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Embedded.Linux.System.Design.and.Development
1 Introduction ............................................................................................. 1
1.1 History of Embedded Linux....................................................2
1.1.1 Year 1999.....................................................................3
1.1.2 Year 2000.....................................................................4
1.1.3 Year 2001.....................................................................4
1.1.4 Year 2002.....................................................................5
1.1.5 Year 2003.....................................................................6
1.1.6 Year 2004.....................................................................6
1.2 Why Embedded Linux?............................................................7
1.2.1 Vendor Independence.................................................7
1.2.2 Time to Market............................................................8
1.2.3 Varied Hardware Support...........................................8
1.2.4 Low Cost......................................................................8
1.2.5 Open Source................................................................9
1.2.6 Standards (POSIX(R)) Compliance.............................10
1.3 Embedded Linux Versus Desktop Linux..............................10
1.4 Frequently Asked Questions..................................................11
1.4.1 Is Linux Too Large?...................................................11
1.4.2 Is Linux Real-Time Enough?.....................................11
1.4.3 How Can I Protect My Proprietary Software?.........12
1.4.4 Should I Buy a Commercial Embedded
Linux Distribution?.....................................................12
1.4.5 Which Embedded Linux Distribution Do I
Choose?......................................................................12
1.5 Embedded Linux Distributions..............................................13
1.5.1 BlueCat Linux............................................................14
1.5.2 Cadenux.....................................................................15
1.5.3 Denx...........................................................................17
ix
x Embedded Linux System Design and Development
1.5.4 Embedded Debian (Emdebian)................................18
1.5.5 ELinOS (SYSGO).......................................................19
1.5.6 Metrowerks................................................................20
1.5.7 MontaVista Linux.......................................................22
1.5.8 RTLinuxPro(TM).............................................................23
1.5.9 TimeSys Linux............................................................24
1.6 Porting Roadmap....................................................................26
Notes.................................................................................................28
Getting Started ........................................................................................ 29
2
2.1 Architecture of Embedded Linux..........................................29
2.1.1 Real-Time Executive..................................................29
2.1.2 Monolithic Kernels....................................................30
2.1.3 Microkernel................................................................31
2.2 Linux Kernel Architecture......................................................32
2.2.1 Hardware Abstraction Layer (HAL)..........................33
2.2.2 Memory Manager.......................................................33
2.2.3 Scheduler....................................................................34
2.2.4 File System.................................................................35
2.2.5 IO Subsystem.............................................................36
2.2.6 Networking Subsystems............................................36
2.2.7 IPC..............................................................................36
2.3 User Space..............................................................................36
2.4 Linux Start-Up Sequence........................................................41
2.4.1 Boot Loader Phase....................................................42
2.4.2 Kernel Start-Up..........................................................43
2.4.3 User Space Initialization...........................................47
2.5 GNU Cross-Platform Toolchain.............................................48
2.5.1 Building Toolchain....................................................50
2.5.2 Building Toolchain for MIPS....................................55
Board Support Package ......................................................................... 59
3
3.1 Inserting BSP in Kernel Build Procedure.............................60
3.2 The Boot Loader Interface.....................................................62
3.3 Memory Map...........................................................................66
3.3.1 The Processor Memory Map — MIPS Memory
Model..........................................................................67
3.3.2 Board Memory Map..................................................68
3.3.3 Software Memory Map..............................................68
3.4 Interrupt Management............................................................72
3.5 The PCI Subsystem.................................................................77
3.5.1 Uniqueness of PCI Architecture...............................77
3.5.2 PCI Software Architecture.........................................79
Contents xi
3.6 Timers......................................................................................81
3.7 UART.......................................................................................81
3.7.1 Implementing the Console.......................................81
3.7.2 The KGDB Interface.................................................82
3.8 Power Management................................................................83
3.8.1 Hardware and Power Management.........................83
3.8.2 Power Management Standards.................................85
3.8.3 Supporting Processor’s Power-Saving Modes.........86
3.8.4 Unified Driver Framework for Power
Management...............................................................87
3.8.5 Power Management Applications.............................88
Embedded Storage ................................................................................. 89
4
4.1 Flash Map................................................................................89
4.2 MTD—Memory Technology Device......................................91
