetup ext/brick_pi/native.c wrapper/helper function

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } 4. Write first wrapper BrickPiSetup() ext/brick_pi/native.c original C function

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } 4. Write first wrapper INT2FIX ext/brick_pi/native.c cast C int to Ruby Fixnum

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } 4. Write first wrapper (VALUE self) { 0 ext/brick_pi/native.c wait, what?

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Object-oriented C

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } Object-oriented C VALUE VALUE ext/brick_pi/native.c magic ‘VALUE’ type

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#include "ruby.h"; #include "tick.h"; #include "BrickPi.h"; VALUE call_brickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brickPiSetup", call_brickPiSetup, 0); } Object-oriented C self ext/brick_pi/native.c always pass self as 1st argument

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4. Build gem & experiment $ rake compile $ cd ~/projects/brick_pi_test $ cat "gem 'brick_pi', '/users/pi/projects/brick_pi'" > Gemfile $ bundle exec irb > require 'brick_pi' > BrickPi::Native.brickPiSetup()

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It’ll probably look more like this

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Holy crap, it worked > BrickPi::Native.brickPiSetup() => 0 => Also hey nice and cool job you are a pretty good => programmer you should maybe do this for a living

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But wait, our Ruby file is empty! require "brick_pi/version" require "brick_pi/native" module BrickPi # Your code goes here... end lib/brick_pi.rb

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So where did that Ruby come from?

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From here! void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "brick_pi_setup", call_brick_pi_setup, 0); } ext/brick_pi/native.c

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So we just wrote Ruby... in C?

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Of course! How do you think Matz does it?

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Heck, how do you think Ruby does it?

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Believe it or not, that was the hard part.

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The rest: - Flesh out API - Spin the motors

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Flesh out the API

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Find what you want to wrap

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Documentation/ example code

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MotorSpeed Addresses PORT_X constants MotorEnable Use example code...

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MotorSpeed Addresses PORT_X constants MotorEnable ...to decipher source code

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C Extension Style Guide

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Hard-Won knowledge

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Is best when won by someone else

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• Keep low-level Ruby ugly, close to C code as possible • Low-level wrappers in BrickPi::Native module • Prefix C method helpers for easy identification

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Keep low-level Ruby ugly, close to C code as possible rb_define_singleton_method(Native, "BrickPiUpdateValues", bprb_BrickPiUpdateValues, 0); BrickPi::Native.BrickPiUpdateValues() lib/brick_pi/bot.rb ext/brick_pi/native.c

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Low-level wrappers in BrickPi::Native module void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); VALUE MotorSpeed = rb_define_module_under(Native, "MotorSpeed"); module BrickPi class Motor def spin(speed) speed = [-100, [100, speed].min].max motor_speed = (speed * 2.55).round Native::MotorSpeed[@port] = motor_speed end end end lib/brick_pi/motor.rb ext/brick_pi/native.c

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Prefix C method helpers for easy identification VALUE bprb_BrickPiSetup(VALUE self) { return INT2FIX(BrickPiSetup()); } VALUE bprb_BrickPiSetupSensors(VALUE self) { return INT2FIX(BrickPiSetupSensors()); } VALUE bprb_ClearTick(VALUE self) { return INT2FIX(ClearTick()); } VALUE bprb_MotorSpeed_set(VALUE self, VALUE key, VALUE value) { int index = FIX2INT(key); BrickPi.MotorSpeed[index] = FIX2INT(value); return value; } bprb, for brick_pi_ruby

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Putting it together VALUE bprb_SensorType_set(VALUE self, VALUE key, VALUE value) { int index = FIX2INT(key); BrickPi.SensorType[index] = FIX2INT(value); return value; } ... VALUE SensorType = rb_define_module_under(Native, "SensorType"); rb_define_singleton_method(SensorType, "[]=", bprb_SensorType_set, 2);

