Introduction to Embedded Systems

Course Objectives

• Understand the operation of microprocessors and microcontrollers
• Learn machine language programming and microprocessor interfacing techniques
• Design and interface microcontroller-based embedded systems in both hardware and software
• Master basic programming of ARM Cortex chips using assembly language
• Learn the fundamentals of embedded system design
• Ultimate goal: Apply this knowledge to more advanced structures.

Embedded Systems

• Special-purpose systems perform dedicated functions
• Computer systems embedded inside electronic devices, but not general-purpose computers
• Characteristics include being dedicated to specific functions, interacting with the environment, and having real-time requirements
• Application examples: microwave oven front panels, Canon EOS 3 camera, digital TV, a smartphone, vehicle control, nuclear power plant control
• Implemented using microcontrollers or digital circuits
• Microcontrollers (or microprocessor-based systems): Slower but software can be updated
• Digital circuits or Field Programmable Gate Arrays (FPGAs): Faster but function changes are difficult

Microcontrollers

• A full computer system on a chip, although resources are limited
• Designed for standalone applications
• Basic components: CPU, temporary memory (registers, cache), main and secondary memory, input/output modules

Microprocessors

• A component performing instructions and tasks for computer processing
• When integrated with memory, I/O, and other functionalities, becomes a microcontroller
• Can be single-core or multi-core
• Multi-core processors have two or more independent cores or processing units
• Arithmetic Logic Unit (ALU): Circuitry capable of performing operations like ADD, SHIFT, AND, OR on on-chip registers
• Control Unit: Directs processor operations and instructs memory, ALU, and I/O devices
• Registers: Small storage within a microprocessor
• System Bus: Connects major computer components, carrying information, addresses, and control signals

I/O Ports

• External devices connected to the microcontroller give functionality to the system
• An input port is hardware on a microcontroller that allows information about the external world to be entered into the computer
• An output port is hardware on the microcontroller to send information out
• Interface Includes I/O ports, external electronics, physical devices, and software
• Classifications of I/O interfaces:
• Parallel: Binary data available at once
• Serial: Binary data sent one bit at a time
• Analog: Data encoded as voltage, current, or power
• Time: Data encoded as period, frequency, pulse width, or phase shift
• I/O ports available on the Tiva C series board: UART, SSI, I2C, Timer, PWM, ADC, Analog comparator, QEI, USB, Ethernet, CAN

Memory

• Random Access Memory (RAM): Equal access time for any location.
• Read/write capable
• Read-Only Memory (ROM): Can only be read.
• Cannot be directly written to by the processor
• Dynamic Random Access Memory (DRAM): Requires periodic refresh to maintain contents
• Static Random Access Memory (SRAM): No periodic refresh
• Predictable and faster than DRAM
• Synchronous DRAM (SDRAM): Synchronous interface requires a clock signal
• Divided into banks for concurrent operations, improving concurrency and data transfer
• Mask-Programmed ROM (MROM): Programmed during manufacturing
• Programmable ROM (PROM): Programmed by the end user
• Erasable Programmable ROM (EPROM): Electrically programmable and erasable using ultraviolet light
• Electrically Erasable Programmable ROM (EEPROM): Electrically programmable and erasable at the location level
• Flash Memory: Electrically programmable and erasable only in bulk blocks
• The Tiva C Series TM4C123G microcontroller has 256KB of flash memory, 32KB of RAM, and 2KB of EEPROM

Developing Embedded Applications

• Embedded system development requires synchronized hardware and software development
• Factors in Microcontroller Selection
• Peripherals and interface features, such as the number of I/O ports and types of serial communication modules
• Memory size requirements
• Processing speed requirements
• Low power requirements
• Performance and maximum frequency
• Chip package
• Operation conditions: voltage, temperature, electromagnetic interference
• Cost and availability
• Software development tool support and kits
• Future upgradability
• Firmware packages and firmware security
• Availability of application notes, design examples, and support

Software Development

• Program Instructions
• Machine Instruction: Binary code executed by the processor
• Assembly Language: Mnemonic representation of machine code instructions
• High-Level Language: English-like syntax, translated by a compiler
• Assembly programs are more optimized
• Microcontrollers have different word sizes, memory types, and architectures.

Address Space

• Memory is a sequence of addressable locations
• A memory location has an address and its contents.
• CPU and memory communicate through address and data buses.
• The address space depends on the processor’s address decoding mechanism
• Different address space usage approaches
• Isolated I/O: Separate spaces for memory and I/O. (Intel)
• Memory-mapped I/O: Single address space for both. (ARM, Motorola)
• The Cortex-M4 processor has 32 bits for addressing, supporting 4GB of memory space

Data Organization

• Memory stores data in fixed-size locations (typically 8-bit bytes), each with a unique address
• Memory content is accessible by size: byte, half word, word, double word
• A 32-bit piece of data has four bytes, depends on endianness
• Little Endian: LSB stored in the lowest address (ARM default)
• Big Endian: LSB stored in the highest address

Memory Architecture

• Two classes
• Von Neumann: Data and program share memory
  • Requires a single memory interface bus, but bottlenecks data transfer
• Harvard: Separate buses for code and data to improve performance
  • Requires sophisticated hardware to support multiple interface buses
  • The Cortex M4 is based on the Harvard architecture

Registers

• They are closely located in the processor
• Fast access, but limited quantity
• General-purpose registers store data (timer values, constants) and addresses (ASCII tables, stack)
• Some are reserved for specific purposes like program counters and program status registers.

Instruction Set Architecture (ISA)

• ISA provides an interface for communication
• Elements in ISA
• Instruction Set:
• Group of instructions to the computer
• Instructions direct computer in terms of data manipulation -Opcode or operational code: Instruction that's applied
• Operand is memory register or data which instruction is applied on
• Addressing Modes: Specifies how data is accessed -Direct mode accesses data in a indirect way -Indirect mode access is straight data

CISC and RISC

• Complex Instruction Set Architecture (CISC) approach minimizes instructions per program, sacrificing cycles per instruction -Complex hardware design, slower execution. Reduced Instruction Set Architecture (RISC) decreases the cycles per instruction
  • Needs more instructions and memory
• ARM provides the 16-bit Thumb and 16/32-bit Thumb2 instruction sets

Instruction Execution

• Multiple stages in executing an instruction
• Fetching
• Decoding
• Executing
• Cortex M4 uses a 3 stage pipeline

ARM Architecture

• 1980s ARM Acorn computers
• ARM based an RISC developed by Advanced RISC machines
• requires lesser transistors
• smaller size
• low power consumption
• has modular design
• can be grouped by different architectutres, families and cores

Arm Processors

• Various bit widhts, for instance ARMv4T with 32, ARMv5 with 32 etc
• Cortex AX implements Virtual Memory Systems arch based on MMU
• ARM Processor licenses includes ARMv8A, CortexA15

Registers

• Has 32 bit registers
• General purpose registers r0-r12
• Stack Pointer SP
• Link Register
• Program Counter
• Some register can be reached accoringly

Cortex M3/M4 CPU

• Has Flash Memory
• Has IO Code bus with Instuction Fetch
• Has data and debug data

Data Processing

• Data can be handeled efficiently with 8/16 bit
• Support operating systems
• Support memory protection
• Has instructions for system control

Thumb instructions

• 16 bit instruction set, some can access high register
• alligned and half-worded
• Various types, for instance data movement, arithmetic
• APSR 32 bit register holds the flag bits

ALU Support

ALU Supports a barrel shifter that has powerful instruction when shifting