4.2.1 The MTD Model........................................................91
4.2.2 Flash Chips................................................................92
4.2.3 Flash Disks.................................................................92
4.3 MTD Architecture...................................................................94
mtd_info Data Structure.........................................96
4.3.1
4.3.2 Interface Between MTD Core and Low-Level
Flash Drivers..............................................................96
4.4 Sample MTD Driver for NOR Flash......................................97
4.5 The Flash-Mapping Drivers.................................................106
mtd_info for NOR Flash Chip............106
4.5.1 Filling up
mtd_info for NAND Flash Chip.........108
4.5.2 Filling up
mtd_info..............................................109
4.5.3 Registering
4.5.4 Sample Mapping Driver for NOR Flash................111
4.6 MTD Block and Character Devices.....................................114
4.7 Mtdutils Package...................................................................116
4.8 Embedded File Systems.......................................................116
4.8.1 Ramdisk....................................................................117
4.8.2 RAMFS......................................................................117
4.8.3 CRAMFS (Compressed RAM File System).............117
4.8.4 Journaling Flash File Systems — JFFS and
JFFS2.........................................................................117
4.8.5 NFS — Network File System..................................119
4.8.6 PROC File System....................................................119
4.9 Optimizing Storage Space....................................................120
4.9.1 Kernel Space Optimization.....................................120
4.9.2 Application Space Optimization.............................121
4.9.3 Applications for Embedded Linux.........................122
4.10 Tuning Kernel Memory........................................................124
xii Embedded Linux System Design and Development
5 Embedded Drivers ............................................................................... 127
5.1 Linux Serial Driver................................................................128
5.1.1 Driver Initialization and Start-Up...........................130
5.1.2 Data Transmission...................................................134
5.1.3 Data Reception........................................................134
5.1.4 Interrupt Handler.....................................................134
5.1.5 Terminos Settings....................................................138
5.2 Ethernet Driver.....................................................................138
5.2.1 Device Initialization and Clean-Up........................140
5.2.2 Data Transmission and Reception .........................142
5.3 I2C Subsystem on Linux......................................................144
5.3.1 I2C Bus.....................................................................145
5.3.2 I2C Software Architecture.......................................147
5.4 USB Gadgets.........................................................................152
5.4.1 USB Basics...............................................................153
5.4.2 Ethernet Gadget Driver...........................................158
5.5 Watchdog Timer...................................................................161
5.6 Kernel Modules.....................................................................162
5.6.1 Module APIs............................................................162
5.6.2 Module Loading and Unloading............................164
Notes...............................................................................................164
Porting Applications ............................................................................ 165
6
6.1 Architectural Comparison.....................................................165
6.2 Application Porting Roadmap..............................................166
6.2.1 Decide Porting Strategy..........................................167
6.2.2 Write an Operating System Porting Layer
(OSPL)......................................................................169
6.2.3 Write a Kernel API Driver......................................170
6.3 Programming with Pthreads................................................171
6.3.1 Thread Creation and Exit.......................................172
6.3.2 Thread Synchronization..........................................174
6.3.3 Thread Cancellation................................................180
6.3.4 Detached Threads...................................................181
6.4 Operating System Porting Layer (OSPL).............................182
6.4.1 RTOS Mutex APIs Emulation..................................182
6.4.2 RTOS Task APIs Emulation....................................185
6.4.3 IPC and Timer APIs Emulation..............................191
6.5 Kernel API Driver.................................................................191
6.5.1 Writing User-Space Stubs........................................194
6.5.2 Kapi Driver Implementation...................................195
6.5.3 Using the Kapi Driver.............................................199
Note.................................................................................................200
Contents xiii
7 Real-Time Linux ................................................................................... 201
7.1 Real-Time Operating System...............................................202
7.2 Linux and Real-Time............................................................202
7.2.1 Interrupt Latency.....................................................203
7.2.2 ISR Duration............................................................204
7.2.3 Scheduler Latency....................................................205
7.2.4 Scheduler Duration..................................................207
7.2.5 User-Space Real-Time.............................................209
7.3 Real-Time Programming in Linux.......................................209
7.3.1 Process Scheduling..................................................210
7.3.2 Memory Locking......................................................213
7.3.3 POSIX Shared Memory...........................................223
7.3.4 POSIX Message Queues..........................................225
7.3.5 POSIX Semaphores..................................................232
7.3.6 Real-Time Signals....................................................233
7.3.7 POSIX.1b Clock and Timers...................................241
