Embedded Systems & Microcontrollers

Embedded Systems and Microcontrollers Overview

• A system is an arrangement where all units work together under a set of rules
• It can be a method of working, organizing, or performing tasks as planned
• A digital watch is an example of a system that displays the time
• An embedded system is a computer system with hardware and software embedded
• It can be an independent system or part of a larger system
• It uses a microcontroller or microprocessor, typically battery-operated, for a specific task
• Examples include fire alarms, coffee dispensers, smart door locks, and flight controllers

Embedded Software Architecture

• Operating Systems (OSs) running on embedded systems are called RTOS
• RTOS have strict constraints on execution time, memory, latency, and performance
• RTOS stands for Real Time Operating System

Components of an Embedded System

• An embedded system includes hardware, embedded application software, and an RTOS
• RTOS supervises the software and offers support, enabling processor run processes via scheduling algorithms to meet latency needs
• RTOS defines how the system works and sets rules for program execution
• Smaller embedded systems may not always need an RTOS
• Bare metal refers to a computer system without a base OS, where software/firmware runs directly on the hardware

Characteristics of Embedded Systems

• Embedded systems are single-functioned, performing a specific operation repeatedly
• An example is a pager
• Have design metrics to fit on a single chip or board
• Must process data quickly and use minimal power for extended battery life
• Design Metric is a metric for implementation such as cost, size, power, latencies & performance
• Application Specific Integrated Circuit (ASIC)
• Application Specific Instruction Processor (ASIP)
• Application Specific Standard Product (ASSP)

Real-Time and Reactive Aspects

• Embedded systems react to environment changes and compute results in real time
• Car cruise controllers monitor speed and brake sensors, computing acceleration/deceleration, with delayed computation that can cause failure
• They are microprocessor or microcontroller based, with control software on top of an RTOS

Memory and Connectivity

• Embedded systems require memory, embedded via Flash/ROM
• They use DRAM or SRAM as Main Memory
• Have limited virtual memory support due to timing constraints
• Flash memory is used instead of HDD for secondary storage
• They interface with peripherals for connectivity and input/output processing
• IoT devices link to networks, use software for high-end functions and offer hardware for performance, flexibility and security

Features and Challenges

• Features include easy customization, low power consumption, and low cost
• They offer enhanced performance and high operational reliability
• Challenges include high development effort, larger time to market, and high volume requirements
• The need for low power operations is also a challenge

Hierarchical Levels of Computer Systems

• Abstraction levels in computer architecture include programming language, application programming interface, operating system, assembly language, computer architecture, and digital electronics

Architecture Levels of Abstraction

• Levels of abstraction include logic level, functional block level, architecture level and system level

Core Definitions of Computer Architecture

• Computer architecture describes computer systems' functionality, organization, and implementation
• Instruction Set Architecture (ISA) defines the machine code
• Microarchitecture (or computer organization) implements the ISA, example is x86
• Systems design includes all other hardware components besides the CPU such as cache, memory, internal bus, peripherals etc

Processor Architecture Definition

• Processor architecture designs processors as multi-cores
• Details internal organization, interface with memory and peripherals
• Microarchitecture addresses ISA implementation
• Multi-core design faces cache coherency and Internal buses interfacing with memory/peripherals issues

Software Development

• Steps include edit source files, preprocess, compile (.obj files), link libraries and object files, load executable with static data, and execute program

SW Program Development Environment

• The SW Program Development involves different stages
• The process begins with editing source code, then preprocessing to handle includes
• It continues with compiling to create object code, linking to libraries, loading the program into memory, and executing it

Program to Executable

• The processes include compiling the source code and linking library files

Standard Address Space Model

• The address space has distinct regions allocated for stack, heap, static data, and code

Memory Layout of C Program

• Memory includes Main Memory (MM) and DRAM
• Higher addresses include command line arguments and stack
• Lower addresses include initialized data and code/text (assembly opcodes)

Architectural View of a Computer System

• DRAM facilitates communication between components such as a CPU, I/O modules, and data storage, enabling data processing and storage

