introduction to embedded systems part 1

EMBEDDED SYSTEMS
Eng : Hatem Abd El-Salam
INTRODUCTION 1

COMPUTER
• The computer is device that I write a code on it and it is doing an operation
Component:
 Processor
 Memory
 IO
Processor
IO Memory

EMBEDDED SYSTEMS
• Embedded systems is computing system have
 Processor
 Memory
 IO
• But minimal specification because it has one job
• It is two ways to impalement Embedded systems
 System On Chip (SOC)
 System Board (SB)

SOC SB
Performance The same The same
Cost Cheaper Costly
Power consumption lower higher
size smaller bigger
SOC VS SB
• Microcontroller is a SOC.

MICROPROCESSOR VS MICROCONTROLLER

MICRO-CONTROLLER
• Basically a microcontroller can be described as a computer on a chip. a
single chip containing a CPU, non-volatile memory (RAM), volatile
memory(ROM), a timer and an I/O control unit.
• A microcontroller apart from the above mentioned components usually also
include serial communication capabilities, interrupt controls and analog I/O
capabilities.
• Used for a few dedicated functions determined by the system designer.

MICRO-CONTROLLER
• Microcontrollers don’t work alone in the circuit it must interfaces with other on
chip devices like Sensors, Switches, Leds, LCD, Keypad and DC Motor
• Microcontroller can accept inputs from some components and provide outputs
to other components within any given system.
• Differences in requirements, make the manufacturers produce different
microcontrollers with different memory sizes, number of I/O lines and number
of integrated peripheral devices. Other wise they are all similar to use.

MICRO-PROCESSOR
• Just a CPU has to add externally memory, clock, input/output interfaces, timer
and all other needed peripheral. This is the reason a microprocessor has so
many pins.
• The difference between a microcontroller and a microprocessor is that the
microprocessor is a general purpose computer while a microcontroller is a
computer dedicated to one or just a few tasks.
It contains :
 Control Unit (CU)
 the Arithmetic Logic Unit (ALU)
 Instruction Decoder and some Special Registers

MICRO-PROCESSOR
• Microprocessor function: is to fetch the instructions from the memory then
decode and execute them.
• Example:
• CPU=ALU + Registers + Control unit
• Microprocessor alone is useless

MICRO-PROCESSOR
Control Unit:
• The control unit is the circuitry that controls the flow of data through the
processor, and coordinates the activities of the other units within it.
• In other word it is in charge of the entire Instruction (Machine) cycle

MICRO-PROCESSOR
Arithmetic Logic Unit :
• An ALU is an integrated circuit within CPU or GPU that performs arithmetic and logic
operations.
• Arithmetic instructions include:
 Addition
 Subtraction
 shifting operations
• Logic instructions include:
 AND
 OR
 XOR
 NOT operations

CPU Registers
• Program Counter
(PC)
• Instruction
Register (IR)
• Instruction
Decoder (ID)
• Stack Pointer
(SP)
• Status Register
(SREG)
• Index Registers
(X,Y)
• Accu. Registers
(A,B)
• General Purpose
Registers (GPR)
(R0, R1,
……R31)
Internal Buses
• Data Bus
• Address Bus
• Control Lines
CPU Architectures
• Harvard
• Von Neumann
Instruction Sets
• CISC
• RISC

PROGRAM COUNTER (PC)
• Most important CPU register
• Holds the address of the next instruction in program memory space
• The size (width) of the program counter is directly related to the size of the
μC’s program memory

INSTRUCTION REGISTER (IR)
• Contains the next instruction (Op-Code) to be decoded by the Instruction
Decoder.

