Transcript Slide 1

Embedded Systems
Introduction 09/10
Embedded Systems 16-5147
Alan Holloway
– contact: [email protected]
– Room 9323 Furnival
• 12 × 1 Hour Lectures
• 12 × 2 Hour Labs (staffed for 1 Hours)
• 100% Coursework
– formative series of lab tutorials (10%)
– 5 × Homework questions ( 2% each )
– major assignment (80%)
Resources
• All course information can be found at
www.aholloway.co.uk follow link for this unit
– Lecture notes
– Sample programs
– Reading list
– Software (available free)
What is an embedded system?
• An embedded system is a special-purpose
computer system designed to perform one or
a few dedicated functions
•Washing machine runs programs
•Open water valve
•Heat water
•Start spin
•etc etc….
•Do we need a PC running windows Vista to
do this ?
Will I ever need to use one?
• Over 4 billion 8-bit microcontrollers were sold
in 2006 alone
• the world's population is estimated to be
about 6.756 billion
• Average car contains >50 microcontrollers
• Electrical, electronic, control, robotics,
computer engineer - Yes you will
Embedded Systems
• Microprocessor Systems
• Microcontrollers
• ARM7 core Processor Family
– specifically NXP LPC2368 microcontroller
– Many others are available 8051, PIC, AVR etc
• C Programming will be used throughout
– ARM Realview MDK - 'C' compiler & other tools
– u-Vision Integrated Development Environment
1-6
Microprocessor system
•
•
•
•
CPU
Memory – ROM and RAM
Input – various
Output - various
1-7
Bus system
• Devices connect to microprocessor via bus
system (often called the memory bus)
• A devices connected to bus must be tri-state
devices
– only one device is activated at a time
• Consists of 3 bus types
– Address bus
– Data bus
– Control bus
1-8
address
decoder
chip enable signals
address bus
data bus
a
d
CE
CE
CE
reset
uP
ROM
RAM
Additional
devices
I/O
clock
OE
WR
OE
WR
OE
read
write
Microprocessor System Structure
1-9
Bus operations
• Read
• Write
• Each read/write operation is made up of a
number of clock cycles or T states
• Each machine instruction is made up of one or
more read and/or write operations
• This is why we shouldn't compare
microprocessors simply based on clock speed
1-10
Address Bus
2a - 1
• Unidirectional and generated by microprocessor
• Number of address lines determines number of address
locations
• Addressable locations = 2^a where a is the number of
address lines
Total
memory
space
FFFFH
1
0
memory
addresses
d bits
Memory Map :
A memory map shows the
position of devices within the
whole of the addressable area
I/O
E00FH
E000H
7FFFH
RAM
6000H
3FFFH
ROM
1-11
0000H
Memory
Address
Data Bus
• Bi-directional
• Usually matches the word length of the
microprocessor
• Usually a multiple of 8
• We talk of 8-bit, 16-bit , 32-bit and 64-bit
processors which refers to the normal word
length of the microprocessor
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Control bus
• Consists of potentially many signals. Typically:– Read
– Write
– Could be single signal - Read/notWrite line
– Interrupt control
– Bus control signals for DMA (Direct Memory
Access)
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Microprocessr
• CPU – Central Processing Unit
– ALU – Arithmetic Control Unit
– Registers
– Control Unit
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Microprocessor Registers
• General purpose registers
• Accumulator – used in conjunction with ALU –
often found on 8-bit microprocessors
• Status or Flag Register – indicate result of last
instruction executed
• Program counter(PC) or Instruction Pointer
• Stack Pointer (SP)
• Special registers – Instruction and memory
address register
1-15
The Fetch – Execute cycle
• Fetch
– memory read cycle
– place in instruction register and decode
• Execute
– may involve additional read and/or write cycles
• Often the whole Fetch-Execute cycle is carried
out through a pipeline operation involving several
stages.
– 5 stages are often used (IF, ID, RR, EX, WB)
– The Pentium 4 has 20 stages
– The ARM 7 has 3 stages
1-16
Pipeline - Natural assembly line
• Example
– Alan (A) Barry (B) & Chris (C) each have a load of clothes
A
• Washer takes 30 mins
• Dryer takes 30 mins
• Ironing takes 30 mins
B
C
Sequential - non pipelined
7pm
30
11.30pm
30
30
30
30
30
30
A
B
C
Total for 3 Loads is 4.5 Hours
30
30
Pipelined
7pm
30
11.30pm
30
30
30
30
30
30
A
B
C
• Total for 3 loads pipelines 2.5 hours
30
30
Pipelines
• Does not speed up 1 task - increases overall
throughput
• Multiple tasks operate simultaneously using
separate resources
• Limited by speed of slowest resource
ARM7 Pipeline
• The pipeline has hardware-independent stages that execute
one instruction while decoding a second and fetching a third.
