CPU organization in computer organization

1. Chapter-1
Basic Structure of Computers

2. CPU Organization
• Study of design and architecture of a small accumulator based CPU,
• A typical CPU with general register organization,
• Pipelining,
• Functional units,
• Floating-Point numbers, Addressing modes,
• Accessing I/O devices,
• Linker, Compiler, Debugger

3. Fundamentals:
• Function of CPU: To execute sequence of instructions
• Program execution

5. Cache Memory:
• Extremely fast and small memory
• Placed between CPU and main memory
• Used for temporarily storing data

6. Small accumulator
based CPU:

7. Architecture extensions:
• Multipurpose register set for storing data and addresses(register file)
• Additional data, instructions and address types
• Register to indicate computation status (Status Register)
• Program control stack
-Stack Pointer keeps track of stacks entry point
-A part of external mem is used as push down stack mem

8. A typical CPU with
general register
organization:

9. Pipelining:
• Parallelism may be present in DPU, overlapping carried out by DPU or
PCU
• "A pipeline processor consists of a sequence of processing circuits,
called segments or stages, through which a stream of operands can
be passed.
• "Partial processing of the operands takes place in each segment.
• "... a fully processed result is obtained only after an operand set has
passed through the entire pipeline."

10. Pipelining:
• A Pipeline is a series of stages, where some work is done at each
stage. The work is not finished until it has passed through all stages.
• Types of Pipelines
• Instructional pipeline
where different stages of an instruction fetch and execution are
handled in a pipeline.
• Arithmetic pipeline
where different stages of an arithmetic operation are handled
along the stages of a pipeline.

11. Basic Information Types

12. Fixed- Point Numbers
• Allows limited range of values and have relatively simple hardware
requirements
• Binary Numbers:
-derived from ordinary representation of number
-left side represent number while right side represent fraction
called positional notation(each digit has same weight)
• Decimal Numbers- use of BCD
• Hexadecimal Numbers

13. Floating- Point Numbers
• Allows much larger range of values but require either costly processing
hardware or lengthy software implementations
• Floating point codes used in computers are binary(or binary coded) version
• 3 numbers associated with floating point number-
M (Mantissa),
E (Exponent),
B (Base)

14. Instruction Set
• Instruction Format
• Combination of opcode and operand
op X1, X2,X3,…….,Xn ADD A, B
• RISC Format

15. Addressing Modes
• To point the current value V(X) of some operand X used by an instruction
1. Immediate Addressing modes MOV R0, #300-opernd is mentioned
directly
2. Direct Addressing modes
MOV R0, X
3. Indirect Addressing modes MOV R0, (P) //p contains address of x
4. Relative Addressing modes MOV R0, 30
used without modifications, requires complete operand address

16. Accessing I/O Devices
• The interconnection network consists of circuits
needed to transfer information between the
processor, the memory unit, and a number of I/O
devices.
• Load and Store instructions use addressing modes to
generate effective addresses that identify the desired
locations.
• Each I/O device must appear to the processor as consisting of some
addressable locations, just like the memory.
• The I/O devices and the memory share the same address space, this
arrangement is called memory-mapped I/O.
• Load R2, DATAIN
• Store R2, DATAOUT

17. Linker
• All instructions and data for a particular program are specified in a single
source file from which the assembler generates an object program
• Each program may contain references to external names, which are address
labels defined in other source files.
• A utility program called the linker is used to combine the contents of separate
object files into one object program.
• The linker needs the relative positions of address labels defined in the source
files.
• The linker uses the information in each object file and the known sizes of
machine language programs to build a memory map of the final combined
object file.

18. Compiler
• A utility program called a compiler performs the first task.
• A source file in a high-level language is prepared by the programmer and stored
on the disk.
• The compiler generates assembly-language instructions and directives, and
writes them into an output file.
• It is often convenient to partition a high-level source program into multiple files,
grouping subroutines together based on related tasks.
• For each source file, the compiler generates an assembly-language file, then
invokes the assembler to generate an object file.
• Benefit of programming in a high-level language is that the compiler automates
many of the tedious tasks that a programmer has to do when programming in
assembly language

19. Compiler Optimizations
• Improved performance can be achieved if the compiler uses techniques
such as reordering the instructions produced from a straightforward
approach.
• A compiler with such capabilities is called an optimizing compiler.
• Because much of the execution time of a program is spent in loops,
compilers may apply optimizations that are particularly effective for loops.

20. Debugger
• An object program is generated successfully when there are no syntax errors
or unknown names in the source files for the program.
• When an object program is executed, it may produce incorrect results due to
programming errors, or bugs, that are often difficult to isolate.
• To help the programmer identify such errors, a utility program called the
debugger can be used.
• It enables the programmer to stop execution of the object program at some
points of interest and to examine the contents of various processor registers
and memory locations.
• the programmer can compare computed values with the expected results at
any point of
• execution to determine where a programming error may exist.

21. Debugger
• Trace Mode:
• When a processor is operating in the trace mode, an interrupt occurs
after the execution of every instruction.
• When the user enters a command to resume execution of the object
program, a return from- interrupt instruction is executed.
• The next instruction in the program being debugged is executed, then the
debugger is activated again with another interrupt.
• The trace-mode interrupt is automatically disabled when the debugger
routine is entered, and re-enabled upon return to the object program.

22. Debugger
• Breakpoints:
• Breakpoints provide a similar interrupt-based debugging facility, except
that the object program being debugged is interrupted only at specific
points indicated by the programmer.
• The programmer may set a breakpoint to determine whether a particular
subroutine in the object program is ever reached.
• The advantage of using a breakpoint is that execution proceeds at full
speed until the breakpoint is encountered.
• A special instruction called Trap or Software-interrupt is usually used to
implement breakpoints.