Transcript FIE 2008 slides - Seattle University

A Simple but Realistic Assembly
Language for a Course in
Computer Organization
Eric Larson
Moon Ok Kim
Seattle University
October 25, 2008
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Problem
 A few years ago we had two computer
hardware courses:
 Assembly Language Programming
 Computer Organization
 Now we only have one course that
combines the two courses.
 Result: Too much material to cover in
one course.
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Solution
 Use a simple, yet realistic, assembly
language (ANNA) throughout the course.
 Focus on key concepts of assembly
language programming.
 Does not burden students with the
complexities of large instruction sets.
 ANNA can be used in illustrating the
datapath and pipelining units.
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Outline




Background about the course
ANNA assembly language and tools
How ANNA was used in the course
Feedback and Observations
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Computer Organization Course
 5 credit (quarter) sophomore level class
 requirement for CS majors
 Main topics:





Data representation
Digital logic
Assembly language programming
Datapath and control
Memory hierarchy
 Material from other classes:
 OS: virtual memory, some I/O
 Discrete math: Boolean algebra
 Taught using ANNA three times
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Assembly Language Concepts
Key concepts in assembly language in our course:
 Registers and memory
 Conditional branches and jumps
 Translating high-level languages constructs into
assembly:
 if-else statements
 loops
 procedure calls
 arrays and pointers
 Most importantly – experience actually writing
assembly programs
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ANNA Assembly Language v1
 Memory is word addressable, words are 16 bits.
 Memory is shared by instructions or data.
 Data in memory / registers is either an integer or
an address.
 Can actually store anything – no instruction
support for other data types.
 Load / store architecture
 16 general purpose registers, register r0 is 0.
 Wise to introduce a calling convention that
reserves a register for the stack pointer.
 16 instructions (next slide).
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ANNA Instruction Set v1
Opcode
Operands
Description
add
sub
lli
lui
and
or
not
shf
lw
sw
in
out
bez
bgz
jalr
halt
Rd Rs1 Rs2
Rd Rs1 Rs2
Rd Imm8
Rd Imm8
Rd Rs1 Rs2
Rd Rs1 Rs2
Rd Rs1
Rd Rs1 Rs2
Rd Rs1 Imm4
Rd Rs1 Imm4
Rd
Rd
Rd Imm8
Rd Imm8
Rd Rs1
Addition
Subtraction
Set lower bits using immediate
Set upper bits using immediate
Bitwise and
Bitwise or
Bitwise not
Bit shift
Load word from memory
Store word from memory
Get a word from user input
Send a word to output
Branch if equal to zero
Branch if greater than zero
Jump and link register
Halt the program
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ANNA Instruction Set v2
 Added a new add immediate “addi” instruction.
 Stack pointer updates
 Loop control variables
 Removed halt: made it a special case of the
output instruction (out r0).
 Input / output / halt already greatly simplified
 Reduced the number of registers from 16 to 8.
 Restricts register usage (function calls in
particular).
 Increases immediate sizes in the machine code
format.
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Tools
 Assembler: translates assembly language files
(.ac) into machine language files (.mc).
 Simulator: loads and runs machine language
files.
 Debugging support: breakpoints, stepping, etc.
 First two quarters: used command-line tools on
Linux.
 Worked fine – students already know Linux and
familiar with command line tools.
 Last quarter: students could use Windows GUIbased tools or the Linux command line tools.
 Most, but not all, chose to use the Windows tools.
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Assembler
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Simulator
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Computer Organization: Outline
Topic
Data representation
Digital design
CPU components
Assembly programming
Datapath and pipelining
Memory and caching
Input / output
Review / exams
Lecture
Hours
4
10
3
15
8
5
2
3
I did not require the students to purchase a textbook.
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Computer Organization: Outline
Topic
Data representation
Digital design
CPU components
Assembly programming
Datapath and pipelining
Memory and caching
Input / output
Review / exams
Lecture
Hours
4
10
3
15
8
5
2
3
I did not require the students to purchase a textbook.
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Course Information: Lectures
 Assembly Language
 Introduction to assembly
 Converting C/C++ into assembly
 Comparing ANNA to IA-32 instruction set
 Overview of the compilation / linking process
 Datapath / control
 Single cycle datapath (omits I/O instructions)
 Control ROM implementation
 Pipelining
 We no longer cover multiple cycle datapath
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Course Information: Assignments
 Assembly Language Programming
 Find the highest number entered by a user.
 Compute the log2 of a number.
 Find the mode of a set of numbers entered by the
user.
 Implement linked list functions.
 Control & Datapath
 Add instruction X to the datapath and control
ROM.
 Create a control ROM for a different datapath /
instruction set.
 Trace the execution of a program in a pipelined
implementation.
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Students Feedback
 Most students felt…
 they learned a lot when completing the
ANNA programming assignments.
 the ANNA tools were easy to use.
 there was adequate documentation.
 There were several suggestions for
improving the Windows tools:
 line numbers in the assembler
 knowing what addresses labels map to in
the simulator
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Course Outcomes
 Students were asked to judge how well a
particular topic was covered.
 Scale: 1(not covered) to 5 (very well
covered)
 Most topics received a 4.
 No topic received a 2 or lower.
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My Observations
 Using the ANNA assembly language helped
students learn the important concepts.
 No differences between the classes that use the
Windows tools and Linux tools except for
implementing function calls.
 Could be due to improvements in lecture
 ANNA, a simple toy assembly language, did not
dampen student motivation.
 The datapath and design went fairly well.
 Some “hand-waving” at times (pun intended)
 Some students would benefit from having a
textbook.
 Most textbooks are tied to particular language.
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Questions?
More info? Contact me:
Eric Larson
[email protected]
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