Introduction to ARM and Embedded System

Development tools

By

Nagarathna Yelluri

Application Engineer

VLSI & Embedded Systems Group

Unistring Tech Solutions Pvt. Ltd# D10, 5th Floor, Eureka court, Beside Image hospitals, Ameerpet,

Hyderabad, ph:040-23732798, 09440318188

www.unistring.com

String Technologies#309, Vederi complex, opp Dilshuk Nagar bus Depot, Dilsukh nagar, Hyderabad,

ph: 040 – 24151900

www.stringtechnologies.net

What Is An Embedded System?

A special purpose system with a suitable hardware and software to meet a specific requirement/Application.

Examples:

Mobile phone, keyboard, mouse, car speed

indicator, electronic watch, GPS receiver unit

Where do we find embedded systems?

Automobile

Communication

Avionics

Embedded

Consumer Electronics

Household Appliances

Office Equipments

Embedded

System

Embedded System General Block Diagram

Choices for processor architecture

CISC - Complex Instruction Set Computer

Many instructions which can perform involved operations: compact

code

Can be many clock cycles per instruction

Large silicon area > Higher cost per die

RISC - Reduced Instruction Set Computer

More modern architecture

One instruction executed per clock cycle > Very fastOne instruction executed per clock cycle > Very fast

DSP - Digital Signal Processor

Specialized type of uP

Designed for real time mathematical manipulation of data streams

Radar image processing, audio/voice processing, ultrasound and

photographic image processing

Includes instructions designed for multiplication and accumulation

Choice can be one of the three or a combination

Microprocessor and Microcontroller

Microprocessor

An integrated circuit which forms the central processing unit for a

computer or embedded controller, but requires additional support

circuitry to function

MC68000, 80486, Pentium, K6, etc.

MicrocontrollerMicrocontroller

A microprocessor plus additional peripheral support devices integrated

into a single package

Peripheral support devices may include:

Serial ports ( COM ), Parallel ( Ports ), Ethernet ports, A/D & D/A

Interval timers, watchdog timers, event counter/timers, real time clock

Other local processors ( DSP, numeric coprocessor, peripheral controller )

Intel 8051, ARM, PIC etc

History of ARM

�ARM- Advanced RISC Machine.

�The first processor in ARM family was developed at Acorn Computers Ltd between October 1983 and April 1985. October 1983 and April 1985.

�Now, ARM company is considered to be market dominant in the field of mobile phone chips, due to its power saving features

�We have several other basic microcontroller

families such as PIC, M68HCXX, AVR etc.

�All these basic microcontrollers are useful for

implementing basic interfacing and control

mechanism for simple applications.

Where ARM is used?

mechanism for simple applications.

�There are several applications which require lot

of computation and high speed data processing.

In such applications advanced microcontrollers

and microprocessors are used such as ARM and

SHARC.

ARM Powered Products

Why is ARM popular?

�ARM is widely used in embedded systems because of its power saving feature.

�ARM CPUs are dominant in the �ARM CPUs are dominant in the mobile electronics market, where low power consumption is critical design goal.

ARM Families

ARM7M strongARM

Multiple instructions

Load and store

instructions

ARM7TDMI

ARM and

Thumb modes

ARM1

26 Bit Addressing

ARM2

32 Bit multiplier

32 Bit

coprocessor

ARM3

On chip

cache

ARM6 & ARM7DI

32 Bit addressing

Features of ARM

ARM is popular with developers due to

�Thumb mode of operation.

�A load – store architecture.

�Fixed length 32-bit instructions.�Fixed length 32-bit instructions.

�3-Address instruction format.

�Large 16 word 32 bit register file.

�Orthogonal instruction set.

�Single cycle execution and many more

LPC2148 (ARM) architectures

The ARM architecture

RISC + additional features

Occupies almost 75% of 32bit embedded RISC microprocessor market

Additional features of ARM

Auto-increment/decrement addressing modes

Single data-processing instruction can perform both ALU and shifter operations

Load/Store multiple instruction

Conditional execution

Block

Diagram

LPC2184LPC2184

Processor Operating States

� The ARM7TDMI processor has two operating states:

– ARM - 32-bit, word-aligned ARM instructions are

executed in this state.

– Thumb -16-bit, half word-aligned Thumb

instructions are executed in this state.

� The operating state of the ARM7TDMI core can be

switched between ARM state and Thumb state using

the BX (branch and exchange) instructions.

