1. Assembly Language for Intel-Based Computers Chapter 2: IA-32 Processor Architecture Kip Irvine

2. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 2 General Concepts Basic microcomputer design Instruction execution cycle Reading from memory

3. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 3 Basic Microcomputer Design clock synchronizes CPU operations control unit (CU) coordinates sequence of execution steps ALU performs arithmetic and bitwise processing

4. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 4 Clock synchronizes all CPU and BUS operations machine (clock) cycle measures time of a single operation clock is used to trigger events

5. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 5 Instruction Execution Cycle Fetch Decode Fetch operands Execute Store output

6. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 6 Multi-Stage Pipeline Instruction execution divided into discrete stages Example of a non- pipelined processor. Many wasted cycles.

7. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 7 Pipelined Execution More efficient use of cycles, greater throughput of instructions: For k states and n instructions, the number of required cycles is: k + (n – 1)

8. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 8 Reading from Memory Multiple machine cycles are required when reading from memory, because it responds much more slowly than the CPU. The steps are: address placed on address bus Read Line (RD) set low CPU waits one cycle for memory to respond Read Line (RD) goes to 1, indicating that the data is on the data bus

9. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 9 Basic Execution Environment Addressable memory General-purpose registers Index and base registers Specialized register uses Status flags Floating-point

10. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 10 General-Purpose Registers Named storage locations inside the CPU, optimized for speed.

11. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 11 Accessing Parts of Registers Use 8-bit name, 16-bit name, or 32-bit name Applies to EAX, EBX, ECX, and EDX

12. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 12 Index and Base Registers Some registers have only a 16-bit name for their lower half:

13. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 13 Some Specialized Register Uses (1 of 2) General-Purpose EAX – accumulator ECX – loop counter ESP – stack pointer ESI, EDI – index registers EBP – extended frame pointer Segment CS – code segment DS – data segment SS – stack segment ES, FS, GS - additional segments

14. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 14 Some Specialized Register Uses (2 of 2) EIP – instruction pointer EFLAGS status and control flags each flag is a single binary bit

15. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 15 Status Flags Carry unsigned arithmetic out of range Overflow signed arithmetic out of range Sign result is negative Zero result is zero Auxiliary Carry carry from bit 3 to bit 4 Parity sum of 1 bits is an even number

16. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 16 Carry and Overflow Carry is important when … Adding or subtracting unsigned integers Indicates that the unsigned sum is out of range Overflow is important when … Adding or subtracting signed integers Indicates that the signed sum is out of range Overflow occurs when Adding two positive numbers and the sum is negative Adding two negative numbers and the sum is positive Can happen because of the fixed number of sum bits

17. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 17 01000000 01001111 + 10001111 79 64 143 (-113) Carry = 0 Overflow = 1 1 10011101 11011010 + 01110111 218 (-38) 157 (-99) 119 Carry = 1 Overflow = 1 111 Carry and Overflow Examples We can have carry without overflow and vice-versa Four cases are possible 00001000 00001111 + 00010111 15 8 23 Carry = 0 Overflow = 0 1 11110101 00001111 + 00000 1 00 15 245 (-11) 4 Carry = 1 Overflow = 0 11111 1

18. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 18 Addressable Memory Protected mode 4 GB 32-bit address Real-address and Virtual-8086 modes 1 MB space 20-bit address

19. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 19 Real-Address mode 1 MB RAM maximum addressable Application programs can access any area of memory Single tasking Supported by MS-DOS operating system

20. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 20 Segmented Memory Segmented memory addressing: absolute (linear) address is a combination of a 16-bit segment value added to a 16-bit offset linear addresses one segment

21. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 21 Calculating Linear Addresses Given a segment address, multiply it by 16 (add a hexadecimal zero), and add it to the offset Example: convert 08F1:0100 to a linear address Adjusted Segment value: 0 8 F 1 0 Add the offset: 0 1 0 0 Linear address: 0 9 0 1 0

22. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 22 Calculating Linear Addresses What linear address corresponds to the segment/offset address 028F:0030? 028F0 + 0030 = 02920 Always use hexadecimal notation for addresses.

23. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 23 Calculating Linear Addresses What segment addresses correspond to the linear address 28F30h? Many different segment-offset addresses can produce the linear address 28F30h. For example: 28F0:0030, 28F3:0000, 28B0:0430,...

24. Web siteWeb site ExamplesExamples Irvine, Kip R. Assembly Language for Intel-Based Computers 5/e, 2007. 24 Intel Registers