Fast and Effective Embedded Systems Design, Second Edition: Applying the ARM mbed

512 Pages·2017·11.58 MB·English

by  Rob Toulson, Tim Wilmshurst

Fast and Effective Embedded
Systems Design

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Fast and Effective Embedded Systems Design

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Fast and Effective Embedded
Systems Design

Applying the ARM mbed

Second Edition

Rob Toulson

Tim Wilmshurst

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Contents

Introduction ..................................................................................................... xv

PART I: Essentials of Embedded Systems, Using the mbed

Chapter 1: Embedded Systems, Microcontrollers, and ARM................................... 3
1.1 Introducing Embedded Systems ............................................................................ 3
1.1.1 What Is an Embedded System?......................................................................... 3
1.1.2 An Example Embedded System........................................................................ 5
1.1.3 A Second Example System: A Word on Control Systems and the Segway ... 6
1.2 Microprocessors and Microcontrollers.................................................................. 8
1.2.1 Some Computer Essentials ................................................................................ 8
1.2.2 The Microcontroller......................................................................................... 10
1.3 Development Processes for Embedded Systems................................................. 11
1.3.1 Programming LanguagesdWhat’s So Special About C/Cþþ? .................... 11
1.3.2 The Development Cycle .................................................................................. 12
1.4 The World of ARM ............................................................................................. 13
1.4.1 A Little History................................................................................................ 13
1.4.2 Some Technical DetaildWhat Does This RISC Word Mean?...................... 15
1.4.3 The Cortex Core .............................................................................................. 16
Chapter Review .......................................................................................................... 17
Quiz............................................................................................................................. 17
References................................................................................................................... 18

Chapter 2: Introducing the mbed....................................................................... 19
2.1 Introducing the mbed........................................................................................... 19
2.1.1 mbed and mbed-Enabled ................................................................................. 19
2.1.2 The mbed LPC1768......................................................................................... 20
2.1.3 The mbed LPC1768 Architecture ................................................................... 21
2.1.4 The LPC1768 Microcontroller ........................................................................ 23
2.2 Getting Started With the mbed: A Tutorial......................................................... 25
Step 1. Connecting the mbed to the PC................................................................... 25
Step 2. Creating an mbed Account........................................................................... 25
Step 3. Running a Program....................................................................................... 26
Step 4. Compiling the Program ................................................................................ 28

v

Step 5. Downloading the Program Binary Code...................................................... 29
Step 6. Modifying the Program Code ...................................................................... 29
2.3 The Development Environment........................................................................... 29
2.3.1 The mbed Software Development Kit and API.............................................. 29
2.3.2 Using C/Cþþ................................................................................................... 30
2.3.3 The mbed Application Board .......................................................................... 30
Chapter Review .......................................................................................................... 33
Quiz............................................................................................................................. 34
References................................................................................................................... 35

Chapter 3: Digital Input and Output................................................................. 37
3.1 Starting to Program.............................................................................................. 37
3.1.1 Thinking About the First Program.................................................................. 37
3.1.2 Using the mbed API ........................................................................................ 40
3.1.3 Exploring the while Loop................................................................................ 41
3.2 Voltages as Logic Values..................................................................................... 42
3.3 Digital Output on the mbed................................................................................. 44
3.3.1 Using Light Emitting Diodes .......................................................................... 44
3.3.2 Using mbed External Pins............................................................................... 46
3.4 Using Digital Inputs............................................................................................. 47
3.4.1 Connecting Switches to a Digital System....................................................... 47
3.4.2 The DigitalIn API ............................................................................................ 48
3.4.3 Using if to Respond to a Switch Input ........................................................... 49
3.5 Digital Input and Output With the Application Board....................................... 51
3.6 Interfacing Simple Optodevices .......................................................................... 54
3.6.1 Optoreflective and Transmissive Sensors........................................................ 54
3.6.2 Connecting an Optosensor to the mbed.......................................................... 55
3.6.3 Seven-Segment Displays.................................................................................. 56
3.6.4 Connecting a Seven-Segment Display to the mbed ....................................... 58
3.7 Switching Larger DC Loads................................................................................ 61
3.7.1 Applying Transistor Switching........................................................................ 61
3.7.2 Switching a Motor With the mbed.................................................................. 63
3.7.3 Switching Multiple Seven-Segment Displays................................................. 64
3.8 Mini Project: Letter Counter ............................................................................... 65
Chapter Review .......................................................................................................... 65
Quiz............................................................................................................................. 65
References................................................................................................................... 67