7.3.8 Asynchronous I/O...................................................246
7.4 Hard Real-Time Linux..........................................................252
7.4.1 Real-Time Application Interface (RTAI).................253
7.4.2 ADEOS......................................................................258
Building and Debugging ...................................................................... 261
8
8.1 Building the Kernel..............................................................263
8.1.1 Understanding Build Procedure.............................265
8.1.2 The Configuration Process......................................266
8.1.3 Kernel Makefile Framework...................................268
8.2 Building Applications...........................................................270
8.2.1 Cross-Compiling Using Configure..........................273
8.2.2 Troubleshooting Configure Script..........................274
8.3 Building the Root File System.............................................275
8.4 Integrated Development Environment................................278
8.4.1 Eclipse......................................................................279
8.4.2 KDevelop.................................................................279
8.4.3 TimeStorm................................................................279
8.4.4 CodeWarrior.............................................................280
8.5 Debugging Virtual Memory Problems................................280
8.5.1 Debugging Memory Leaks......................................282
8.5.2 Debugging Memory Overflows..............................286
8.5.3 Debugging Memory Corruption.............................287
8.6 Kernel Debuggers.................................................................291
8.7 Profiling.................................................................................293
8.7.1 eProf—An Embedded Profiler................................294
8.7.2 OProfile....................................................................300
xiv Embedded Linux System Design and Development
8.7.3 Kernel Function Instrumentation...........................302
Notes...............................................................................................308
Embedded Graphics ............................................................................. 309
9
9.1 Graphics System...................................................................309
9.2 Linux Desktop Graphics—The X Graphics System...........311
9.2.1 Embedded Systems and X......................................312
9.3 Introduction to Display Hardware......................................313
9.3.1 Display System........................................................313
9.3.2 Input Interface.........................................................316
9.4 Embedded Linux Graphics..................................................316
9.5 Embedded Linux Graphics Driver......................................316
9.5.1 Linux Frame Buffer Interface.................................317
9.5.2 Frame Buffer Internals............................................326
9.6 Windowing Environments, Toolkits, and Applications.....328
9.6.1 Nano-X.....................................................................335
9.7 Conclusion.............................................................................340
Notes...............................................................................................340
uClinux ................................................................................................. 341
10
10.1 Linux on MMU-Less Systems...............................................341
10.1.1 Linux Versus uClinux..............................................342
10.2 Program Load and Execution..............................................343
10.2.1 Fully Relocatable Binaries (FRB)............................345
10.2.2 Position Independent Code (PIC)..........................345
10.2.3 bFLT File Format.....................................................346
10.2.4 Loading a bFLT File................................................347
10.3 Memory Management...........................................................358
10.3.1 Heap.........................................................................358
10.3.2 Stack.........................................................................363
10.4 File / Memory Mapping—The Intricacies of mmap( )
in uClinux.............................................................................364
10.5 Process Creation...................................................................365
10.6 Shared Libraries....................................................................367
10.6.1 uClinux Shared Library Implementation
(libN.so)....................................................................367
10.7 Porting Applications to uClinux..........................................370
10.7.1 Creating uClinux Programs.....................................370
10.7.2 Creating Shared Libraries in uClinux.....................371
10.7.3 Using Shared Library in an Application................373
10.7.4 Memory Limitations.................................................375
10.7.5 mmap Limitations....................................................375
10.7.6 Process-Level Limitations........................................375
Contents xv
10.8 XIP—eXecute In Place.........................................................375
10.8.1 Hardware Requirements .........................................377
10.8.2 Software Requirements...........................................378
10.9 Building uClinux Distribution..............................................378
Notes...............................................................................................380
Appendices
Booting Faster ...................................................................................... 383
A
Techniques for Cutting Down Bootloader Initialization.............384
Tuning Kernel for Decreased Boot-Up Time..............................385
Tuning User Space for Decreased Boot-Up Time......................385
Measuring Boot-Up Time..............................................................386
GPL and Embedded Linux ................................................................... 387
B
User-Space Applications................................................................387
Kernel..............................................................................................388
Points to Remember......................................................................389
Notes...............................................................................................390
............................................................................................................ 391
