EMBEDDED SYSTEMS

What is Embedded Systems?

• Which is designed/developed to perform one or more(limited) dedicated task

“An Embedded System is a microprocessor/microcontroller based system that is embedded as a subsystem, in a larger system (which may or may not be a computer system)”

• Application Oriented

• Must have Microcontroller/Microprocessor

• Connected Peripherals

• Must have memory ( most of them )

Quiz: Name one without memory?

• Real Time Constraints of System

Application areas

• Automotive electronics

• Aircraft electronics

• Trains

• Telecommunication 3

Application areas

4

AuthenticationAuthentication

Military applicationsMilitary applications

Medical systemsMedical systems

Application areas

Consumer electronicsConsumer electronics

5Smart buildingsSmart buildings

Fabrication equipmentFabrication equipment

• Difference between a Microprocessor and Microcontroller?– Note : RAM, ROM, I/O, Timer, Serial Com port

Quiz :Examples of Both

• How to decide which one to select ?1. Cost

2. Speed

3. Utilization

4. Power Utilization

5. Need of the system/Application

• An arithmetic logic unit (ALU) for processing

• Permanent memory for keeping the program (= ROM)

• Volatile memory for computation (= RAM)

• Rewritable permanent memory for logging, tuning, storing intermediate data (= EEPROM)

• Connectivity to peripherals

• Binary outputs via single chip pins

• Integrated asynchronous and synchronous serial interfaces such as

UART, I2C, RS232, CAN,SPI

What is a Microprocessor ?

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Embedded System Structure(Generic)

Memory

Processor & ASICsA-DSensor

D-A Actuator

General Characteristics of Embedded Systems

• Perform a single task – Usually not general purpose

• Increasingly high performance and real time constrained

• Power, cost and reliability are important considerations

• HW-SW systems– Software is used for more features and flexibility– Hardware (processors, ASICs, memory etc. are used for

performance and security

9

General Characteristics of Embedded Systems (contd.)

ASIPs and ASICs form a significant component

– Adv: customization lower power, cost and enhanced performance

– Disadv: higher development effort (debuggers, compilers etc.) and larger time to market

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ASIC s

Processor Cores

Mem

Analog IO

Digital

HARVARD ARCHITECTURE• Harvard Architecture refers to a memory structure where the processor is connected to two different memory banks via two sets of buses• This is to provide the processor with two distinct data

paths, one for instruction and one for data• Through this scheme, the CPU can read both an instruction and data from the respective memory banks at the same time• This inherent independence increases the throughput

of the machine by enabling it to always prefetch the next instruction

• The cost of such a system is complexity in hardware Commonly used in DSPs

VON-NEUMANN ARCHITECTURE• A Von-Neumann Machine, in contrast to the Harvard Architecture provides one data path (bus) for both instruction and data As a result, the CPU can either be fetching an instruction from memory, or read/writing data to it Other than less complexity of hardware, it allows for using a single, sequential memory.• Today’s processing speeds vastly outpace memory access times, and we employ a very fast but small amount of memory (cache) local to the processor• Modern processors employ a Harvard Architecture to read from two instruction and data caches, when at the same time using a Von-Neumann Architecture to access external memory

Little v/s BIG ENDIAN• Although numbers are always displayed in the same way, they are

not stored in the same way in memory• Big-Endian machines store the most significant byte of data in the lowest memory address• Little-Endian machines on the other hand, store the least

significant byte of data in the lowest memory address• A Little-Endian machine stores 0x12345678 as: ADD+0: 0x78 ADD+1: 0x56 ADD+2: 0x34 ADD+3: 0x12• A Big-Endian machine stores 0x12345678 as: ADD+0: 0x12 ADD+1: 0x34 ADD+2: 0x56 ADD+3: 0x78

