4-1 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Computer Architecture and Organization Miles Murdocca and Vincent Heuring Chapter 4 – The Instruction Set Architecture

4-2 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Chapter Contents 4.1 Hardware Components of the Instruction Set Architecture 4.2 ARC, A RISC Computer 4.3 Pseudo-Operations 4.4 Synthetic Instructions 4.5 Examples of Assembly Language Programs 4.6 Accessing Data in Memory—Addressing Modes 4.7 Subroutine Linkage and Stacks 4.8 Input and Output in Assembly Language 4.9 Case Study: The Java Virtual Machine ISA

4-3 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring The Instruction Set Architecture The Instruction Set Architecture (ISA) view of a machine corresponds to the machine and assembly language levels. A compiler translates a high level language, which is architecture independent, into assembly language, which is architecture dependent. An assembler translates assembly language programs into executable binary codes. For fully compiled languages like C and Fortran, the binary codes are executed directly by the target machine. Java stops the translation at the byte code level. The Java virtual machine, which is at the assembly language level, interprets the byte codes (hardware implementations of the JVM also exist, in which Java byte codes are executed directly.)

4-4 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring The System Bus Model of a Computer System, Revisited A compiled program is copied from a hard disk to the memory. The CPU reads instructions and data from the memory, executes the instructions, and stores the results back into the memory.

4-5 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Common Data Type Sizes A byte is composed of 8 bits. Two nibbles make up a byte. Halfwords, words, doublewords, and quadwords are composed of bytes as shown below:

4-6 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Big-Endian and Little-Endian Formats In a byte-addressable machine, the smallest datum that can be referenced in memory is the byte. Multi-byte words are stored as a sequence of bytes, in which the address of the multi-byte word is the same as the byte of the word that has the lowest address. When multi-byte words are used, two choices for the order in which the bytes are stored in memory are: most significant byte at lowest address, referred to as big-endian, or least significant byte stored at lowest address, referred to as little-endian.

4-7 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Memory Map for the ARC Memory locations are arranged linearly in consecutive order. Each numbered location corresponds to an ARC word. The unique number that identifies each word is referred to as its address.

4-8 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Example of ARC Memory Layout The table illustrates both the distinction between an address and the data that is stored there, and the fact that ARC/SPARC is a big-endian machine. The table shows four bytes stored at consecutive addresses to Thus the byte address 0x contains the byte 0xDD. Since this is a big-endian machine (the big end is stored at the lowest address) the word stored at address 0x is 0xAABBCCDD.

4-9 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Abstract View of a CPU The CPU consists of a data section containing registers and an ALU, and a control section, which interprets instructions and effects register transfers. The data section is also known as the datapath.

4-10 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring The Fetch-Execute Cycle The steps that the control unit carries out in executing a program are: (1) Fetch the next instruction to be executed from memory. (2) Decode the opcode. (3) Read operand(s) from main memory, if any. (4) Execute the instruction and store results, if any. (5) Go to step 1. This is known as the fetch-execute cycle.

4-11 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring An Example Datapath The ARC datapath is made up of a collection of registers known as the register file and the arithmetic and logic unit (ALU).

4-12 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring ARC User-Visible Registers

4-13 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring ARC Assembly Language Format The ARC assembly language format is the same as the SPARC assembly language format. This example shows the assembly language format for ARC (and SPARC) arithmetic and logic instructions.

4-14 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring ARC Load / Store Format This example shows the assembly language format for ARC load and store instructions.

4-15 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Simple Example: Add Two Numbers The figure shows a simple program fragment using our ld, st, and add instructions. This fragment is equivalent to the C statement: z = x + y; Since ARC is a load-store machine, the code must first fetch the x and y operands from memory using ld instructions, and then perform the addition, and then store the result back into z using an st instruction.

4-16 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring ARC Transfer of Control Sequence This example shows the assembly language format for ARC branch instructions.

4-17 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring ARC Fragment that Computes the Absolute Value As an example of using the ARC instruction types we have seen so far, consider the absolute value function, abs: abs(x) := if (x < 0) then x = -x; An ARC fragment to implement this is shown below:

4-18 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring A Portion of the ARC ISA The ARC ISA is a subset of the SPARC ISA. A portion of the ARC ISA is shown here.