Chapter 4: Analog Output................................................................................ 69
4.1 Introducing Data Conversion............................................................................... 69
4.1.1 The DAC .......................................................................................................... 69
4.2 Analog Outputs on the mbed............................................................................... 70
4.2.1 Creating Constant Output Voltages................................................................. 71
4.2.2 Saw Tooth Waveforms..................................................................................... 72

Contents

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4.2.3 Testing the DAC Resolution............................................................................ 75
4.2.4 Generating a Sine Wave .................................................................................. 75
4.3 Another Form of Analog Output: Pulse Width Modulation .............................. 76
4.4 Pulse Width Modulation on the mbed ................................................................ 78
4.4.1 Using the mbed Pulse Width Modulation Sources......................................... 78
4.4.2 Some Trial Pulse Width Modulation Outputs................................................. 79
4.4.3 Speed Control of a Small Motor..................................................................... 80
4.4.4 Generating Pulse Width Modulation in Software........................................... 82
4.4.5 Servo Control ................................................................................................... 83
4.4.6 Producing Audio Output.................................................................................. 85
Chapter Review .......................................................................................................... 88
Quiz............................................................................................................................. 88
References................................................................................................................... 89

Chapter 5: Analog Input .................................................................................. 91
5.1 Analog-to-Digital Conversion (ADC) ................................................................. 91
5.1.1 The ADC.......................................................................................................... 91
5.1.2 Range, Resolution, and Quantization.............................................................. 92
5.1.3 Sampling Frequency ........................................................................................ 94
5.1.4 Analog Input With the mbed........................................................................... 95
5.2 Combining Analog Input and Output.................................................................. 96
5.2.1 Controlling LED Brightness by Variable Voltage .......................................... 96
5.2.2 Controlling LED Brightness by PWM............................................................ 98
5.2.3 Controlling PWM Frequency .......................................................................... 99
5.3 Processing Data From Analog Inputs ............................................................... 100
5.3.1 Displaying Values on the Computer Screen ................................................. 100
5.3.2 Scaling ADC Outputs to Recognized Units.................................................. 101
5.3.3 Applying Averaging to Reduce Noise........................................................... 102
5.4 Some Simple Analog Sensors ........................................................................... 103
5.4.1 The Light-Dependent Resistor....................................................................... 103
5.4.2 Integrated Circuit Temperature Sensor ......................................................... 104
5.5 Exploring Data Conversion Timing .................................................................. 105
5.5.1 Estimating Conversion Time and Applying Nyquist.................................... 105
5.6 Mini Projects...................................................................................................... 107
5.6.1 Two-Dimensional Light Tracking ................................................................. 107
5.6.2 Temperature Alarm ........................................................................................ 108
Chapter Review ........................................................................................................ 108
Quiz........................................................................................................................... 108
References................................................................................................................. 109

Chapter 6: Further Programming Techniques ................................................... 111
6.1 The Benefits of Considered Program Design and Structure ............................ 111
6.2 Functions ............................................................................................................ 111
6.3 Program Design.................................................................................................. 112

Contents

vii

6.3.1 Using Flow Charts to Define Code Structure............................................... 112
6.3.2 Pseudocode..................................................................................................... 114
6.4 Working With Functions on the mbed.............................................................. 115
6.4.1 Implementing a Seven-Segment Display Counter........................................ 116
6.4.2 Function Reuse............................................................................................... 118
6.4.3 A More Complex Program Using Functions................................................ 119
6.5 Using Multiple Files in C/Cþþ........................................................................ 121
6.5.1 Summary of the C/Cþþ Program Compilation Process.............................. 122
6.5.2 Using #define, #include, #ifndef, and #endif Directives.............................. 122
6.5.3 Using mbed Objects Globally ....................................................................... 125
6.6 Modular Program Example................................................................................ 125
6.7 Working With Bespoke Libraries...................................................................... 129
Chapter Review ........................................................................................................ 133
Quiz........................................................................................................................... 134
References................................................................................................................. 134

