Embedded Systems Power and Clocking Units

Power Source

Embedded systems usually have a dedicated power supply with separate rails for I/O, clock, processor, memory, and analog units.
A power supply source or charge pump is crucial for system operation, using switching devices to connect supply voltage to a load.
Common voltage ranges for embedded system units include 5.0V±0.25V, 3.3V±0.3V, 2.0V±0.2V, and 1.5V±0.2V.

Clock Oscillator Circuit and Clocking Units

Essential to utilize an appropriate clock oscillator circuit.
Real-Time Clock (RTC) and timers control the timing for hardware and software processes.

Reset Circuit

The program counter increments or changes upon execution of a program.
Reset options can include a system program, boot-up program, or initialization program.
The Watch Dog Timer (WDT) ensures system reliability by detecting malfunctions and preventing system hangs.

Memory

Memory in embedded systems can be classified as internal or external.
Internal memory is limited; external memory may be necessary for larger applications.
ROM, EPROM, or Flash is used for storing application programs and boot codes.
Internal, external, and buffer RAM store variables and I/O buffers for active programs.

Interrupts Handler

Manages various interrupts including external port interrupts, I/O interrupts, timer interrupts, RTC interrupts, and software exceptions.

I/O Communication Unit

Network communication can occur via Ethernet or serial drivers to connect with hosts.
Supports various serial buses:
- UART (512 kbaud/s)
- 1-wire CAN (33 kbps)
- Industrial I2C (100 kbps)
- SPI (100 kbps)
- USB 2.0 (up to 480 Mbit/s)
Parallel buses include PCI (266 MB/s) and PCI-X (4,266 MB/s).

Software Tools for Designing Embedded Systems

Code editing in languages like C or C++ is performed using editors.
Compilers convert source code into object code.
Assemblers transform assembly language into machine language.
Debuggers analyze code for errors and bugs.
Linkers merge object and library files to create an executable program.
Libraries consist of reusable C/C++ code for multiple programs.
Simulators provide real-time code behavior visualization.
Integrated Development Environments (IDEs) include essential tools for embedded software creation.

Embedded System Design Process

Design begins with abstraction of problem components.
Hardware and software architecture must be understood before design proceeds.
Consider extra functionalities needed in the system.
Design modules are based on previously developed related systems.
Ensure modular design for faster development and protection of module functionality.
Mapping involves aligning software requirements with hardware capabilities.
User interfaces require design considering end-user needs, such as GUI or VUI.
Iterative refinements improve each module's design before implementation.

Memory Types in Embedded Systems

Memory types include:
- Primary Memory: Directly addressed by the processor, includes RAM for temporary data.
  - Static RAM is made of flip-flops and stores data as voltage.
Secondary Memory is generally not found in embedded systems, limiting data storage options.

Hardware Architecture for Embedded Systems

Built around a processor which performs computations based on inputs from external devices.
CPUs in embedded systems are less powerful compared to desktop CPUs.
Limited internal memory may mandate the use of external memory devices.
Hardware includes user-interaction components like displays and keypads.

Types of Processors in Embedded Systems

Microcontrollers: Integrated processor with memory and peripherals.
Microprocessors: General-purpose CPU.
Digital Signal Processors: Specialized processors for processing digital signals.

Characteristics of Embedded Systems

Operate as independent systems or as part of larger systems with specific functions.
Designed for dedicated tasks within time constraints, lacking multitasking capabilities.
Must operate reliably under deadlines; failure can lead to critical consequences (e.g., safety in real-time applications).
Capable of functioning in extreme environmental conditions.
Utilize various operating systems and processors distinct from typical desktop computer options.

Types of Memory Characteristics

SRAM (Static RAM): Volatile memory, writeable by byte, unlimited erase cycles, fast speed.
DRAM (Dynamic RAM): Volatile memory, writeable by byte, unlimited erase cycles, moderate speed.
Masked ROM: Non-volatile, not writeable, fast speed.
PROM (Programmable ROM): Non-volatile, writable once with a programmer, fast speed.
EPROM (Erasable Programmable ROM): Non-volatile, writable fully using a programmer, limited erase cycles, fast speed.
EEPROM (Electrically Erasable Programmable ROM): Non-volatile, writable by byte, limited erase cycles, fast reads but slow writing/erasing.
Flash Memory: Non-volatile, writable by sector, limited erase cycles, fast read speed but slow write/erase.
NVRAM (Non-Volatile RAM): Non-volatile, writeable by byte, unlimited erase cycles, fast speed.

Direct Memory Access (DMA)

DMA is used for transferring large amounts of data from peripheral devices directly to the system, bypassing interrupt-based methods.
Context switching for interrupts is time-consuming, making DMA more efficient.
It utilizes six transistors: four for flip-flops and two for control access.

Read-Only Memory (ROM)

ROM stores application programs, instruction codes, and system booting codes, retaining data even when powered off.
Masked ROM: One-time programmable, suitable for low-cost, high-volume production.
PROM: Programmable by the end user, featuring Nichrome or polysilicon wiring.
EPROM: Erasable via UV light, allowing reprogramming.
EEPROM: Electrically reprogrammable, altering data using electrical signals.
Flash Memory: Combines features of EEPROM and ROM for high-capacity storage.

Secondary Memory

Not directly accessed by the processor; used for long-term data storage.
Offers substantial storage capacity compared to primary memory, with examples including hard disks, floppy disks, and CDs.
Essential for high-end OS and application software, meeting the increasing demands for virtual memory in embedded systems.

