ENGR 330: Today’s Class

ENGR 330: Today’s Class • Exam Topic Overview • Technical Topic Review • Skills Review – conversions, programming • Data: Characters • Data: Floating Point R. Smith - University of St Thomas - Minnesota

Topics for the Exam • Data Formats: convert to/from decimal • Sign and magnitude, 1’s complement, 2’s complement • 2’s 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 we’ve studied • Stacks and Method Calls • Role of different MIPS registers • “Program wide” and “per method” memory maps R. Smith - University of St Thomas - Minnesota

Suggestions • Print out copies of lecture notes • They should fit readably 6 to a page • You probably don’t need to print out the lecture with all the instruction data flows • If you don’t “get” instruction data flows, don’t worry, we’ll be doing a lot of that in the next few weeks • It’s easier to use the appendix in P&P 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 R. Smith - University of St Thomas - Minnesota

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 – what’s different in the ISA between them R. Smith - University of St Thomas - Minnesota

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 R. Smith - University of St Thomas - Minnesota

“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 R. Smith - University of St Thomas - Minnesota

Skills Review • Representation/Conversion • 2’s 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 R. Smith - University of St Thomas - Minnesota

“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? R. Smith - University of St Thomas - Minnesota

Characters • Comparison issues • 3 vs ‘3’ vs “3” • Character (decimal) to integer conversion R. Smith - University of St Thomas - Minnesota

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 R. Smith - University of St Thomas - Minnesota

Floating Point Format • First bit is the sign • Easy to compare <0 or >0 • Next is exponent • Easier to compare magnitude of numbers based on exponent • EXCEPT that negative exponents are “larger” than positive • Exponent in 2’s complement notation • Finally comes the mantissa • Generally a ‘hidden’ 1 at the top – implicitly always there • Unsigned magnitude value • “Sign and magnitude” form R. Smith - University of St Thomas - Minnesota

ENGR 330: Today’s Class