Chapter 7: Starting with Serial Communication ................................................ 135
7.1 Introducing Synchronous Serial Communication ........................................... 135
7.2 SPI .................................................................................................................... 137
7.2.1 Introducing SPI ............................................................................................ 137
7.2.2 SPI on the mbed and Application Board.................................................... 138
7.2.3 Setting Up an mbed SPI Master.................................................................. 138
7.2.4 Creating a SPI Data Link ............................................................................ 140
7.3 Intelligent Instrumentation............................................................................... 144
7.3.1 Introducing the SPI-Linked ADXL345 Accelerometer.............................. 145
7.3.2 Developing a Simple ADXL345 Program.................................................. 145
7.4 Evaluating SPI.................................................................................................. 148
7.5 The I2C Bus ..................................................................................................... 149
7.5.1 Introducing the I2C Bus............................................................................... 149
7.5.2 I2C on the mbed........................................................................................... 151
7.5.3 Setting Up an I2C Data Link....................................................................... 152
7.6 Communicating With I2C-Enabled Sensors.................................................... 155
7.6.1 The TMP102 Sensor.................................................................................... 155
7.6.2 The SRF08 Ultrasonic Range Finder.......................................................... 158
7.7 Evaluating I2C.................................................................................................. 159
7.8 Asynchronous Serial Data Communication .................................................... 160
7.8.1 Introducing Asynchronous Serial Data ....................................................... 160
7.8.2 Applying Asynchronous Communication on the mbed ............................. 161
7.8.3 Applying Asynchronous Communication With the Host Computer.......... 164
7.9 USB .................................................................................................................. 164
7.9.1 Introducing USB ..........................................................................................164
7.9.2 USB Capability on the mbed ...................................................................... 165
7.9.3 Using the mbed to Emulate a USB Mouse ................................................ 166
7.9.4 Leaving USB for Now................................................................................. 167

Contents

viii

7.10 Mini Project: Multinode I2C Bus .................................................................... 167
Chapter Review ........................................................................................................ 167
Quiz........................................................................................................................... 168
References................................................................................................................. 169

Chapter 8: Liquid Crystal Displays.................................................................. 171
8.1 Display Technologies......................................................................................... 171
8.1.1 Introducing Liquid Crystal Technology ........................................................ 171
8.1.2 Liquid Crystal Character Displays ................................................................ 172
8.2 Using the PC1602F LCD................................................................................... 174
8.2.1 Introducing the PC1602F Display................................................................. 174
8.2.2 Connecting the PC1602F to the mbed.......................................................... 175
8.2.3 Using Modular Coding to Interface the LCD............................................... 176
8.2.4 Initializing the Display .................................................................................. 177
8.2.5 Sending Display Data to the LCD ................................................................ 178
8.2.6 The Complete LCD.cpp Definition ............................................................... 180
8.2.7 Using the LCD Functions.............................................................................. 181
8.2.8 Adding Data to a Specified Location............................................................ 182
8.3 Using the mbed TextLCD Library .................................................................... 183
8.4 Displaying Analog Input Data on the LCD...................................................... 185
8.5 Pixel GraphicsdImplementing the NHD-C12832 Display.............................. 187
8.6 Color LCDsdInterfacing the uLCD-144-G2 ................................................... 193
8.7 Mini Project: Digital Spirit Level ..................................................................... 196
Chapter Review ........................................................................................................ 197
Quiz........................................................................................................................... 198
References................................................................................................................. 198