CPU DRAM Performance Gap

• Performance gap between CPU and DRAM shown, with CPU increasing by 60% per year
• DRAM performance increased by less than 10% per year, as shown in the performance gap graph

Principle of Locality

• Programs tend to reuse data and close instructions
• Temporal locality is when recent items are often re referenced in the near future
• Spatial locality is when close addresses often get used

Code

• Array element access have both spatial and temporal locality.
• Instruction loop has both spatial and temporal locality

Types of Memory/Storage Hierarchies

• Smaller memories are faster but expensive
• Larger memories are slower but cheaper
• Exploit locality to get the best of both worlds and reuse nearness of accesses
• Results in most accesses using the smaller and faster memories combined with large with cheaper memories

Properties of Memory Levels

• If data exists at a lower level (closer to the processor), it must also exist at all higher levels
• Multiple copies of the same data must be identical
• Temporal locality is with data will be used in the near future
• Spatial locality is with adjacent data are likely to be used often, and includes sequential instructions

Important quiz

• Quiz: Memory Level Hierarchy & Access Time
• Cost per Byte ↑ as Access Time ↓
• Memory size ↑ as Access Time ↓
• Transfer Bandwidth ↑ as Access Time ↓
• Unit of transfer ↓ as Access Time ↓
• Frequency of Access ↑ as Access Time ↓

Different Memory Types

• Memories are classified as Semiconductor and Non-semiconductor
• Semiconductor included RAM and ROM
• RAM is divided in SRAM and DRAM
• ROM is divided into EPROM, UVEPROM and EEPROM
• Non-semiconductor include secondary and auxiliary memory
• Auxiliary Memory divided into Floppy Drive, Hard Disk Drive and Compact Disk, Digital Versatile Disk

Volatile and Non-Volatile Memory

• Volatile memory loses contents when power is off
• Non volatile memories maintain contents even with power off
• Advantage of RAM is direct access by CPU, faster than non-volatile memories.
• Non-volatile examples are flash, hard disk and SSD

Semiconductor vs Non Semiconductor

• Semiconductor uses special technologies and is random access, mostly volatile, close to the CPU and in GBytes
• Non Semiconductor are magnetic and optical, sequential access, non volatile, further from CUP and sized in TBytes

Read Only Memory ROM

• It defines what a ROM is, and then the different types of ROM´s
• Describes the classifications as semiconductor and non semiconductor

Programmable Read Only Memory (PROM)

• A PROM non-volatile, written to once, done electrically
• Writing may be performed by the supplier or the user after fabrication
• Programming requires special equipment
• Often called One Time Programmable (OTP) with NVM
• More expensive then ROM, which is better for high production runs

Erasable Programmable Read Only Memory(EPROM)

• Used UV light to erase, and therefore you must erase the whole chip
• Must erase the whole chip for 20min to erase all contents
• This memory is covered with film to prevent accidental lighting

Electrically Erasable Programmable Read Only Memory (EEPROM)

• Is more attractive form of ROM and electrical written
• Updating only a byte or a set of bytes is possible
• The process takes long time of several 100 µsecs
• Has both advantage of being non- volatile and in circuit updates
• EPROM is more expensive and less dense
• EEPROM fewer bits per chip than EPROM

Random Access Memory

• Data can be read and written in uniform time
• Direct access includes Hard Disks DVDs and the time need to take varies depending on location

Types of Random Access Memory

• The computer memories are primary built are Dynamic RAM (DRAM) and Static RAM (SRAM)
• There each volatile, which means and data is lost when shut off

Usage for SRAM and DRAM

• Processors find data in the small fast cache usually on the same ship
• If the data is not in cache, then the looks in main memory.
• If this not there, the fetches the data from the hard disk

Quiz- Hibernate and Sleep

• What happens when latptos on hibernates adn sleep mode
• Sleep- display and other peripherals is switchefd off, but the mani memory is pwoered. I retains the contenst so quickly restart
• Harid disk- contents of hte mamni meory is saved inot hraid ski and RAM is woff. It takes more time o copy content bac from the ram starts running them