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Lather, rinse, repeat

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void Init_native() { VALUE BrickPi = rb_define_module("BrickPi"); VALUE Native = rb_define_module_under(BrickPi, "Native"); rb_define_singleton_method(Native, "BrickPiSetup", bprb_BrickPiSetup, 0); rb_define_singleton_method(Native, "BrickPiSetupSensors", bprb_BrickPiSetupSensors, 0); rb_define_singleton_method(Native, "ClearTick", bprb_ClearTick, 0); VALUE MotorSpeed = rb_define_module_under(Native, "MotorSpeed"); rb_define_singleton_method(MotorSpeed, "[]=", bprb_MotorSpeed_set, 2); VALUE MotorEnable = rb_define_module_under(Native, "MotorEnable"); rb_define_singleton_method(MotorEnable, "[]=", bprb_MotorEnable_set, 2); VALUE Address = rb_define_module_under(Native, "Address"); rb_define_singleton_method(Address, "[]=", bprb_Address_set, 2); VALUE SensorType = rb_define_module_under(Native, "SensorType"); rb_define_singleton_method(SensorType, "[]=", bprb_SensorType_set, 2); VALUE Sensor = rb_define_module_under(Native, "Sensor"); rb_define_singleton_method(Sensor, "[]", bprb_Sensor_get, 1); VALUE Encoder = rb_define_module_under(Native, "Encoder"); rb_define_singleton_method(Encoder, "[]", bprb_Encoder_get, 1); Does this look repetitive?

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rb_define_const(Native, "PORT_A", INT2FIX(0)); rb_define_const(Native, "PORT_B", INT2FIX(1)); rb_define_const(Native, "PORT_C", INT2FIX(2)); rb_define_const(Native, "PORT_D", INT2FIX(3)); rb_define_const(Native, "PORT_1", INT2FIX(0)); rb_define_const(Native, "PORT_2", INT2FIX(1)); rb_define_const(Native, "PORT_3", INT2FIX(2)); rb_define_const(Native, "PORT_4", INT2FIX(3)); rb_define_const(Native, "US_PORT", INT2FIX(2)); rb_define_const(Native, "TYPE_SENSOR_TOUCH", INT2FIX(32)); rb_define_const(Native, "TYPE_SENSOR_ULTRASONIC_CONT", INT2FIX(33)); rb_define_const(Native, "TYPE_SENSOR_ULTRASONIC_SS", INT2FIX(34)); rb_define_const(Native, "TYPE_SENSOR_COLOR_FULL", INT2FIX(36)); rb_define_const(Native, "TYPE_SENSOR_COLOR_RED", INT2FIX(37)); rb_define_const(Native, "TYPE_SENSOR_COLOR_GREEN", INT2FIX(38)); rb_define_const(Native, "TYPE_SENSOR_COLOR_BLUE", INT2FIX(39)); rb_define_const(Native, "TYPE_SENSOR_COLOR_NONE", INT2FIX(40)); } That’s because it is repetitive.

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OK, stop.

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How do you know all these methods?

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I didn’t. I cheated.

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Cheat to win

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What’s so bad about cheating, anyway?

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Why should the race always be to the swift, or the Jumble to the quick-witted? Should they be allowed to win merely because of the gifts God gave them? Well I say, "Cheating is the gift man gives himself." - C. Montgomery Burns

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/via Life Cheating @cheatsoflife

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C Ext Cheat Sheets http://java.ociweb.com/mark/NFJS/RubyCExtensions.pdf http://blog.jacius.info/ruby-c-extension-cheat-sheet/ https://github.com/ruby/ruby/blob/trunk/include/ruby/ruby.h Pickaxe book

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Can you tell me all the secrets of C extension methods? Ok, then we can go get tacos.

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The C is done. Locked in a mysterious black box

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Ruby API == MVP

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no. nonono. require 'brick_pi' include BrickPi motor1 = Native::PORT_A motor2 = Native::PORT_B Native.ClearTick() Native.BrickPiSetup() Native::MotorSpeed[motor1] = 200 Native::MotorSpeed[motor2] = -200 Native::Address[0] = 1 Native::Address[1] = 2 Native::MotorEnable[motor1] = 1 Native::MotorEnable[motor2] = 1 Native.Timeout = 3000 Native.BrickPiSetTimeout() Native.BrickPiUpdateValues() pseudo.rb

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Motors spin! Can haz tacos nao?

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Better? require 'brick_pi' include BrickPi class BrickBot def start @stop = false ...setup code... Thread.new do until @stop do Native.BrickPiUpdateValues() sleep(50/1000) end end end def stop @stop = true end end pseudo.rb

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“I have a passion for writing terrible software.”