Chapter 9: Interrupts, Timers, and Tasks ........................................................ 199
9.1 Time and Tasks in Embedded Systems........................................................... 199
9.1.1 Timers and Interrupts................................................................................... 199
9.1.2 Tasks............................................................................................................. 199
9.1.3 Event-Triggered and Time-Triggered Tasks ............................................... 200
9.1.4 Working in “Real Time”.............................................................................. 200
9.2 Responding to External Events ....................................................................... 201
9.2.1 Polling .......................................................................................................... 201
9.2.2 Introducing Interrupts .................................................................................. 202
9.3 Simple Interrupts on the mbed........................................................................ 203
9.4 Getting Deeper Into Interrupts ........................................................................ 205
9.4.1 Interrupts on the LPC1768 .......................................................................... 208
9.4.2 Testing Interrupt Latency............................................................................. 208
9.4.3 Disabling Interrupts...................................................................................... 209
9.4.4 Interrupts From Analog Inputs....................................................................210
9.4.5 Conclusion on Interrupts.............................................................................. 211
9.5 An Introduction to Timers............................................................................... 211
9.5.1 The Digital Counter..................................................................................... 212

Contents

ix

9.5.2 Using the Counter as a Timer ..................................................................... 212
9.5.3 Timers on the mbed..................................................................................... 213
9.6 Using the mbed Timer..................................................................................... 213
9.6.1 Using Multiple mbed Timers....................................................................... 214
9.6.2 Testing the Timer Maximum Duration ....................................................... 216
9.7 Using the mbed Timeout ................................................................................. 217
9.7.1 A Simple Timeout Application ................................................................... 217
9.7.2 Further Use of Timeout ............................................................................... 219
9.7.3 Timeout Used to Test Reaction Time ......................................................... 220
9.8 Using the mbed Ticker .................................................................................... 222
9.8.1 Using Ticker for a Metronome.................................................................... 223
9.8.2 Reflecting on Multitasking in the Metronome Program............................. 225
9.9 The Real-Time Clock....................................................................................... 226
9.10 Switch Debouncing.......................................................................................... 226
9.11 Where Do We Go From Here? The Real-Time Operating System............... 229
9.11.1 The Limits of Conventional Programming ............................................... 229
9.11.2 Introducing the Real-Time Operating System .......................................... 230
9.11.3 A Mention of the mbed RTOS.................................................................. 231
9.12 Mini Projects.................................................................................................... 231
9.12.1 A Self-contained Metronome .................................................................... 231
9.12.2 Accelerometer Threshold Interrupt ...........................................................231
Chapter Review ........................................................................................................ 232
Quiz........................................................................................................................... 233
References................................................................................................................. 233

Chapter 10: Memory and Data Management ................................................... 235
10.1 A Memory Review........................................................................................... 235
10.1.1 Memory Types ........................................................................................... 235
10.1.2 Essential Memory Technologies................................................................ 235
10.2 Introducing Pointers......................................................................................... 238
10.3 Using Data Files With the mbed..................................................................... 240
10.3.1 Reviewing Some Useful C/Cþþ Library Functions................................ 241
10.3.2 Defining the mbed Local File System ...................................................... 241
10.3.3 Opening and Closing Files ........................................................................ 242
10.3.4 Recovering a “Lost” mbed ........................................................................ 243
10.3.5 Writing and Reading File Data .................................................................243
10.4 Example mbed Data File Access .................................................................... 244
10.4.1 File Access ................................................................................................. 244
10.4.2 String File Access...................................................................................... 245
10.4.3 Using Formatted Data................................................................................ 246
10.5 Using External SD Card Memory With the mbed ......................................... 247
10.6 Using External USB Flash Memory With the mbed...................................... 250
10.7 Mini Project: Accelerometer Data Logging on Exceeding Threshold........... 252
Chapter Review ........................................................................................................ 253

Contents

x

Quiz........................................................................................................................... 254
References................................................................................................................. 254

