Software Layers and Firmware

• The software controls the operation and functionality of the computer
• There are many "layers" of software in the computer

Software Layers

• Desktop computers have layers of applications, operating systems, firmware, and hardware.
• Complex embedded computers also have these same layers.
• Simple embedded computers have application, firmware, and hardware layers.

Firmware

• Firmware is a piece of software that directly controls the hardware.
• Firmware is often referred to as low-level software.

Devices with Firmware

• In computers, BIOS or UEFI firmware manages hardware initialization during the boot process.
• In smartphones, firmware controls touchscreens, cameras, and modems.
• Home appliances (microwaves, washing machines, and TVs) use firmware for operation.
• Embedded Systems like car control systems, IoT devices, and medical equipment depend heavily on firmware.

Computer System Components

• Computer systems consist of three main components.
• The Central Processing Unit (CPU), also called the microprocessor, coordinates all activities within a computer.
• Memory stores program instructions and data.
• Input/Output (I/O) Devices allow the computer to input information for processing and output the results; they are also known as computer peripherals.
• The integrated circuit chip containing the CPU is called the microprocessor.
• A microcomputer is a relatively smaller computer with a CPU as a microprocessor, typically used as a personal computer (PC) which is smaller than a mainframe computer.

Computer Block Diagram

• A computer's architecture includes input devices (keyboard, mouse, microphone), a CPU (with control unit, ALU, registers, and cache memory), primary memory unit, secondary/auxiliary memory (HDD, SSD), output devices (monitor, speaker, printer), a power supply, and a cooling fan.

Busses

• The CPU connects to memory and I/O devices through a bus.
• The bus inside a computer carries information.
• There are three types of busses: address, data, and control.
• The address bus identifies the memory location or I/O device the processor intends to communicate with.
• The data bus is used by the CPU to get data from and send data to memory or I/O devices, which is used to classify the microprocessor.
• The data bus size of Intel microprocessors vary between 8-bit (8085) to 64-bit (Pentium).
• The control bus determines if the address on the bus is a memory address or an I/O device address, activating control bus signals.
• Control bus signals include Memory Read, Memory Write, I/O Read, and I/O Write.
• Address and control busses contain output lines only; therefore, they are unidirectional.
• The data bus is bidirectional.

Address Bus

• When a CPU executes an instruction like LOAD R1, [0x0010], the address bus sends the address 0x0010 to the memory controller, indicating the memory location to retrieve data.
• In a microcontroller, the address bus carries the address of an I/O device for register access.

Data Bus

• When executing LOAD R1, [0x2000], the CPU places the memory address 0x2000 on the address bus.
• The address is sent to the memory controller to specify any memory location.
• The CPU sends a read signal on the control bus.
• The memory controller retrieves the data stored at address 0x2000.
• The retrieved data (e.g., the byte 0x7F) is placed on the data bus by the memory controller.
• The CPU reads this data from the data bus and stores it in register R1.

Memory

• Microcomputers use two types of memory.
• RAM (Random Access Memory/Read-Write Memory) is used for temporary storage of running programs, and data is lost when the computer is turned off, known as volatile memory.
• ROM (Read Only Memory) stores permanent information that is not lost when the power is off, called nonvolatile memory.
• RAM is primary storage, and magnetic/optical disks are secondary storage.

Inside the CPU

• A program stored in the memory provides instructions to the CPU to perform a specific action, which is function of the CPU.
• The CPU contains registers to store information temporarily, which can be 8-bit, 16-bit, 32-bit or 64-bit depending on the CPU.
• The CPU contains an Arithmetic and Logic Unit (ALU) to perform arithmetic (add, subtract, multiply, divide) and logic (AND, OR, NOT) functions.
• The CPU contains a program counter, also known as the Instruction Pointer, to point to the address of the next instruction to be executed.
• The Instruction Decoder interprets the meaning of the instruction fetched into the CPU by the controller, and appropriate control signals are generated according to the instruction.

Internal CPU Block Diagram

• Internal block diagram of a CPU shows the Arithmetic Logic Unit, has Flags, connected to the Instruction Pointer.
• The Instruction Register uses the Instruction Decoder, whose timing and control signals can be generated by the control bus.
• The CPU uses the address and data busses.
• Some internal CPU registers are Register A, Register B, Register C, and Register D.

Disadvantages of Microprocessors

• Microprocessors can only handle digital signals; analog signals require an ADC circuit for conversion to expose the microprocessor to the signal.
• Linking to a computer is challenging because external connections use SERIAL or USB ports.
• Serial ports receive data sequentially, while microprocessors receive data in parallel so serial interfaces are used the convert them bidirectionally.
• Microprocessors cannot connect to the internet natively.
• Microprocessors need an external hard disk and RAM for memory.

Microprocessors versus Microcontrollers

• Microprocessors require external components.
• Microcontrollers integrate these components.

Oscillator

• An oscillator generates a periodic signal (sine wave, square wave, etc.) without needing an external input signal.
• The oscillator connected to a CPU provides a stable clock signal that synchronizes and regulates the CPU operations.

Microprocessor Features

• Larger circuit size due to external memory and I/O connections.
• Not suitable for compact systems due to size and complexity.
• A higher cost due to additional external components.
• High power consumption due to external components.
• RAM, ROM, and I/O units are external.
• Lacks power-saving.
• Typically used in personal computers where size and power are less constrained.
• Fewer registers which may limit some operations.
• Uses an external bus for memory and I/O, like the Von Neumann model.
• Central processing unit requires additional components for functionality, more complex.

Microcontroller Features

• Has a smaller circuit size as memory and I/O are integrated.
• Suitable and ideal for compact systems.
• A lower cost, with required components on-chip.
• Low power, the integrated design reduces power usage.
• RAM, ROM, CPU, and peripherals are embedded on a single chip.
• Includes power saving modes.
• Typically used in embedded systems requiring integration and efficiency.
• More registers, wide range of functions.
• Uses an internal bus with more efficient control, like the Harvard architecture.
• Comprehensive system including CPU and peripherals.
• Simpler with fewer functions, instructions necessary.

Embedded Systems

• An embedded system is an electronic/electro-mechanical system to perform a specific function using both hardware and firmware/software.
• An Embedded System is built for a particular application.
• An embedded system uses a microprocessor/microcontroller to do one task.
• A remote control is an example of an embedded system since its processor only performs one task.