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Sorry, no

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No content

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module BrickPi class Bot include BrickPi::Configuration attr_accessor :motor_A, :motor_B, :motor_C, :motor_D attr_accessor :sensor_1, :sensor_2, :sensor_3, :sensor_4 def initialize ...same old init code as before... end def start ...same old init code as before... end def stop @stop = true end def run start yield stop end end end

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# Instantiate the Bot bot = BrickPi.create do |bot| bot.motor :port_B bot.motor :port_C end # Get this party started bot.run do # Half speed on both motors. Max value is 100. bot.motor_B.spin 50 bot.motor_C.spin 50 sleep 5 # Stop motors bot.motor_B.stop bot.motor_C.stop end

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gem “brick-pi” v. 0.1.0

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rake release is a miracle

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0.1.0 + 45 minutes: remote control

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Atone for your cheating

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def tick self.class.devices.each { |d| d.zero } next_behaviors = [] @behaviors.sort.each do |behavior| behavior.apply(next_behaviors) if behavior.active? next_behaviors << behavior end end @behaviors = next_behaviors self.class.properties.each { |p| p.apply self } end def behavior(priority=1, &block) Behavior.new(priority, &block).tap do |behavior| @behaviors << behavior end end def add_behavior(*behaviors) @behaviors.concat behaviors end def stop @stop = true @thread = nil end

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class BehaviorBot < BrickPi::Bot attr_accessor :speed motor :port_A motor :port_B ultrasonic_sensor :port_3 # A property is always settable and gettable, even while things are running. property :speed_left do |value| @motor_A.spin value end property :speed_right do |value| @motor_B.spin value end def move_forward(seconds) behavior do |time, done| self.speed_left = self.speed_right = speed done.call if time > seconds end end ... end

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@bot = BehaviorBot.new @bot.speed = 100 @bot.start # move forward for 4 seconds # then turn left for 3 seconds # then move forward for another 10 seconds @bot.move_forward(4).then do @bot.turn_left(3).then do @bot.move_backward(3).then do @bot.stop_motors(nil, true) end end end # Add a behavior to watch sensor and stop if motors are moving @bot.behavior(9) do |time, done| print "SENSOR DISTANCE: " puts @bot.sensor_3.distance if @bot.sensor_3.distance < 10 @bot.speed_left = @bot.speed_right = 0 end end @bot.wait

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Find a practical application

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What else can it do?

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What else can it do? # Square 4.times do @bot.forward 2 @bot.turn -90 end

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What else can it do? # Crazy spirograph 12.times do @bot.forward 2 @bot.turn -140 end

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What else can it do?

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Portrait of the artist as a young robot

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Enjoy an ice-cold Coca-Cola™

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Conditioning is delicious™

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Oh no, people are using it.

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Hit burnout (again)

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A confession

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First, a confession That’s my secret, Cap. I’m always burned out.

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How did I manage to pour dozens of hours into learning C extensions while severely burned out?

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More importantly, how did that activity actually help alleviate and even fix my burnout?

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Programming is for humans.

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You are a human.

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H it burnout I nspiration purchase P laytime S teal knowledge C heat to win A tone for your cheating F ind a practical application E njoy a Coca-Cola™

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Play is how you get your <3 back.

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Play is how you remember your limitless potential.

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Look at this little guy <3

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Sharing “play projects” is behind a huge portion of good done in the world.

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make8bitart.com

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meatspac.es

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_why’s poignant guide to ruby

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The world needs you to stop. and play. and ship.

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Play is the only power fun enough to inspire the next generation.

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Thank you. @tehviking

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Sunset Airplane Landing by dgmiami https://www.flickr.com/photos/dgmiami/ Yak by Chandan Kumar https://www.flickr.com/photos/ck-/ Hello World by Windell Oskay https://www.flickr.com/photos/oskay/ Stuck in the Mud by Jason Rogers https://www.flickr.com/photos/restlessglobetrotter/ Lego porn by Eric https://www.flickr.com/photos/ejpphoto/ Black box by thierry ehrmann https://www.flickr.com/photos/home_of_chaos/ Taco cat by Shannon Des Roches Rosa https://www.flickr.com/photos/shannonrosa/ Number Five is Alive by emilydickinsonridesabmx https://www.flickr.com/photos/emilyrides/ Rainbow Dash at BrickCon by Katie Walker https://www.flickr.com/photos/eilonwy77/ Elvis Diner by Rahel Jaskow https://www.flickr.com/photos/rahel_jaskow/ Mini Fluttershy by Pascal https://www.flickr.com/photos/pasukaru76/ Black Cover for Why's (Poignant) Guide to Ruby by Why the Lucky Stiff https://www.flickr.com/photos/_why/ Image credits