System Design Considerations

Understanding hardware and software architecture is crucial before the design process.
Identify extra functions and requirements needed for system development.
Consider existing designs of related system families for insights and efficiencies.
Adopt a modular design by breaking down software into manageable modules that maintain continuity and apply appropriate protection strategies for each.
Ensure mapping of software requirements to suitable hardware equipment.
User interface design should align with user needs, utilizing interfaces like GUI or VUI.
Iteratively refine components and modules for optimal suitability for implementation.

Types of Memory in Embedded Systems

Memory can be classified as primary (directly addressed by the processor) or secondary (not directly addressed).
Primary Memory: Includes RAM, which is volatile and used for temporary data storage and stack management.
Static RAM: Utilizes voltage levels for data storage and employs flip-flops for memory architecture.

Classification of Embedded Systems

Embedded systems are categorized into three types based on microcontroller performance:
- Small Scale Embedded Systems
- Medium Scale Embedded Systems
- Sophisticated Embedded Systems

Small Scale Embedded Systems

Characterized by simple application needs.
Performance is not time-critical.
Typically built around low-performance, low-cost 8 or 16-bit microprocessors/microcontrollers.
Example application includes electronic toys.

Medium Scale Embedded Systems

Slightly complex in terms of hardware and firmware.
Built around medium performance, low-cost 16 or 32-bit microprocessors/microcontrollers.
Often include an operating system.
Example applications involve industrial machines.

Sophisticated Embedded Systems

Highly complex hardware and firmware requirements.
Built around advanced 32 or 64-bit RISC microprocessors/microcontrollers, programmable logic devices (PLDs), or multicore processors.
Time-critical response is essential.
Example applications are mission-critical systems.

Core Components of Embedded Systems

Processor: The heart of an embedded system, requiring a solid understanding of both microprocessors and microcontrollers.
Architecture: A well-structured hardware and software architecture is crucial before design.
Extra Function Properties: Additional functionalities necessary for the system must be clearly defined.
System-Related Family Designs: Considerations of previously developed related systems aid in design efficiency.
Modular Design: Fast system design achieved through decomposing software into manageable modules, ensuring continuity and protective strategies.

User Interface Design

Tailored specifically to user requirements.
Examples include touch screen and voice user interfaces for applications like automatic vending machines.

Memory Types in Embedded Systems

Memory can be classified as either internal or external, with internal memory typically limited.
Primary Memory:
- Directly addressed by the processor.
- RAM (Random Access Memory): Used for temporary data storage.
  - Static RAM: Stores data in voltage using flip-flops.

Definition of Embedded System

An embedded system integrates dedicated-purpose software within hardware for specific applications or functions, often part of larger systems.
System-on-a-chip (SoC): A microchip containing all necessary electronic circuits and parts on a single integrated circuit, used in devices like smartphones.

Characteristics of Embedded Systems

Functionality is dedicated to specific tasks.
Complex algorithms tailored for dedicated purposes.
User interfaces (GUIs) designed specifically for applications.
Real-time operation capabilities to manage events and execution timing.
Multi-rate operation allows for varying speeds in processing different events.

Constraints in Embedded System Design

Limitations include:
- System memory availability.
- Processor speed constraints.
- Power dissipation during continuous operations.
- Indicators of performance, power, size, and associated costs (design and manufacturing).

Memory Types Characteristics

Secondary storage devices offer much larger memory than memory chips but require moving parts for writing and reading data.
SRAM: Volatile, writable by byte, unlimited erase cycles, and fast.
DRAM: Volatile, writable by byte, unlimited erase cycles, moderate speed.
Masked ROM: Non-volatile, non-writable, fast with no erase cycles.
PROM: Non-volatile, writable once with a device programmer, fast and no erase cycles.
EPROM: Non-volatile, writable with a device programmer, limited erase cycles, requires erasure via UV exposure, and fast.
EEPROM: Non-volatile, writable by byte, limited erase cycles, fast to read and slow to erase/write.
Flash: Non-volatile, sector-writable, limited erase cycles, fast to read and slow to erase/write.
NVRAM: Non-volatile, writable by byte, unlimited erase cycles, and fast.

Direct Memory Access (DMA)

DMA increases efficiency by transferring large data sets from peripheral devices directly to memory without interrupting the CPU.
Reduces context switching delays associated with traditional interrupt-based mechanisms.
Supports data transfer in multiple modes:
- Multi-byte data sets
- Bursts of data
- Blocks (bulk) of data

Embedded Systems Hardware Architecture

An embedded system centers around a CPU, performing computations based on input from external devices.
CPUs in embedded systems are typically less powerful than those in desktops, with limited internal memory.
If internal memory is insufficient, external memory devices are utilized.
Interfaces like displays and keypads facilitate user interaction.
Built using 6 transistors: 4 for flip-flops, 2 for control access.

Types of Memory in Embedded Systems

Dynamic RAM: Stores data as charges, consists of 1 MOSFET and 1 capacitor.
ROM (Read-Only Memory): Non-volatile, stores application programs and instruction codes, retains contents after power off.
Masked ROM: One-time programmable, advantages in low cost and high-volume production.
PROM: User-programmable with Nichrome or polysilicon wires.
EPROM: Erasable and programmable, data stored in bits, erased using UV light.
EEPROM: Allows electrical alterations and is programmable.
Flash: Combines EEPROM programmability with the high capacity of traditional ROM.

Secondary Memory

Not directly addressed by processors; programs and data stored long-term in devices such as hard disks, floppy disks, and CD-ROMs.
Offers significantly larger storage than primary memory.
High-end operating systems and applications often require extensive programs and virtual memory, driving the demand for secondary storage in embedded devices like automation systems and mobile devices.