ENGR 330: Todays Class

1
ENGR 330 Todays Class

• Exam Topic Overview
• Technical Topic Review
• Skills Review conversions, programming
• Data Characters
• Data Floating Point

2
Topics for the Exam

• Data Formats convert to/from decimal
• Sign and magnitude, 1s complement, 2s
  complement
• 2s complement binary and hex arithmetic
• AND, OR, NOT, Add, Subtract
• Programming
• Arithmetic expressions for MIPS or LC-3
• Conditionals (IFs) in LC-3 assembly language
• Looping in LC-3 assembly language
• Instruction Set Architectures
• Properties compare for processors weve studied
• Stacks and Method Calls
• Role of different MIPS registers
• Program wide and per method memory maps

3
Suggestions

• Print out copies of lecture notes
• They should fit readably 6 to a page
• You probably dont need to print out the lecture
  with all the instruction data flows
• If you dont get instruction data flows, dont
  worry, well be doing a lot of that in the next
  few weeks
• Its easier to use the appendix in PP that
  describes how the instructions work
• Bring BOTH books on Monday, just to be safe
• It should be enough to just bring the little MIPS
  card if you feel comfortable with how MIPS
  instructions work

4
Properties of ISAs

• Data sizes for operations (register sizes)
• Address range for RAM
• Common address modes for RAM
• Which types of instructions use which modes
• EX fetch store design vs. allowing arithmetic
  to access RAM
• Instruction Sizing
• Fixed vs variable length instructions
• Things to Look For
• Shared consistencies things both processors do
• Differences whats different in the ISA between
  them

5
Memory Maps and Methods

• Global map for a running program
• Text
• Data region
• Starts with fixed global data
• Then comes a variable sized heap of data given
  to the program piecemeal on request
• Stack

6
Map for individual methods

• Section 2.7 Stacks and Methods
• Described in terms of MIPS subroutine calls
• Stack Frame
• Return address
• Local variables for the new method
• Pointed to by Frame Pointer
• Registers saved while used locally
• Stack Pointer start of RAM belonging to the
  stack
• Stack grows downward in RAM as more space is
  needed
• Must ALWAYS pop the stack back to its starting
  point when done with it like when a method is
  finished and returns to its caller

7
Skills Review

• Representation/Conversion
• 2s Complement add/subtract
• Binary/hex add, subtract, and, or, not
• Arithmetic in LC-3 or MIPS
• Short RAM example
• Longer register based example
• IF example in LC-3
• Min/max using registers
• Loop example
• Down counting
• Sentinel value

8
The assignment that got away

• Write a MIPS program that adds a list of 4 or 8
  integers and calculates the (truncated) average
  value. Do NOT use the built-in Divide operation.
• How do you calculate the average?
• How do you do it without integer divide?

9
Characters

• Comparison issues
• 3 vs 3 vs 3
• Character (decimal) to integer conversion

10
What is Floating Point?

• Parts
• Mantissa the fraction part
• Exponent powers of 2
• Signs
• Special Values 0, Infinity, and Not a Number
• Problems
• Overflow, Underflow
• Loss of precision
• Double vs Float
• Float 32 bits, 8 bit exponent, 23 bit mantissa,
  sign bit
• Double 64 bits, 11 bit exponent, 52 bit
  mantissa, sign bit

11
Floating Point Format

• First bit is the sign
• Easy to compare lt0 or gt0
• Next is exponent
• Easier to compare magnitude of numbers based on
  exponent
• EXCEPT that negative exponents are larger than
  positive
• Exponent in 2s complement notation
• Finally comes the mantissa
• Generally a hidden 1 at the top implicitly
  always there
• Unsigned magnitude value
• Sign and magnitude form