The pipeline speeds up the throughput ofCPU instructions so
effectively that most ARM instructions can be executed in a
single cycle.
• The pipeline works most efficiently on linear code.
CPU operation
• On reset – PC is loaded with a value, typically 0
• Fetch – execute cycle
– Fetch instruction
• memory read cycle using PC (program counter)
• place in instruction register and decode
• increment PC ready for next fetch
– Execute instruction
• often involves additional read and/or write cycles to read
operands and possibly write back results
• could modify PC – causes flow of program execution to
change
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CPU Architecture
• Two basic types
– Von Neumann
• One memory space for instructions and data
• Therefore one single memory bus structure
– Harvard
• Separate instruction and data spaces
• Therefore separate memory buses – parallel operation
and therefore faster operation
• Can have different address and data bus widths
optimised for each bus
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Basic microprocessor system
• Von Neumann Architecture
Microprocessor
Power on
& manual
reset
Address
Reset
A0-Ax
Data
Clock
Oscillator
Memory
(Instructions &
Data) and
Input/Output
D0-dy
Read
Write
1-24
Harvard Architecture
Microprocessor
Address
Address
Program
Memory
A0-Ay
Instruction
I0-Iw
Read
A0-Ax
Data
Memory &
I/O
Data
d0-dn
Read
Write
1-25
Microcontroller
• A microcontroller is the integration of
– microprocessor
– memory
• ROM types – commonly flash PROM
• RAM – Static ram
– peripherals
•
•
•
•
•
parallel input and output(digital I/O)
Timers and Counters
Serial input and output (UART, USART, SPI etc.)
Analogue to digital converters
PWM, CAPCOM registers, DACs etc.etc.
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What is an Embedded Computer System
• Special purpose computer – usually with one
specific task or application.
• Usually embedded in a device which often
has other electronic and mechanical parts
• Usually optimised for the specific task
• Has the usual basic computer components –
CPU, memory, inputs & outputs
Examples
• consumer appliances
– tv's, mp3 players, dvd's, washing machines etc.
• automotive applications
– engine management, anti-lock braking
• computer peripherals
– hard disk controllers, routers, switches
• medical equipment
– scanners, blood analysers
• telecoms
– mobile phones
• aerospace
– satellite control systems, avionics
Some Characteristics
• Very simple to very complex applications
• Often single application
– but concurrent operation
• Could be real-time (hard and soft)
• Program is normally stored in ROM – called
firmware – flash ROM commonly
• Could be critical applications
• Interfacing with other devices via peripherals
• Require a range of development tools – hardware
and software
• May use operating system (RTOS)
Constraints
•
•
•
•
Physical size
Weight
Power usage
Performance – throughput and/or response
time
• Cost
Resulting in • limited space
• limited processing power
– 8-bit processor
• limited memory RAM & ROM
– only Ks of memory not Ms
• schemes to limit power consumption
– low power modes
– sleep
– standby
• determinism – needed for RT guarantee
Microprocessor vs Microcontroller vs Soc vs
FPGA
• uP
– General purpose
– external memory and peripherals
– connected by a memory bus
• uC
– uP integrated with memory and peripheral
interfaces
– families of uC all with same uP but varying
amounts and types of memory and interfaces.
Microcontroller (µC) vs. Microprocessor (µP)
• µC intended as a single chip solution, µP requires
external support chips (memory, peripheral
interfaces etc.)
• µC has on-chip non-volatile memory for program
storage, µP does not.
• µC has more interface functions on-chip (serial
interfaces,Analog-to-Digital conversion, timers, etc.)
than µP
• General purpose µPs are typically higher
performance (clock speed, data width, instruction
set, cache) than µCs
• However the division between some µPs and some
µCs becoming increasingly blurred.
1-33
FPGA/PLD
• A field-programmable gate array is a semiconductor device
containing programmable logic components called "logic
blocks", and programmable interconnects. Logic blocks can be
programmed to perform the function of basic logic gates such
as AND, and XOR, or more complex combinational functions
such as decoders or simple mathematical functions. In most
FPGAs, the logic blocks also include memory elements, which
may be simple flip-flops or more complete blocks of memory
Microprocessor vs Microcontroller vs
SoC vs FPGA
• SoC – System on a chip
• FPGA – Field
Programmable Gate Array
Core
Rest of FPGA
contains standard
logic
Microcontroller-based System-on-a-Chip