Index
1 Introduction ............................................................................................. 1
1.1 History of Embedded Linux....................................................2
1.1.1 Year 1999.....................................................................3
1.1.2 Year 2000.....................................................................4
1.1.3 Year 2001.....................................................................4
1.1.4 Year 2002.....................................................................5
1.1.5 Year 2003.....................................................................6
1.1.6 Year 2004.....................................................................6
1.2 Why Embedded Linux?............................................................7
1.2.1 Vendor Independence.................................................7
1.2.2 Time to Market............................................................8
1.2.3 Varied Hardware Support...........................................8
1.2.4 Low Cost......................................................................8
1.2.5 Open Source................................................................9
1.2.6 Standards (POSIX(R)) Compliance.............................10
1.3 Embedded Linux Versus Desktop Linux..............................10
1.4 Frequently Asked Questions..................................................11
1.4.1 Is Linux Too Large?...................................................11
1.4.2 Is Linux Real-Time Enough?.....................................11
1.4.3 How Can I Protect My Proprietary Software?.........12
1.4.4 Should I Buy a Commercial Embedded
Linux Distribution?.....................................................12
1.4.5 Which Embedded Linux Distribution Do I
Choose?......................................................................12
1.5 Embedded Linux Distributions..............................................13
1.5.1 BlueCat Linux............................................................14
1.5.2 Cadenux.....................................................................15
1.5.3 Denx...........................................................................17
ix
x Embedded Linux System Design and Development
1.5.4 Embedded Debian (Emdebian)................................18
1.5.5 ELinOS (SYSGO).......................................................19
1.5.6 Metrowerks................................................................20
1.5.7 MontaVista Linux.......................................................22
1.5.8 RTLinuxPro(TM).............................................................23
1.5.9 TimeSys Linux............................................................24
1.6 Porting Roadmap....................................................................26
Notes.................................................................................................28
Getting Started ........................................................................................ 29
2
2.1 Architecture of Embedded Linux..........................................29
2.1.1 Real-Time Executive..................................................29
2.1.2 Monolithic Kernels....................................................30
2.1.3 Microkernel................................................................31
2.2 Linux Kernel Architecture......................................................32
2.2.1 Hardware Abstraction Layer (HAL)..........................33
2.2.2 Memory Manager.......................................................33
2.2.3 Scheduler....................................................................34
2.2.4 File System.................................................................35
2.2.5 IO Subsystem.............................................................36
2.2.6 Networking Subsystems............................................36
2.2.7 IPC..............................................................................36
2.3 User Space..............................................................................36
2.4 Linux Start-Up Sequence........................................................41
2.4.1 Boot Loader Phase....................................................42
2.4.2 Kernel Start-Up..........................................................43
2.4.3 User Space Initialization...........................................47
2.5 GNU Cross-Platform Toolchain.............................................48
2.5.1 Building Toolchain....................................................50
2.5.2 Building Toolchain for MIPS....................................55
Board Support Package ......................................................................... 59
3
3.1 Inserting BSP in Kernel Build Procedure.............................60
3.2 The Boot Loader Interface.....................................................62
3.3 Memory Map...........................................................................66
3.3.1 The Processor Memory Map — MIPS Memory
Model..........................................................................67
3.3.2 Board Memory Map..................................................68
3.3.3 Software Memory Map..............................................68
3.4 Interrupt Management............................................................72
3.5 The PCI Subsystem.................................................................77
3.5.1 Uniqueness of PCI Architecture...............................77
3.5.2 PCI Software Architecture.........................................79
Contents xi
3.6 Timers......................................................................................81
3.7 UART.......................................................................................81
3.7.1 Implementing the Console.......................................81
3.7.2 The KGDB Interface.................................................82
3.8 Power Management................................................................83
3.8.1 Hardware and Power Management.........................83
3.8.2 Power Management Standards.................................85
3.8.3 Supporting Processor’s Power-Saving Modes.........86
3.8.4 Unified Driver Framework for Power
Management...............................................................87
3.8.5 Power Management Applications.............................88
Embedded Storage ................................................................................. 89
4
4.1 Flash Map................................................................................89
4.2 MTD—Memory Technology Device......................................91