8051 Flavors ( AT89c51)

• 4 Kbytes of Flash,

• 128 bytes of RAM,

• 32 I/O lines,

• two 16-bit timer/counters,

• 6 Interrupts

• 5V Vcc

• 40 pin Packaging

Pin Description of the 8051

1234567891011121314151617181920

4039383736353433323130292827262524232221

P1.0P1.1P1.2P1.3P1.4P1.5P1.6P1.7RST

(RXD)P3.0(TXD)P3.1

(T0)P3.4(T1)P3.5

XTAL2XTAL1

GND

(INT0)P3.2(INT1)P3.3

(RD)P3.7(WR)P3.6

VccP0.0(AD0)P0.1(AD1)P0.2(AD2)P0.3(AD3)P0.4(AD4)P0.5(AD5)P0.6(AD6)P0.7(AD7)EA/VPPALE/PROGPSENP2.7(A15)P2.6(A14)P2.5(A13)P2.4(A12)P2.3(A11)P2.2(A10)P2.1(A9)P2.0(A8)

8051(8031)

Figure (a). XTAL Connection to 8051

C2

30pF

C1

30pF

XTAL2

XTAL1

GND

Using a quartz crystal oscillator We can observe the frequency on the XTAL2 pin.

Pins of 8051（ 1/4）

• Vcc （ pin 40 ）：– Vcc provides supply voltage to the chip. – The voltage source is +5V.

• GND （ pin 20 ）： ground• XTAL1 and XTAL2 （ pins 19,18 ）

Pins of 8051（ 2/4）

• RST （ pin 9 ）： reset– It is an input pin and is active high （ normally low ） .

• The high pulse must be high at least 2 machine cycles.

– It is a power-on reset.• Upon applying a high pulse to RST, the

microcontroller will reset and all values in registers will be lost.

• Reset values of some 8051 registers

Pins of 8051（ 3/4）

• /EA （ pin 31 ）： external access

– There is no on-chip ROM in 8031 and 8032 .– The /EA pin is connected to GND to indicate the code is

stored externally.– /PSEN ＆ ALE are used for external ROM.– For 8051, /EA pin is connected to Vcc.– “/” means active low.

• /PSEN （ pin 29 ）： program store enable– This is an output pin and is connected to the OE pin of the

ROM.

Pins of 8051（ 4/4）

• ALE （ pin 30 ）： address latch enable– It is an output pin and is active high.– 8051 port 0 provides both address and data.– The ALE pin is used for de-multiplexing the address

and data by connecting to the G pin of the 74LS373 latch.

• I/O port pins– The four ports P0, P1, P2, and P3.– Each port uses 8 pins.– All I/O pins are bi-directional.

Pins of I/O Port

• The 8051 has four I/O ports– Port 0 （ pins 32-39 ）： P0 （ P0.0 ～ P0.7 ）– Port 1 （ pins 1-8 ） ： P1 （ P1.0 ～ P1.7 ）– Port 2 （ pins 21-28 ）： P2 （ P2.0 ～ P2.7 ）– Port 3 （ pins 10-17 ）： P3 （ P3.0 ～ P3.7 ）– Each port has 8 pins.

• Named P0.X （ X=0,1,...,7 ） , P1.X, P2.X, P3.X• Ex ： P0.0 is the bit 0 （ LSB ） of P0 • Ex ： P0.7 is the bit 7 （ MSB ） of P0• These 8 bits form a byte.

• Each port can be used as input or output (bi-direction).

Other Pins

• P1, P2, and P3 have internal pull-up resisters.– P1, P2, and P3 are not open drain.

• P0 has no internal pull-up resistors and does not connects to Vcc inside the 8051.– P0 is open drain.– Compare the figures of P1.X and P0.X.

• However, for a programmer, it is the same to program P0, P1, P2 and P3.

• All the ports upon RESET are configured as output.

Port 0 with Pull-Up Resistors

P0.0P0.1P0.2P0.3P0.4P0.5P0.6P0.7

DS5000

8751

8951

Vcc10 K

Port 0

Port 3 Alternate Functions

17RDP3.7

16WRP3.6

15T1P3.5

14T0P3.4

13INT1P3.3

12INT0P3.2

11TxDP3.1

10RxDP3.0

PinFunctionP3 Bit

Registers

A

B

R0

R1

R3

R4

R2

R5

R7

R6

DPH DPL

PC

DPTR

PC

Some 8051 16-bit Register

Some 8-bitt Registers of the 8051

SP

Memory mapping in 8051

• ROM memory map in 8051 family

0000H

0FFFH

0000H

1FFFH8751

AT89C51 8752AT89C52

4k 8k

• RAM memory space allocation in the 8051

7FH

30H

2FH

20H

1FH

17H

10H

0FH

07H

08H

18H

00HRegister Bank 0

(Stack ) 1Register Bank

Register Bank 2

Register Bank 3

Bit-Addressable RAM

Scratch pad RAM

Stack in the 8051

• The register used to access the stack is called SP (stack pointer) register.