PART II: Moving to Advanced and Specialist Applications ................255

Chapter 11: Wireless Communication e Bluetooth and Zigbee........................... 257
11.1 Introducing Wireless Data Communication.................................................... 257
11.1.1 Some Wireless Preliminaries..................................................................... 257
11.1.2 Wireless Networks ..................................................................................... 260
11.1.3 A Word on Protocols.................................................................................. 261
11.2 Bluetooth .......................................................................................................... 263
11.2.1 Introducing Bluetooth ................................................................................ 263
11.2.2 The RN-41 and RN-42 Bluetooth Modules.............................................. 264
11.2.3 Getting to Know the RN-41...................................................................... 265
11.2.4 Simple Bluetooth: Sending mbed Data to a PC....................................... 268
11.2.5 Simple Bluetooth: Receiving Bluetooth Data From a PC ....................... 269
11.2.6 More Advanced Bluetooth: Communicating Between Two mbeds......... 270
11.2.7 Evaluating Bluetooth.................................................................................. 274
11.3 Zigbee............................................................................................................... 274
11.3.1 Introducing Zigbee..................................................................................... 274
11.3.2 Introducing XBee Wireless Modules ........................................................276
11.3.3 Linking to the XBee From a PC............................................................... 277
11.3.4 Configuring an XBee Pair ......................................................................... 279
11.3.5 Implementing a Zigbee Link with XBee and the mbed .......................... 279
11.3.6 Introducing the XBee API......................................................................... 284
11.3.7 Applying the XBee API ............................................................................ 285
11.3.8 Conclusion on Zigbee and Further Work.................................................. 288
11.4 Mini Projects.................................................................................................... 289
11.4.1 Bluetooth Mini Project .............................................................................. 289
11.4.2 Zigbee Mini Project................................................................................... 289
Chapter Review ........................................................................................................ 289
Quiz........................................................................................................................... 290
References................................................................................................................. 290

Chapter 12: Internet Communication and Control............................................. 291
12.1 Introduction to Internet Communication......................................................... 291
12.2 The Ethernet Communication Protocol........................................................... 291
12.2.1 Ethernet Overview ..................................................................................... 291
12.2.2 Implementing Simple mbed Ethernet Communications........................... 292
12.2.3 Ethernet Communication Between mbeds................................................ 295
12.3 Local Area Network Communications With the mbed.................................. 297
12.3.1 Local Area Network Essentials.................................................................297
12.3.2 Using the mbed for Ethernet Network Communications.........................300
12.3.3 Using the mbed as an HTTP File Server.................................................. 303

Contents

xi

12.4 Using Remote Procedure Calls With the mbed.............................................. 305
12.4.1 Controlling mbed Outputs With Remote Procedure Calls....................... 306
12.4.2 Using Remote Procedure Call Variables................................................... 308
12.5 Using the mbed With Wide Area Networks................................................... 309
12.6 The Internet of Things..................................................................................... 313
12.6.1 The Internet of Things Concept ................................................................ 313
12.6.2 Opportunities and Challenges for Internet of Things Systems ................ 316
12.6.3 mbed and the Internet of Things............................................................... 316
Chapter Review ........................................................................................................ 319
Quiz........................................................................................................................... 320
References................................................................................................................. 321

Chapter 13: Working With Digital Audio ........................................................ 323
13.1 An Introduction to Digital Audio.................................................................... 323
13.2 USB MIDI on the mbed .................................................................................. 324
13.2.1 Sending USB MIDI Data From an mbed ................................................. 324
13.2.2 Reading USB MIDI Data on the mbed .................................................... 327
13.3 Digital Audio Processing................................................................................. 330
13.3.1 Input and Output of Digital Audio Data With the mbed.........................330
13.3.2 Signal Reconstruction ................................................................................ 332
13.4 Digital Audio Filtering Example..................................................................... 334
13.4.1 Implementing a Digital Low-Pass Filter on the mbed............................. 336
13.4.2 Digital High-Pass Filter ............................................................................. 339
13.5 Delay/Echo Effect............................................................................................ 340
13.6 Working With Wave Audio Files .................................................................... 342
13.6.1 The Wave Information Header.................................................................. 342
13.6.2 Reading the Wave File Header With the mbed........................................ 345
13.6.3 Reading and Outputting Mono Wave Data............................................... 347
13.7 High-Fidelity Digital Audio With the mbed................................................... 350
13.7.1 Texas Instruments TLV320 Audio Codec and the I2S Protocol .............. 351
13.7.2 Outputting Audio Data From the TLV320 ............................................... 352
13.7.3 High-Fidelity Wave File Player.................................................................356
13.7.4 High-Fidelity Audio Input (Recording) .................................................... 359
13.8 Summary on Digital Audio and Digital Signal Processing............................ 361
13.9 Mini Project: Portable Music Player............................................................... 361
Chapter Review ........................................................................................................ 361
Quiz........................................................................................................................... 362
References................................................................................................................. 362