4.2.1 The MTD Model........................................................91
4.2.2 Flash Chips................................................................92
4.2.3 Flash Disks.................................................................92
4.3 MTD Architecture...................................................................94
mtd_info Data Structure.........................................96
4.3.1
4.3.2 Interface Between MTD Core and Low-Level
Flash Drivers..............................................................96
4.4 Sample MTD Driver for NOR Flash......................................97
4.5 The Flash-Mapping Drivers.................................................106
mtd_info for NOR Flash Chip............106
4.5.1 Filling up
mtd_info for NAND Flash Chip.........108
4.5.2 Filling up
mtd_info..............................................109
4.5.3 Registering
4.5.4 Sample Mapping Driver for NOR Flash................111
4.6 MTD Block and Character Devices.....................................114
4.7 Mtdutils Package...................................................................116
4.8 Embedded File Systems.......................................................116
4.8.1 Ramdisk....................................................................117
4.8.2 RAMFS......................................................................117
4.8.3 CRAMFS (Compressed RAM File System).............117
4.8.4 Journaling Flash File Systems — JFFS and
JFFS2.........................................................................117
4.8.5 NFS — Network File System..................................119
4.8.6 PROC File System....................................................119
4.9 Optimizing Storage Space....................................................120
4.9.1 Kernel Space Optimization.....................................120
4.9.2 Application Space Optimization.............................121
4.9.3 Applications for Embedded Linux.........................122
4.10 Tuning Kernel Memory........................................................124
xii Embedded Linux System Design and Development
5 Embedded Drivers ............................................................................... 127
5.1 Linux Serial Driver................................................................128
5.1.1 Driver Initialization and Start-Up...........................130
5.1.2 Data Transmission...................................................134
5.1.3 Data Reception........................................................134
5.1.4 Interrupt Handler.....................................................134
5.1.5 Terminos Settings....................................................138
5.2 Ethernet Driver.....................................................................138
5.2.1 Device Initialization and Clean-Up........................140
5.2.2 Data Transmission and Reception .........................142
5.3 I2C Subsystem on Linux......................................................144
5.3.1 I2C Bus.....................................................................145
5.3.2 I2C Software Architecture.......................................147
5.4 USB Gadgets.........................................................................152
5.4.1 USB Basics...............................................................153
5.4.2 Ethernet Gadget Driver...........................................158
5.5 Watchdog Timer...................................................................161
5.6 Kernel Modules.....................................................................162
5.6.1 Module APIs............................................................162
5.6.2 Module Loading and Unloading............................164
Notes...............................................................................................164
Porting Applications ............................................................................ 165
6
6.1 Architectural Comparison.....................................................165
6.2 Application Porting Roadmap..............................................166
6.2.1 Decide Porting Strategy..........................................167
6.2.2 Write an Operating System Porting Layer
(OSPL)......................................................................169
6.2.3 Write a Kernel API Driver......................................170
6.3 Programming with Pthreads................................................171
6.3.1 Thread Creation and Exit.......................................172
6.3.2 Thread Synchronization..........................................174
6.3.3 Thread Cancellation................................................180
6.3.4 Detached Threads...................................................181
6.4 Operating System Porting Layer (OSPL).............................182
6.4.1 RTOS Mutex APIs Emulation..................................182
6.4.2 RTOS Task APIs Emulation....................................185
6.4.3 IPC and Timer APIs Emulation..............................191
6.5 Kernel API Driver.................................................................191
6.5.1 Writing User-Space Stubs........................................194
6.5.2 Kapi Driver Implementation...................................195
6.5.3 Using the Kapi Driver.............................................199
Note.................................................................................................200
Contents xiii
7 Real-Time Linux ................................................................................... 201
7.1 Real-Time Operating System...............................................202
7.2 Linux and Real-Time............................................................202
7.2.1 Interrupt Latency.....................................................203
7.2.2 ISR Duration............................................................204
7.2.3 Scheduler Latency....................................................205
7.2.4 Scheduler Duration..................................................207
7.2.5 User-Space Real-Time.............................................209
7.3 Real-Time Programming in Linux.......................................209
7.3.1 Process Scheduling..................................................210
7.3.2 Memory Locking......................................................213
7.3.3 POSIX Shared Memory...........................................223
7.3.4 POSIX Message Queues..........................................225
7.3.5 POSIX Semaphores..................................................232
7.3.6 Real-Time Signals....................................................233
7.3.7 POSIX.1b Clock and Timers...................................241
7.3.8 Asynchronous I/O...................................................246