INSTRUCTION DECODER (ID)
• Takes Op-Code stored in the instruction register and decodes it then tells the
CPU what to do for it and enable the components for this operation

STACK POINTER (SP)
• The stack pointer is basically a register that holds either:
 "the memory address of the last location on that stack where data are stored“ or
 "the memory address of the next available location on the stack to store data"
• The definition depends on the design of the μC

STATUS REGISTER (SREG)
• Contains flags represent the status of the last operation to control the following instructions
• Flags as:
 Overflow flag
o Indicates that the result is too large to fit in the register width.
 Negative flag
o Indicates that the result is negative
 Zero flag
o Indicates that the result was zero.
 Carry flag
o Indicates a carry in the last arithmetic or logical operation
 Half-carry flag
o Indicates that a bit carry was produced between the 4-bit halves of a byte operand as a result of the last arithmetic
operation
 Global Interrupt mask

INDEX REGISTERS
• Index Register : Used in indirect addressing modes, as the accessed
• address = index register + offset mentioned in code

ACCUMULATOR REGISTERS
• An Accumulator is a register in which intermediate arithmetic and logic results
are stored
• Access to main memory is slower than access to a register like the accumulator
because the technology used for the large main memory is slower (but
cheaper) than that used for a register.

GENERAL PURPOSE REGISTERS (GPR)
• General purpose registers are available to store any transient data required
by the program.
• In general the more registers a CPU has available, the faster it can work.

DATA BUS
• These are the lines that actually carry the data being transferred
• Wider data buses generally mean higher performance
• The bandwidth of the data bus is how much information can flow through it,
and is a function of the bus width (in bits) and its speed (in MHz)

ADDRESS BUS
• The address bus is the set of lines that carry information about where in
memory the data is to be transferred to or from
• The width of the address bus controls the address ability of the processor,
which is how much system memory the processor can read or write to
• The width of the address and data buses aren't linked

CONTROL LINES
• The control bus carries commands from the CPU and returns status signals
from the devices.
• For example:
 Memory chip READ/WRITE (R/W) lines
 IO device Chip Enable (CE) lines

HARVARD
• Separate memory areas for program instruction and data
• Two or more internal buses which allow simultaneous access to both instructions
and data
• If the fetched instruction requires an operation on data memory, the CPU can
fetch the next program instruction while it uses the data bus for its data
operation
• Speed up execution time with cost of more hardware complexity

VON NEUMANN
• Has a single common memory space for Data and Program instructions
• Single data bus which fetches both instructions and data
• Each time the CPU fetches a program instruction it may have to perform one
or more read/write operations to data memory space. It must wait until these
subsequent operations are complete before it can fetch and decode the next
program instruction. (Von-Neumann bottleneck)
• The advantage of this architecture lies in its simplicity and economy

CISC
• Complex Instruction Set Computer (CISC)
 CISC is an old concepts that dates back when memory access was slow
 CISC aimed to integrate several functionalities in one instruction, in order to limit the
program size, and thus limit memory access in order to gain some speed
 Number of instructions are reduced by having multiple operations within a single
instruction
• Examples: x86, Motorola 68k

RISC
• Reduced Instruction Set Computing (RISC)
 As memory technology developed more and more, memory access became faster
 RISC aims to optimize execution of instructions by limiting the capabilities of a single
instruction and having consistent instructions’ execution time (Instruction Pipelining)
 Large and uniform register file
• Small number of instructions that actually reference memory (e.g. STORE, LOAD)
• All other instructions work on the registers only
 Hardware that helps parallel operations (Harvard architecture)
• Examples: ARM, Atmel AVR, PowerPC

CISC VS RISC
Consider this example:
• This CISC assembly code
clear 0x1000 ; clear memory location 0x1000
• Becomes the following RISC assembly code
xor r1,r1 ; clear register 1
store r1,0x1000 ; clear memory location 0x1000

CISC VS RISC
The Performance Equation:
• The following equation is commonly used for expressing a computer's
performance ability:
 The CISC approach attempts to minimize the number of instructions per program,
sacrificing the number of cycles per instruction.
 RISC does the opposite, reducing the cycles per instruction at the cost of the number of
instructions per program.

introduction to embedded systems part 1

introduction to embedded systems part 1

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introduction to embedded systems part 1