Processor Modes

ARM has seven operating modes

User unprivileged mode under which most applications run

FIQ entered, when a high priority (fast) interrupt is raised

IRQ general purpose interrupt handling

Supervisor protected mode for the operating systemSupervisor protected mode for the operating system

entered on reset or software interrupt instruction

System privileged mode using same registers as user mode

Abort used to handle memory access violations

Undefined used to handle undefined instructions

The Memory System

• 4 G address space– 8-bit bytes, 16-bit half-words, 32-bit words

– Support both little-endian and big-endian

20212223

bit 31 bit 0

half-word4

word16

0123

4567

891011

byte0

byte

12131415

16171819

byte1byte2

half-word14

byte3

byte6

address

half-word12

word8

Word, half word and byte views

0x0000001C 0x0000000E 0x00000007

6B25 9D0x00000018 0x0000000C 0x00000006

4E87 960x00000014 0x0000000A 0x00000005

1939 6E0x00000010 0x00000008 0x00000004

10 25 6B<62 9D49 A60x0000000C 0x00000006 0x00000003

4E 39 1987 6E96 890x00000008 0x00000004 0x00000002

9D 96 6E49 89A6 2B0x00000004 0x00000002 0x00000001

89 2B 3CA6 3C2B 3C0x00000000 0x00000000 0x00000000

(a) Word view (b) Half word view (c) Byte view

Registers

� 37 registers31 general 32 bit registers, including PC

6 status registers

15 general registers (R0 to R14), and one status registers and program

counter are visible at any time – when you write user-level programs

�The visible registers depend on the processor mode

�The other registers (the banked registers) are switched in

to support IRQ, FIQ, Supervisor, Abort and Undefined

mode processing

Register Bank

Indicates that the normal register used by User or System mode has been replaced by an alternative register specific to the exception mode

Cond…

�R0 to R15 are directly accessible

�R0 to R14 are general purpose

�R13: Stack point (sp) (in common)

�Individual stack for each processor mode

�R14: Linked register (lr)

�R15 holds the Program Counter (PC)

�CPSR - Current Program Status Register contains condition code flags and the current mode bits

�5 SPSRs (Saved Program Status Registers) which are loaded with CPSR when an exceptions occurs

When the processor is executing in ARM state:All instructions are 32 bits in length

All instructions must be word aligned

Therefore the PC value is stored in bits [31:2] with bits [1:0] equal to zero

(as instruction cannot be halfword or byte aligned).

R14 is used as the subroutine link register (LR) and stores

The Program Counter (R15)

R14 is used as the subroutine link register (LR) and stores

the return address when Branch with Link (BL)

operations are performed, calculated from the PC.

Thus to return from a linked branchMOV r15,r14

MOV pc,lr

Program Status Registers - 1

The ARM7TDMI contains a Current Program Status

Register (CPSR), plus five Saved Program Status

Registers (SPSRs) for use by exception handlers.

These register’s functions are:These register’s functions are:

Hold information about the most recently performed ALU operation.

Control the enabling and disabling of interrupts.

Set the processor operating mode

Program Status Registers - 2

The N, Z, C and V are condition code flags

may be changed as a result of arithmetic and logical operations in the

processor

may be tested by all instructions to determine if the instruction is to be

executed

N : Negative. Z : Zero. C : Carry. V : oVerflow

The I and F bits are the interrupt disable bitsThe I and F bits are the interrupt disable bits

The M0, M1, M2, M3 and M4 bits are the mode bits

How Microcontroller Works

�Is Powering the Microcontroller is enough?

�Why the Programmability Feature?

�What is instruction?�What is instruction?

�Where does the Instructions Stores?

�Instruction Fetching & Decoding

�Fixed Set of instructions & Uniqueness

Advantage of Assembly Language

�Improved readability of program

�Ease of debugging

�Speed - Faster running code with assembly

�Some low-level programming is actually �Some low-level programming is actually easier to do with assembly

�Few embedded systems are also programmed in assembly to utilize limited computational resources.

Instruction Format

[Label:] Mnemonic [Operands] [;Comment][Label:] Mnemonic [Operands] [;Comment]

add r1, r2, r3, lsl #4

sub r1, r2, r3, lsl #4

adds r1, r2, r3, lsl #4

Sample Assembly Language Program

adds r1, r2, r3, lsl #4

subs r1, r2, r3, lsl #4

.end

Issues in Assembly programming

�Size of each instruction (in bytes)

�Execution time of each instruction

�Supported addressing modes for each �Supported addressing modes for each instruction

PROGRAMMING IN C

• Why C?

• Easier and less time consuming

• C is easier to modify

• Portability• Portability

• How can processor understand C language?

• What is Compiler & Cross Compiler?

C for Microcontrollers

Of higher level languages, C is the closest to

assembly languages

bit manipulation instructions

pointers (indirect addressing)

Most microcontrollers have available C

compilers

Writing in C simplifies code development for

large projects.

System development scheme

Initialization

• When a C program is compiled, some code

is created that runs BEFORE the main

program.

• This code clears RAM to zero and

initializes your variables. Here is a segment initializes your variables. Here is a segment

of this code: LJMP 0003h

0003: MOV R0, #7FH

CLR A

back: MOV @R0, A

DJNZ R0, back

...

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