7.4 Hard Real-Time Linux..........................................................252
7.4.1 Real-Time Application Interface (RTAI).................253
7.4.2 ADEOS......................................................................258
Building and Debugging ...................................................................... 261
8
8.1 Building the Kernel..............................................................263
8.1.1 Understanding Build Procedure.............................265
8.1.2 The Configuration Process......................................266
8.1.3 Kernel Makefile Framework...................................268
8.2 Building Applications...........................................................270
8.2.1 Cross-Compiling Using Configure..........................273
8.2.2 Troubleshooting Configure Script..........................274
8.3 Building the Root File System.............................................275
8.4 Integrated Development Environment................................278
8.4.1 Eclipse......................................................................279
8.4.2 KDevelop.................................................................279
8.4.3 TimeStorm................................................................279
8.4.4 CodeWarrior.............................................................280
8.5 Debugging Virtual Memory Problems................................280
8.5.1 Debugging Memory Leaks......................................282
8.5.2 Debugging Memory Overflows..............................286
8.5.3 Debugging Memory Corruption.............................287
8.6 Kernel Debuggers.................................................................291
8.7 Profiling.................................................................................293
8.7.1 eProf—An Embedded Profiler................................294
8.7.2 OProfile....................................................................300
xiv Embedded Linux System Design and Development
8.7.3 Kernel Function Instrumentation...........................302
Notes...............................................................................................308
Embedded Graphics ............................................................................. 309
9
9.1 Graphics System...................................................................309
9.2 Linux Desktop Graphics—The X Graphics System...........311
9.2.1 Embedded Systems and X......................................312
9.3 Introduction to Display Hardware......................................313
9.3.1 Display System........................................................313
9.3.2 Input Interface.........................................................316
9.4 Embedded Linux Graphics..................................................316
9.5 Embedded Linux Graphics Driver......................................316
9.5.1 Linux Frame Buffer Interface.................................317
9.5.2 Frame Buffer Internals............................................326
9.6 Windowing Environments, Toolkits, and Applications.....328
9.6.1 Nano-X.....................................................................335
9.7 Conclusion.............................................................................340
Notes...............................................................................................340
uClinux ................................................................................................. 341
10
10.1 Linux on MMU-Less Systems...............................................341
10.1.1 Linux Versus uClinux..............................................342
10.2 Program Load and Execution..............................................343
10.2.1 Fully Relocatable Binaries (FRB)............................345
10.2.2 Position Independent Code (PIC)..........................345
10.2.3 bFLT File Format.....................................................346
10.2.4 Loading a bFLT File................................................347
10.3 Memory Management...........................................................358
10.3.1 Heap.........................................................................358
10.3.2 Stack.........................................................................363
10.4 File / Memory Mapping—The Intricacies of mmap( )
in uClinux.............................................................................364
10.5 Process Creation...................................................................365
10.6 Shared Libraries....................................................................367
10.6.1 uClinux Shared Library Implementation
(libN.so)....................................................................367
10.7 Porting Applications to uClinux..........................................370
10.7.1 Creating uClinux Programs.....................................370
10.7.2 Creating Shared Libraries in uClinux.....................371
10.7.3 Using Shared Library in an Application................373
10.7.4 Memory Limitations.................................................375
10.7.5 mmap Limitations....................................................375
10.7.6 Process-Level Limitations........................................375
Contents xv
10.8 XIP—eXecute In Place.........................................................375
10.8.1 Hardware Requirements .........................................377
10.8.2 Software Requirements...........................................378
10.9 Building uClinux Distribution..............................................378
Notes...............................................................................................380
Appendices
Booting Faster ...................................................................................... 383
A
Techniques for Cutting Down Bootloader Initialization.............384
Tuning Kernel for Decreased Boot-Up Time..............................385
Tuning User Space for Decreased Boot-Up Time......................385
Measuring Boot-Up Time..............................................................386
GPL and Embedded Linux ................................................................... 387
B
User-Space Applications................................................................387
Kernel..............................................................................................388
Points to Remember......................................................................389
Notes...............................................................................................390
............................................................................................................ 391
Index