Chapter 14: Letting Go of the mbed Libraries.................................................. 365
14.1 Introduction: How Much Do We Depend on the mbed API ......................... 365
14.2 Control Register Concepts............................................................................... 366
14.3 Digital Input/Output......................................................................................... 367

Contents

xii

14.3.1 LPC1768 Digital Input/Output Control Registers .................................... 367
14.3.2 A Digital Output Application....................................................................368
14.3.3 Adding a Second Digital Output............................................................... 370
14.3.4 Digital Inputs.............................................................................................. 371
14.4 Getting Deeper Into the Control Registers ..................................................... 373
14.4.1 Pin Select and Pin Mode Registers...........................................................373
14.4.2 Power Control and Clock Select Registers............................................... 375
14.5 Using the DAC................................................................................................. 377
14.5.1 LPC1768 DAC Control Registers ............................................................. 377
14.5.2 A DAC Application ................................................................................... 378
14.6 Using the ADC................................................................................................. 379
14.6.1 LPC1768 ADC Control Registers ............................................................. 380
14.6.2 An ADC Application ................................................................................. 381
14.6.3 Changing ADC Conversion Speed............................................................ 384
14.7 A Conclusion on Using the Control Registers................................................ 386
Chapter Review ........................................................................................................ 386
Quiz........................................................................................................................... 386
References................................................................................................................. 387

Chapter 15: Hardware Insights: Clocks, Resets, and Power Supply .................... 389
15.1 Hardware Essentials......................................................................................... 389
15.1.1 Power Supply and the mbed...................................................................... 389
15.2 Clock Sources and Their Selection ................................................................. 393
15.2.1 Some Clock Oscillator Preliminaries ........................................................393
15.2.2 LPC1768 Clock Oscillators and the mbed Implementation..................... 394
15.2.3 Adjusting the Clock Configuration Register............................................. 396
15.2.4 Adjusting the Phase-Locked Loop ............................................................ 398
15.2.5 Selecting the Clock Source ....................................................................... 401
15.3 Reset ................................................................................................................. 402
15.3.1 Power-On Reset ......................................................................................... 403
15.3.2 Other Sources of Reset.............................................................................. 404
15.4 Toward Low Power.......................................................................................... 405
15.4.1 How Power Is Consumed in a Digital Circuit.......................................... 405
15.4.2 A Word on Cells and Batteries.................................................................. 407
15.5 Exploring mbed Power Consumption ............................................................. 409
15.5.1 LPC1768 Current Consumption ................................................................ 410
15.5.2 Switching Unwanted Things Off! ............................................................. 411
15.5.3 Manipulating the Clock Frequency...........................................................412
15.5.4 LPC1768 Low-Power Modes ....................................................................413
15.6 Getting Serious About Low Power; the M0/M0þ Cores and the
Zero Gecko....................................................................................................... 414
15.6.1 The M0 Cortex Core.................................................................................. 414
15.6.2 The EFM32 Zero Gecko Starter Kit......................................................... 414

Contents

xiii

Chapter Review ........................................................................................................ 416
Quiz........................................................................................................................... 416
References................................................................................................................. 417

Chapter 16: Developing Commercial Products With mbed ................................. 419
16.1 Embedded Systems Design Process ................................................................ 419
16.2 Using mbed-Enabled Platforms in Commercial Products.............................. 422
16.3 Implementing the mbed Architecture on a Bespoke Printed
Circuit Board.................................................................................................... 427
16.4 Programming the LPC1768 Directly............................................................... 428
16.5 Case Study: Irisense Temperature Logger With Touch Screen Display........ 433
16.6 Closing Remarks.............................................................................................. 436
Chapter Review ........................................................................................................ 436
Quiz........................................................................................................................... 437
References................................................................................................................. 437

Appendix A: Some Number Systems ................................................................ 439
Appendix B: Some C Essentials....................................................................... 447
Appendix C: mbed Technical Data................................................................... 467
Appendix D: Parts List .................................................................................. 473
Appendix E: Using a Host Terminal Emulator .................................................. 477
Index........................................................................................................... 483

Contents

xiv