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Report on "Chapter 4: Bus-Based Computer Systems"

INTRODUCTION:

The microprocessor is an important element of the embedded computing system, but it cannot do its job

without memories and I/O devices. We need to understand how to interconnect microprocessors and devicesusing the CPU bus.

What is the Bus?

Mechanism by which the CPU communicates with memory and devices.

Collection of wires that defines a protocol by which the CPU, memory, and

devices communicate.

Protocols controls the communications between devices

Examples: SPI, I 2 C, USB, UART, etc

Timing diagrams:

Specify the behavior of the bus and the system. Shows how the signals on the bus vary over the time.

Timing Constraints: Make sure that signals go to their proper values at proper time.

Bus multiplexing: Multiplexed address/ data Reduces # of wires (share the same lines).

Direct memory access (DMA): Direct memory access (DMA) is a bus operation that allows reads and writes

not controlled by the CPU. A DMA transfer is controlled by a DMA

controller, which requests control of the bus from the CPU. After

gaining control, the DMA controller performs read and write

operations directly between devices and memory.

System Bus Configurations: A microprocessor system often has more

than one bus.

High-speed devices >> connected to a high-performance bus

Lower-speed devices >> connected to a different bus

Bridge: Allows the buses to connect to each other, Serves as a protocol translator between the two bridges as

well.

ARM AMBA bus: Advanced Microcontroller/or Microprocessor Bus Architecture

is an open standard, on-chip interconnect specification for the connection and management of functional

blocks in a (SoC).

AHB supports pipelining, burst transfers, split transactions, multiple bus masters.

All devices are slaves on APB. (To be able to control the operations)

Memory Device Organization

Several different types of memory: DRAM, SRAM, Flash, ROM.

Each type of memory comes in varying: Capacities, Widths.

Random-access memory: Dynamic RAM is dense, requires refresh.

Synchronous DRAM is dominant type.

SDRAM uses clock to improve performance, pipeline memory accesses.

Static RAM is faster, less dense, consumes more power.

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I/O DEVICES

Timers and Counters: Commonly used in embedded computing systems

A timer is incremented by a periodic signal;

A counter is incremented by an asynchronous, occasional signal.

Watchdog timer: Watchdog timer is periodically reset by system timer, If watchdog is not reset, it generatesan interrupt to reset the CPU.

ADC and DAC conversion: Often used to interface non-digital devices to embedded systems.

COMPONENT INTERFACING: Building the logic to interface a device to a bus is not too difficult. Determine

your components, Read datasheets, Study Application notes,

make a sample board for testing.

System architectures: Architectures and components:

Software: (Compiler, assembler, Instruction sets, etc.)

Hardware: (CPU, bus, memory, I/O devices, etc.)

Some software is very hardware-dependent. Hardware and software architectures:

Hardware design: we can do this in two levels with different

methods: Board level, I/O devices level.

The PC as a platform: For low-volume applications and environments such as factories and offices

where size and power are not critical, we use a PC to build an embedded system.

Typical busses: - PCI: standard for high-speed interfacing 33 or 66 MHz,

- USB (Universal Serial Bus), Fire-wire (IEEE 1394): relatively low-cost serial interface with high speed.Development Environments:The Embedded System software development on a PC known as a host-Use

a host system to prepare software for target system.The host and target are connected by a USB link (or

other links)

Cross compiler: compiles code on host for target system.

Cross debugger: displays target state, allows target system to be controlled.Debugging Techniques: Debugging by software is a monitor program residing on the target provides

basic debugger functions. A common debugging tool is the breakpoint technique; it can be achieved by

modifying some instructions with an instruction that calls the monitoring program, so user can stop

execution of the program, examine system state, and/or change states before continuing execution.

In-circuit emulators: A microprocessor in-circuit emulator is a specially-instrumented microprocessor, Allows

you to stop execution, examine CPU state, modify registers. It is a specialized hardware tool that can help

debug software in a working embedded system.Debugging Techniques Challenges:

target system may be hard to observe; target may be hard to control; may be hard to generate realistic inputs; Setup sequence may be complex.System- Level performance analysis: we must take in account the effect of all system elements on the

performance like CPU, buses, Memory and I/O devices.