• The stack pointer in the 8051 is only 8 bits wide, which means that it can take value 00 to FFH. When 8051 powered up, the SP register contains value 07.

7FH

30H

2FH

20H1FH

17H10H

0FH

07H

08H

18H

00HRegister Bank 0

)Stack (Register Bank 1

Register Bank 2

Register Bank 3

Bit-Addressable RAM

Scratch pad RAM

Program Counter• The Program Counter is a 16 or 32 bit register which

contains the address of the next instruction to be executed

• The PC automatically increments to the next sequential memory location every time an instruction is fetched

• Branch, jump, and interrupt operations load the Program Counter with an address other than the next sequential location

• During reset, the PC is loaded from a pre-defined memory location to signify the starting address of the code

RestVector• The significance of the reset vector is that it points the

processor to the memory address which contains the firmware’s first instruction

• Without the Reset Vector, the processor would not know where to begin execution

• Upon reset, the processor loads the Program Counter (PC) with the reset vector value from a pre-defined memory location

• On CPU08 architecture, this is at location $FFFE:$FFFF• A common mistake which occurs during the debug phase

– when reset vector is not necessary – the developer takes it for granted and doesn’t program into the final image. As a

result, the processor doesn’t start up on the final product.

Stack Pointer• The Stack Pointer (SP), much like the reset vector, is

required at boot time for many processors• Some processors, in particular the 8-bit microcontrollers automatically provide the stack

pointer by resetting it to a predefined value• On a higher end processor, the stack pointer is usually

read from a non-volatile memory location, much like the reset vector

• For example on a ColdFire microprocessor, the first sixteen bytes of memory location must be

programmed as follows:• 0x00000000: Reset Vector• 0x00000008: Stack Pointer

Infinite Loop

• Embedded Systems, unlike a PC, never “exit” an application• They idle through an Infinite Loop waiting for an event to happen in the form of an interrupt, or a pre-scheduled task• In order to save power, some processors enter special sleep or wait modes instead of idling through an Infinite Loop, but they will come out of this mode upon either a timer or an External Interrupt

Interrupts

• Interrupts are mostly hardware mechanisms which tell the program an event has occurred• They happen at any time, and are therefore asynchronous to program flow• They require special handling by the processor, and are ultimately handled by a corresponding Interrupt Service Routine (ISR)• Need to be handled quickly. Take too much time servicing an interrupt, and you may miss another interrupt.

Compilation of C file

Source

Preprocessed

SourceASM

O

B

J

E

C

T

.s

.o

Preprocessor Compiler Assembler

LinkerLoader

Executable

a.out

Executable

Program

In Memory

Breaking Down CC

source

Preprocessed

SourceASM

O

B

J

E

C

T

.s

.o

Preprocessor Compiler Assembler

LinkerLoader

Executable

a.out

Executable

Program

In Memory

C Preprocessor (.cpp)

• Pass over source– Insert included files– Perform macro substitutions

• Define macros– #define NUM 100– #define xx(v,name,op,metrics) \ v=xxinit(op,name,IR-

>metrics)

• gcc –E example.c sends preprocessor output to stdout

Breaking Down CC

source

Preprocessed

SourceASM

O

B

J

E

C

T

.s

.o

Preprocessor Compiler Assembler

LinkerLoader

Executable

a.out

Executable

Program

In Memory

Compiler• gcc actually name of a script

• Compiler translates one language to another (or the same???)

• gcc compiler translates C to assembler

• gcc –S example.c “saves” example.s

• Compiler consists of– Parser– Code generation– Mysticism

Breaking Down CC

Source

Preprocessed

SourceASM

O

B

J

E

C

T

.s

.o

Preprocessor Compiler Assembler

LinkerLoader

Executable

a.out

Executable

Program

In Memory

Assembler

• Another translator ??? (as example.s)

• Assembler to (binary) object

• Why not compile straight to binary?

