Chapter 4 Processor

Harvard Architecture
4 components: processor, instruction memory, data memory, and I/O facilities

advantages:
one memory unit optimized to store programs and another memory unit optimized to store data.
disadvantages: inflexibility

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Von Neumann Architecture

Von Neumann Architecture offers complete flexibility.

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4 categories of processor:

fixed logic : sin(x)
selectable logic : sin(x), cos(x)
parameterized logic : hash function
programmable logic :

Graphics engine
Graphics engines, sometimes called graphics accelerators, are common because video game software is popular and many computers need a graphics engine to drive the graphics display at high speed. For example, a graphics engine might include facilities to repaint the surface of a graphical figure after it has been moved.

Structure of A Conventional Processor
Controller
Arithmetic Logic Unit (ALU)
Local data storage (typically, registers)
Internal interconnection(s)
External interface(s) (I/O buses)

Processor Categories and Roles
Coprocessors
Microcontrollers
Embedded system processors
General-purpose processors

Coprocessors. Usually, a coprocessor consists of a special-purpose processor that performs a single task at high speed. For example, a floating point accelerator.

Microcontrollers. For example, microcontrollers run physical systems such as the engine in a modern automobile, the landing gear on an airplane, and the automatic door in a grocery store.

Embedded system processors. The processors used for embedded systems are usually more powerful than the processors that are used as microcontrollers, and often run a protocol stack used for communication.

Program translation

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We will see later that operations involving memory access or I/O can require significantly more time (i.e., more clock cycles) than those that do not.

Starting the Fetch-Execute Cycle

How does a processor start the fetch-execute cycle? The answer is complex because it depends on the underlying hardware. For example, some processors have a hardware reset. When voltage is removed from the reset line, the processor begins executing a program from a fixed location. Some processors start executing a program found at location zero in memory once the processor is reset. In such systems, the designer must guarantee that a valid program is placed in location zero before the processor starts.

The steps used to start a processor are known as a bootstrap. On a conventional computer, the hardware reads a copy of the operating system from an I/O device, such as a disk, and places the copy into memory before starting the processor.

Many devices have a soft power switch, which means that the power switch does not actually turn power on or off. Instead, the switch acts like a sensor — the processor can interrogate the switch to determine its current position. When power is first applied, the processor boots to an initial state. The initial state consists of a loop that interrogates the soft power switch. Once the user presses the soft power switch, the hardware completes the bootstrap process.