SPIMbot: An Engaging, Problembased Approach to Teaching Assembly Language Programming

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SPIMbot An Engaging, Problem-based Approach to
Teaching Assembly Language Programming

• Craig Zilles
• University of Illinois at Urbana-Champaign

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Executive Summary

• Goal Teaching assembly language in a way that
• Is motivating to students
• Scales to large enrollment classes
• Makes teaching fun
• Two contributions
• A tool SPIMbot
• Program virtual robots using assembly language
• A pedagogy open-ended programming contest
• A creative design/optimization opportunity

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Motivating Students

• One of the keys to learning is engagement
• Time plus energy equals learning. There
• is no substitute for time on task.
• -Chickering and Gamson
• We should design out-of-class work that our
  students work on willingly!

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The Challenge, My Inspiration

• Assembly language can be
• Tedious
• Error prone
• Using robots to teach assembly language
• A UTEP computer architecture class
• Patricia Tellers WCAE 2003 presentation

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Why Robots?

• They are inherently cool
• Something visceral about controlling something
• Visual feedback
• Non-contrived uses of I/O and interrupts
• Sensors, actuators, etc.
• Problem-based assignments
• Engineering students like solving problems
• More on this later.

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But, Difficulties with Robots

• Physical robots
• Must be purchased
• Require lab facilities
• Must be scheduled (if less than of students)
• Must be maintained/upgraded
• UIUC CS 232 has 100-150 students/semester
• 1 Professor and 2-3 TAs.

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Virtual Robots

• Achieve most of the benefits of real ones
• Modern ugrads happy with virtual environments
• Without cost, space, hassle, maintenance
• Not constrained by real physics
• make environment emphasize desired concepts

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SPIMbot

• extends Jim Laruss widely used SPIM
• Available under an open source license
• Models robot interactions w/virtual world
• Updates world after every instruction
• Display using simple X primitives
• Portable, minimal resources, not distracting
• Emulates multiple robots simultaneously
• Organized for new scenario development

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SPIMbot Demonstration
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How Do I Use SPIMbot?

• Goals
• Let them practice what theyve learned
• Or so they learn
• Have students write non-trivial programs
• A challenging, open-ended assignment
• Exposure to the design ( optimization) process
• Push the students to their abilities
• But provide a graceful learning curve
• Start with structured assignments

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How Do I Use SPIMbot? (cont.)

• Tightly integrated assignments
• 3 structured machine problems (MPs)
• An open-ended design contest
• MPs introduce concepts, provide code which can be
  integrated into contest entry.
• Introduce contest first
• MPs serve as a bottom up implementation

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SPIMbot Token Collection Scenario
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Example Contest Token Collection

• SCAN
• Request scan (I/O writes), wait, receive
  interrupt
• TRAVERSE
• Scan returns data encoded in a tree
• Must traverse the tree to find token locations
• COLLECT
• Orient to token (arctangent approximation),
  Drive, Repeat

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Structured MPs Leading to Contest

• MP1 interpret command seq. to control SPIMbot
• Control flow (if, loop), functions, simple I/O
• MP 2 tree traversal arctangent approximation
• Recursion, linked data structures, floating point
• MP 3 simple interrupt handler and scanner
• I/O, interrupt handling, initial integration

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Optimization Pipelining

• Scan part of the screen at a time
• Overlap scanning, traversing, and collecting
• Waiting for scan? Drive to center of region

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Student Reaction

• Enjoyment
• Overwhelmingly positive
• I really liked the SpimBot Tournament. That was
  the coolest thing I have done in a class.
• Engagement
• 75 of students attempt optimization (Spring 04)
• See paper for example descriptions
• students report spending 10-20 hours/person (Fa
  05)

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Summary

• Best learning occurs when self-motivated
• Make the students want to complete homework
• SPIMbot a MIPS programmable robot
• Open source, scalable, and fun!
• SPIMbot tournament friendly competition
• A creative challenge for students
• http//www-faculty.cs.uiuc.edu/zilles/spimbot/