System Programming System Software, pp.21-28.

1. System ProgrammingSystem Software, pp.21-28. Chia-Hui Chang, Assistant Professor Dept. of Computer Science & Information Engineering National Central University, Taiwan

2. Traditional (CISC) Machines • Complex Instruction Set Computers (CISC) • complicated instruction set • different instruction formats and lengths • many different addressing modes • e.g. VAX or PDP-11 from DEC • e.g. Intel x86 family • Reduced Instruction Set Computer (RISC)

3. VAX Architecture (1/6) • Virtual Address EXtension • Memory • All addresses are byte address • word (2bytes), longword (4bytes), • quadworad (8bytes), octaword (16bytes) • All VAX programs operate in a virtual address space of 232 bytes • One half is used for system space • The other half is called process space, and is defined for each program

4. VAX Architecture (2/6) • Registers • 16 general purpose registers: R0~R15 • each register is 32-bit long • R15 (PC): Program Counter • R14 (SP): Stack Pointer • R13 (FP): Frame Pointer • R12 (AP): Argument Pointer • R6~R11: general • R0~R5: are used by some instructions • PSL: process status longword

5. VAX Architecture (3/6) • Data Formats • Integers: byte, word, longword, quadword, or octaword • Negative integers: 2’s complement representation • Floating-point: 4~16bytes • packed decimal: (C:positive, D:negative, F:unsigned) • zoned decimal: (digits are represented with ASCII codes) • e.g. +53842, 53842C (packed), 35333834C2 (zoned) • e.g. -6071, 6071D(packed), 363037D1 • numeric format: trailing numeric, leading separate numeric

6. VAX Architecture (4/6) • Instruction Formats • variable -length instruction format • Addressing Modes • register mode • register deferred mode • autoincrement and autodecrement modes • several base relative addressing modes • program-counter relative modes • indirect addressing mode (called deferred modes) • immediate operands

7. VAX Architecture (5/6) • Instruction Set • Goal: symmetric with respect to data type • The instruction mnemonics are formed by • a prefix that specifies the type of operation • a suffix that specifies the data type of the operands • a modifier that gives the number of operands involved • e.g. ADDW2, MULL3, CVTWL • A single instruction for • saves a designated set of registers • passes a list of arguments to the procedure • maintains the stack, frame, and argument pointers • sets a mask to enable error traps for arithmetic operations

8. VAX Architecture (6/6) • Input and Output • I/O device controllers • Each controller has a set of control/status and data registers, which are assigned locations in the physical address space (called I/O space) • No special instructions are required to access registers in I/O space • The association of an address in I/O space with a physical register in a device controller is handled by the memory management routines

9. Pentium Pro Architecture (1/5) • Memory • physical level: byte addresses, word, doubleword • logical level: segments and offsets • In some cases, a segment can also be divided into pages • The segment/offset address specified by the programmer is translated into a physical address by the x86 MMU(Memory Management Unit)

10. Pentium Pro Architecture (2/5) • Registers • General-purpose registers: • EAX, EBX, ECX, EDX: data manipulation • ESI, EDI, EBP, ESP: address • Special-purpose registers: • EIP: next instruction • FLAGS: status word • CS: code segment register • SS: stack segment register • DS, ES, FS, and GS: data segments • Floating-point unit (FPU) • Registers reserved for system programs 16-bit segment registers

11. Pentium Pro Architecture (3/5) • Data Formats • Integers: • 8-, 16-, 32-bit binary numbers • negative values: 2’s complement • FPU can also handle 64-bit signed integers • The least significant part of a numeric value is stored at the lowest-numbered address (little-endian) • binary coded decimal (BCD) • unpacked: 0000____0000____0000____…...0000____ • packed: |____|____|____|____|____|____|…..|____|____| • Floating-point data formats • single-precision: 32 bits=24+7-bit exponent+sign bit • double-precision: 64 bits=53+10-bit exponent+sign bit • extended-precision: 80 bits=64+15-bit exponent+sign bit

12. Pentium Pro Architecture (4/5) • Instruction Formats • prefix (optional) containing flags that modify the operation of instruction • specify repetition count, segment register, etc. • opcode (1 or 2 bytes) • operands and addressing modes • Addressing Modes • TA=(base register)+(index register)*(scale factor)+displacement • base register: any general-purpose registers • index register: any general-purpose registers except ESP • scale factor: 1, 2, 4, 8 • displacement: 8-, 16-, 32- bit value • eight addressing modes

13. Pentium Pro Architecture (5/5) • Instruction Set • 400 different machine instructions • R-to-R instructions, R-to-M instructions, M-to-M instructions • immediate values, • special purpose instructions for high-level programming language • entering and leaving procedures, • checking subscript values against the bounds of an array • Input and Output • Input is performed by instructions that transfer one byte, word, or doubleword from an I/O register EAX • Repetition prefixes allow these instructions to transfer an entire string in a single operation