1 CS232: Computer Architecture II Fall 2011 Intel i7 Quad-core

2 Who we are  Lecturer: Prof. Craig  Teaching Assistants/Section Instructor: Room 0212 SC Ryan Cunninghamnoon section Dwight Guth3pm section Charles Tucker1pm section  —MP 1 released on Thursday, due next Thursday. Make sure you have an EWS account!

3  Computer architecture is about building and analyzing computer systems  Instruction Set Architecture is bridge between hardware and software —Study the MIPS ISA in detail —Learn what compilers do when they translate high-level code into assembly (we won’t learn how they do it) —Learn how HLL program constructs are represented to the machine  Key techniques: Pipelining, Caching, Virtual Memory  Tuning complex code for performance  Hardware support for parallelism What is computer architecture about? Memory Processor Input/Output Compiler HLLASM

4  The ISA is an interface between software and hardware —the hardware “promises” to implement all ISA instructions —the software uses ISA primitives to build complex programs  Later in the semester, we’ll see how the ISA affects the hardware design Instruction set architectures Software Hardware ISA

5  We study the MIPS instruction set architecture to illustrate concepts in assembly language and machine organization —concepts are not MIPS-specific —MIPS is just convenient because it is real, yet simple (unlike x86)  MIPS ISA is used in many places, primarily in embedded systems —routers from CiscoCisco —game machines like the Nintendo 64 and Sony Playstation 2 & PSPNintendo 64Sony Playstation 2 Why MIPS?

6 What you will need to learn for Exam 1  You must become “fluent” in MIPS assembly: —Translate from C++ to MIPS and MIPS to C++  Example: Translate the following recursive C++ function into MIPS int pow(int n, int m) { if (m == 1) return n; return n * pow(n, m-1); } How are arguments passed? How are values returned? How are complex expressions broken into simple instructions? How is recursion done?

7 MIPS: register-to-register, three address  MIPS is a register-to-register, or load/store, architecture —destination and sources of instructions must all be registers —special instructions to access main memory (later)  MIPS uses three-address instructions for data manipulation —each ALU instruction contains a destination and two sources  For example, an addition instruction (a = b + c) has the form: add a, b, c operation destinationsources operands

8 MIPS register file  MIPS processors have 32 registers, each of which holds a 32-bit value —register addresses are 5 bits long  More registers might seem better, but there is a limit to the goodness: —more expensive: because of registers themselves, plus extra hardware like muxes to select individual registers —instruction lengths may be affected D data Write D address A addressB address A dataB data 32  32 Register File

9 MIPS register names  MIPS register names begin with a $. There are two naming conventions: —by number: $0 $1 $2 … $31 —by (mostly) two-character names, such as: $a0-$a3 $s0-$s7 $t0-$t9 $sp $ra  Not all of the registers are equivalent: —e.g., register $0 or $zero always contains the value 0 —some have special uses, by convention ( $sp holds “stack pointer”)  You have to be a little careful in picking registers for your programs —for now, stick to the registers $t0-$t9

10 Basic arithmetic and logic operations  The basic integer arithmetic operations include the following: add sub mul div  And here are a few bitwise operations: and or xor nor  Remember that these all require three register operands; for example: add $t0, $t1, $t2# $t0 = $t1 + $t2 mul$s1, $s1, $a0# $s1 = $s1 x $a0 Note: a full MIPS ISA reference can be found in Appendix A (linked from website)

11  Complex arithmetic expressions may require multiple MIPS operations  Example: t0  (t1  t2)  (t3  t4) add$t0, $t1, $t2# $t0 contains $t1 + $t2 sub$t6, $t3, $t4# temp value $t6 = $t3 - $t4 mul$t0, $t0, $t6# $t0 contains the final product  Temporary registers may be necessary, since each MIPS instructions can access only two source registers and one destination —in this example, we could re-use $t3 instead of introducing $t6 —must be careful not to modify registers that are needed again later Larger expressions

12 How are registers initialized?  Special MIPS instructions allow you to specify a signed constant, or “immediate” value, for the second source instead of a register —e.g., here is the immediate add instruction, addi: addi $t0, $t1, 4# $t0 = $t1 + 4  Immediate operands can be used in conjunction with the $zero register to write constants into registers: addi $t0, $0, 4# $t0 = 4 Shorthand: li $t0, 4# $t0 = 4 (pseudo-instruction)

13 Our first MIPS program  Let’s translate the following C++ program into MIPS: void main() { int i = 516; int j = i*(i+1)/2; i = i + j; } main: # start of main li $t0, 516 # i = 516 addi $t1, $t0, 1 # i + 1 mul $t1, $t0, $t1 # i * (i + 1) li $t2, 2 div $t1, $t1, $t2 # j = i*(i+1)/2 add $t0, $t0, $t1 # i = i + j jr $ra # return