4-19 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring ARC Instruction and PSR Formats

4-20 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring ARC Data Formats

4-21 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring ARC Pseudo-Ops Pseudo-ops are instructions to the assembler. They are not part of the ISA, but instruct the assembler to do an operation at assembly time.

4-22 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Synthetic Instructions Many assemblers will accept synthetic instructions that are converted to actual machine-language instructions during assembly. The figure below shows some commonly used synthetic instructions. Synthetic instructions are single instructions that replace single instructions, which are different from macros which are discussed later.

4-23 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring ARC Example Program An ARC assembly language program adds two integers:

4-24 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring A More Complex Example Program An ARC program sums five integers.

4-25 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring One, Two, Three-Address Machines Consider how the C expression A = B*C + D might be evaluated by each of the one, two, and three-address instruction types. Assumptions: Addresses and data words are two bytes in size. Opcodes are 1 byte in size. Operands are moved to and from memory one word (two bytes) at a time. Three-Address Instructions: In a three-address instruction, the expression A = B*C + D might be coded as: multB, C, A addD, A, A which means multiply B by C and store the result at A. (The mult and add operations are generic; they are not ARC instructions.) Then, add D to A and store the result at address A. The program size is 7  2 = 14 bytes. Memory traffic is  (2  3) = 26 bytes.

4-26 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring One, Two, Three-Address Machines Two Address Instructions: In a two-address instruction, one of the operands is overwritten by the result. Here, the code for the expression A = B*C + D is: loadB, A multC, A addD, A The program size is now 3  (1+2  2) or 15 bytes. Memory traffic is   2  3 or 31 bytes.

4-27 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring One, Two, Three-Address Machines One Address (Accumulator) Instructions: A one-address instruction employs a single arithmetic register in the CPU, known as the accumulator. The code for the expression A = B*C + D is now: load B multC addD storeA The load instruction loads B into the accumulator, mult multiplies C by the accumulator and stores the result in the accumulator, and add does the corresponding addition. The store instruction stores the accumulator in A. The program size is now 3  4 or 12 bytes, and memory traffic is  2 or 20 bytes.

4-28 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Addressing Modes Four ways of computing the address of a value in memory: (1) a constant value known at assembly time, (2) the contents of a register, (3) the sum of two registers, (4) the sum of a register and a constant. The table gives names to these and other addressing modes.

4-29 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Subroutine Linkage – Registers Subroutine linkage with registers passes parameters in registers.

4-30 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Subroutine Linkage – Data Link Area Subroutine linkage with a data link area passes parameters in a separate area in memory. The address of the memory area is passed in a register (%r5 here).

4-31 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Subroutine Linkage – Stack Subroutine linkage with a stack passes parameters on a stack.

4-32 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Stack Linkage Example A C program illustrates nested function calls.

4-33 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Stack Linkage Example (cont’) (a-f) Stack behavior during execution of the program shown in previous slide.

4-34 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Stack Linkage Example (cont’) (g-k) Stack behavior during execution of the C program shown previously.

4-35 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Input and Output for the ISA Memory map for the ARC, showing memory mapped I/O.

4-36 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Touchscreen I/O Device A user selecting an object on a touchscreen:

4-37 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Flowchart for I/O Device Flowchart illustrating the control structure of a program that tracks a touchscreen.

4-38 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Java Virtual Machine Architecture

4-39 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Java Pro- gram and Com- piled Class File

4-40 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring A Java Class File

4-41 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring A Java Class File (Cont’)

4-42 Chapter 4 - The Instruction Set Architecture Computer Architecture and Organization by M. Murdocca and V. Heuring © 2007 M. Murdocca and V. Heuring Byte Code for Java Program Disassembled byte code for previous Java program. LocationCodeMnemonicMeaning 0x00e30x10bipushPush next byte onto stack 0x00e40x0f15Argument to bipush 0x00e50x3cistore_1Pop stack to local variable 1 0x00e60x10bipushPush next byte onto stack 0x00e70x099Argument to bipush 0x00e80x3distore_2Pop stack to local variable 2 0x00e90x03iconst_0Push 0 onto stack 0x00ea0x3eistore_3Pop stack to local variable 3 0x00eb0x1biload_1Push local variable 1 onto stack 0x00ec0x1ciload_2Push local variable 2 onto stack 0x00ed0x60iaddAdd top two stack elements 0x00ee0x3eistore_3Pop stack to local variable 3 0x00ef0xb1returnReturn