• gcc –c example.c to “save” object

• NM to look at object (nm example.o)

Breaking Down CC

Source

Preprocessed

SourceASM

O

B

J

E

C

T

.s

.o

Preprocessor Compiler Assembler

LinkerLoader

Executable

a.out

Executable

Program

In Memory

Linker

• Combine objects, both user .o files and libraries, make an executable

• gcc *.o –lm yields a.out

• gcc –o myExec *.o –lm

• Use nm to look at object

Breaking Down CC

Source

Preprocessed

SourceASM

O

B

J

E

C

T

.s

.o

Preprocessor Compiler Assembler

LinkerLoader

Executable

a.out

Executable

Program

In Memory

Loader

• Gets an address to place program

• Changes necessary addresses (if any)

• Places code into memory

Project development and an Assembler

Note: Let us assume that assembler and programmer driver is

already installed on PC.

Software tools: Editor, Assembler and EPROM driver

Hardware tools: PC and EPROM programmer

Editor

• It is a software tool, used to create, edit and maintain source file.

• It creates a file in an ASCII file format.

• Different types editors are in existence

• They come with different features. E.g. Refer Notepad features

Assembler• What is an assembler?• Types of assembler –Single Pass & two Pass Assembler• Working on Assemblers – procedure

STEP No1: Go to Command line

Open an Editor

>>edit OR /* It opens a new file with name sample.asm */

>> edit sample.asm /* This is a source a file */

STEP No 2: Create, edit and save a source file.

STEP No 3: Assemble a source file

>> A51 sample.asm /* A51.exe is an assembler */

• It creates various files, e.g. sample.hex, sample.lst etc.

STEP No 4: Open EPROM driver, download binary image to the

target board with the help of EPROM Programmer

EPROM Programmer: Model 1

EPROM Programmer: Model 2

EEPROM Programmer: Model 3

Project development and a Compiler: (x)Note: Assume that a compiler and programmer driver is already

installed on PC.

Software tools: Editor, Compiler and EPROM driver

Hardware tools: PC and EPROM programmer

Project development and an IDE

Integrated Development Environment (IDE):• All software tools discussed earlier, are kept under one common

unified user interface, i.e. IDE

• Becomes possible to make a code change and get the modified

code loaded with a few mouse clicks

• A good IDE allows you for example to click on a syntax error

message produced by the compiler and have the source code with

the highlighted offending instruction pop up for editing in the text

editor

• Some IDEs are flexible enough to allow you to incorporate different

choices of third party tools (like compilers and debuggers), others

only work with a manufacturer's own tool chain.

Debugging tools

• Different types of tools – differ greatly in terms of development time

spend and debugging features available e.g.

- Simulators.

- Microcontroller starter kits.

- Emulator.

Simulators• It tries to model the behavior of the complete microcontroller in

software

• No matter how fast your PC, there is no simulator on the market that can actually simulate a microcontroller's behavior in real-time

• A simulator can also not talk to your target system, so functions that rely on external components are difficult to verify

• For that reason simulators are best suited to test algorithms that run completely within the microcontroller

• They are the perfect tool to complement expensive emulators for large development teams, where buying an emulator for each developer is financially not feasible

Microcontroller Starter Kits:• It consists of:

- Hardware board(Evaluation board).

- In system programmer.

- Some software tools like compiler,assembler, linker etc

- sometimes an IDE and code –size limited evaluation version of a compiler

• A big advantage of these kits over simulators is that they work in

real-time and thus allow for easy input/output functionality

verification.

• Starter kits, however, are completely sufficient and the cheapest

option to develop simple microcontroller projects

Emulators• An emulator is a piece of hardware that ideally behaves exactly like

the real microcontroller chip with all its integrated functionality

• It is the most powerful debugging tool of all

Debug board modules: (DBM)• The "debug board" approach combines all of the emulator

electronics and the actual emulation chip onto a single, larger sized PCB.

Machine Cycle VS Clock Cycle

• 4Mhz to 30 Mhz , our case we will be using 11.0592 Mhz crystal.

• one machine cycle lasts 12 oscillator periods.

• Period of machine cycle = 11.0592/12 = 921.6khz

machine cycle is 1/921.6khz = 1.085us.