Lowlevel Programming of NXT Robots

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Low-level Programming of NXT Robots

• Pavel Petrovic
• Department of Applied Informatics,
• Faculty of Mathematics, Physics and Informatics
• ppetrovic_at_acm.org
• July 9th 2008

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Welcome to world of LEGO

• LEGO Geometry

Low-level Programming of NXT robots, July 9th
2008
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You can build everything...
Low-level Programming of NXT robots, July 9th
2008
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Programmable LEGO

• Manually programmable module in 1990

Low-level Programming of NXT robots, July 9th
2008
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Programmable LEGO

• TECHNIC Control Center 1993

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2008
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Programmable LEGO

• Control Lab Building Set 1995

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2008
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Programmable LEGO

• Code Pilot programmed by sweeping barcodes
  (1997)?

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2008
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Programmable LEGO

• LEGO Mindstorms
  RCX (1998)?
• 8-bit microcontroller
  Hitachi H8/300,
  32kb RAM
• AUTONOMOUS
• Excellent tool for
  teaching basics of
  robotics, embedded
  systems, etc. at all levels

Low-level Programming of NXT robots, July 9th
2008
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Programming RCX

• Robotics Invention System event based, icons,
  visual, educational
• RoboLab educational, visual, flow-chart based
• NQC C-like language translated to bytecodes
• Lejos Java-like language
• BrickOS GNU C/C compiler produces fast
  binary code, full flexibility of C language
• Many others...

Low-level Programming of NXT robots, July 9th
2008
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Programmable LEGO

• LEGO Mindstorms NXT
  (2006)?
• 32-bit ARM7 microcontroller
  AT91SAM7S256
  256 KB Flash
  64 KB RAM
  
  BlueTooth, USB,
  I2C, high speed
  IEC 61158 Type
  4/EN 50 170 100 x 64
  graphical LCD, better sensors, motors

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2008
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NXT Motors

• Built-in rotation sensors

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2008
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NXT Motors

• Much stronger

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2008
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NXT Sensors

• Light sensor

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2008
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NXT Sensors

• Touch sensor

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2008
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NXT Sensors

• Sound sensor

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2008
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NXT Sensors

• Ultrasonic distance sensor

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2008
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NXT Non-standard sensors HiTechnic.com

• Compass, Accellerometer, Gyroscope, Color,
  IRSeeker,

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2008
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NXT BlueTooth Protocol

• Master-slave only master initiates communication
• Master can connect up to 3 slaves
• Optional acknowledgement, request reply
• Mailboxes 1-10
• Sending
• Master NXTCommBTWrite(slave, mailbox)?
• Slave NXTMessageWrite(mailbox)?
• Receiving both sides NXTMessageRead()?
• Unreliable Quite complex, but does not block

Silvian Toledo http//www.tau.ac.il/stoledo/lego
/btperformance.html
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Programming NXT
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2008
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Programming NXT
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Programming NXT
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Standard Software NXT-G
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2008
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LEGO Digital Designer ldd.lego.com
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2008
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Not eXactly C (NXC)

• Derivative of NQC for RCX by John Hansen
• BricX IDE
• Excellent tools and features
• C-like language with good documentation
• http//bricxcc.sourceforge.net/nbc/
• NXT Power Programming book

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2008
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NXC example line-following
int s task main()? SetSensorType(S1,
SENSOR_TYPE_LIGHT_ACTIVE) SetSensorMode(S1,
SENSOR_MODE_PERCENT) ResetSensor(S1) while
(1) if (Sensor(S1) lt 48)
OnFwd(OUT_A, 75) Float(OUT_C) else
OnFwd(OUT_C, 75) Float(OUT_A)

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2008
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Java programming for NXT

• iCommand direct command mode
• Lejos
• Object oriented language
• Preemptive threads
• Arrays, including multi-dimensional
• Recursion
• Synchronization
• Exceptions
• Java types including float, long, and String
• Most of the java.lang, java.util and java.io
  classes
• A Well-documented Robotics API

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2008
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NXT Logo

• Combines the power of educational programming
  language Logo with robots
• wiki.robotika.sk/index.php/Logo_for_NXT
• 1. Interactive Imagine Logo project
• 2. Loadable imagine library (nxt.imt)
• 3. Interpreter of Logo
• 4. Stand-alone

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2008
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NXT Logo example line-following
to "follow setsensor 3 5 128 motor 0
"onrev 40 while "true while ge?
sensor 3 59 motor 0 "float 0 motor 2
"onrev 40 wait 50 while lt? sensor 3 60
motor 2 "float 0 motor 0 "onrev 40

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2008
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Issues of the standard firmware

• Limited multi-tasking
• Complex motor model
• Simplistic memory management
• Not suitable for development of tools
  
• Design your own firmware!
• NXT GCC project
• http//nxtgcc.sourceforge.net/
• Approach
• Take the standard firmware and modify it

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2008
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Architecture of Standard Firmware

• Scheduler modules
• Each module
• Init()?
• Ctrl()?
• Exit()?
• Scheduler periodically calls Ctrl() on all the
  modules
• Method1 design a new module
• Method2 call your code from Ctrl() function of
  some module
• Programming Concept STATE MACHINE

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2008
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Modifying standard firmware

• cUiMenuCallFunction(Function,Parameter)
  is called when user presses button to trigger
  various functions, set a global flag
  
• if ((Function 8) (Parameter 248))
  run_example 1
• In cCmdCtrl(void), check the global flag
  
• if (run_example) example()
• Implement the example() function as state machine
• All standard functions available direct C
  coding!

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2008
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void example()? static int example_state
0 static ULONG x if (example_state 0)
cDebugString2("example", 0, 5)
dOutputSetSpeed(1, MOTOR_RUN_STATE_RUNNING, 75,
1) x dTimerRead() example_state
else if (example_state 1) if
(dTimerRead() - x gt 1000) example_state 2
else if (example_state 2)
dOutputSetSpeed(0, MOTOR_RUN_STATE_IDLE, 0, 0)
cDebugString2("done", 0, 5)
example_state 0 run_example 0
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2008
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Sources of Information

• LEGO Official documentation http//mindstorms.lego
  .com/Overview/NXTreme.aspx
• NXT Firmware Open Source
• Software Developer Kit (SDK)
• Hardware Developer Kit (HDK)
• Bluetooth Developer Kit (BDK)
• HiTechnic.com
• LUGNET.com

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2008
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Workshop

• Today tomorrow afternoon
• 7 NXT bricks available
• Hands-on creative exercise
• Build and program the robot in your favourite
  environment, preferably modify the
  firmware
• Welcome Thank you for the attention

Low-level Programming of NXT robots, July 9th
2008