Realtime Operating Systems

Concepts and Implementation of Microkernels

for Embedded Systems

Dr. Jürgen Sauermann, Melanie Thelen

2

Contents

	List of Figures.............................................................................	v
	List of Tables .............................................................................	vi
	Preface ........................................................................................	1
1	Requirements ..............................................................................	3
1.1	General Requirements .................................................................................	3
1.2	Memory Requirements ................................................................................	3
1.3	Performance.................................................................................................	4
1.4	Portability ....................................................................................................	5
2	Concepts .....................................................................................	7
2.1	Specification and Execution of Programs....................................................	7
2.1.1	Compiling and Linking ...............................................................................	7
2.2	Loading and Execution of Programs .........................................................	11
2.3	Preemptive Multitasking............................................................................	12
2.3.1	Duplication of Hardware ...........................................................................	12
2.3.2	Task Switch ...............................................................................................	14
2.3.3	Task Control Blocks ..................................................................................	16
2.3.4	De-Scheduling ...........................................................................................	19
2.4	Semaphores ...............................................................................................	21
2.5	Queues .......................................................................................................	26
2.5.1	Ring Buffers ..............................................................................................	26
2.5.2	Ring Buffer with Get Semaphore ..............................................................	28
2.5.3	Ring Buffer with Put Semaphore ..............................................................	29
2.5.4	Ring Buffer with Get and Put Semaphores ...............................................	30
3	Kernel Implementation .............................................................	33
3.1	Kernel Architecture ...................................................................................	33
3.2	Hardware Model ........................................................................................	34
3.2.1	Processor ...................................................................................................	34
3.2.2	Memory Map .............................................................................................	35
3.2.3	Peripherals .................................................................................................	35
3.2.4	Interrupt Assignment .................................................................................	36
3.2.5	Data Bus Usage .........................................................................................	36
3.3	Task Switching ..........................................................................................	39
3.4	Semaphores ...............................................................................................	46
3.4.1	Semaphore Constructors............................................................................	46

ii

3.4.2	Semaphore Destructor ...............................................................................	46
3.4.3	Semaphore P() ...........................................................................................	46
3.4.4	Semaphore Poll() .......................................................................................	48
3.4.5	Semaphore V() ..........................................................................................	49
3.5	Queues .......................................................................................................	51
3.5.1	Ring Buffer Constructor and Destructor ...................................................	51
3.5.2	RingBuffer Member Functions..................................................................	52
3.5.3	Queue Put and Get Functions ....................................................................	53
3.5.4	Queue Put and Get Without Disabling Interrupts......................................	53
3.6	Interprocess Communication.....................................................................	54
3.7	Serial Input and Output .............................................................................	59
3.7.1	Channel Numbers ......................................................................................	62
3.7.2	SerialIn and SerialOut Classes and Constructors/Destructors ..................	63
3.7.3	Public SerialOut Member Functions .........................................................	65
3.7.4	Public SerialIn Member Functions............................................................	69
3.8	Interrupt Processing...................................................................................	71
3.8.1	Hardware Initialization ..............................................................................	71
3.8.2	Interrupt Service Routine ..........................................................................	73
3.9	Memory Management ...............................................................................	77
3.10	Miscellaneous Functions ...........................................................................	79
3.10.1Miscellaneous Functions in Task.cc .........................................................		79
3.10.2Miscellaneous Functions in os.cc .............................................................		80
4	Bootstrap...................................................................................	81
4.1	Introduction ...............................................................................................	81
4.2	System Start-up .........................................................................................	81
4.3	Task Start-up..............................................................................................	87
4.3.1	Task Parameters .........................................................................................	87
4.3.2	Task Creation.............................................................................................	89
4.3.3	Task Activation ..........................................................................................	92
4.3.4	Task Deletion.............................................................................................	92
5	An Application .........................................................................	95
5.1	Introduction ...............................................................................................	95
5.2	Using the Monitor .....................................................................................	95
5.3	A Monitor Session.....................................................................................	98
5.4	Monitor Implementation.........................................................................	102
6	Development Environment .....................................................	107
6.1	General ....................................................................................................	107
6.2	Terminology ............................................................................................	107
6.3	Prerequisites ............................................................................................	109

.	iii

6.3.1	Scenario 1: UNIX or Linux Host ............................................................	109
6.3.2	Scenario 2: DOS Host .............................................................................	110
6.3.3	Scenario 3: Other Host or Scenarios 1 and 2 Failed................................	110
6.4	Building the Cross-Environment .............................................................	112
6.4.1	Building the GNU cross-binutils package...............................................	112
6.4.2	Building the GNU cross-gcc package .....................................................	113
6.4.3	The libgcc.a library..................................................................................	114
6.5	The Target Environment ..........................................................................	117
6.5.1	The Target Makefile.................................................................................	117
6.5.2	The skip_aout Utility...............................................................................	121
7	Miscellaneous .........................................................................	123
7.1	General ....................................................................................................	123
7.2	Porting to different Processors ................................................................	123
7.2.1	Porting to MC68000 or MC68008 Processors ........................................	123
7.2.2	Porting to Other Processor families.........................................................	124
7.3	Saving Registers in Interrupt Service Routines.......................................	125
7.4	Semaphores with time-out.......................................................................	127
A	Appendices .............................................................................	130
A.1	Startup Code (crt0.S) ..............................................................................	130
A.2	Task.hh ....................................................................................................	137
A.3	Task.cc ....................................................................................................	140
A.4	os.hh .......................................................................................................	143
A.5	os.cc ........................................................................................................	145
A.6	Semaphore.hh .........................................................................................	150
A.7	Queue.hh .................................................................................................	151
A.8	Queue.cc .................................................................................................	153
A.9	Message.hh .............................................................................................	157
A.10	Channels.hh ............................................................................................	158
A.11	SerialOut.hh ............................................................................................	159
A.12	SerialOut.cc ............................................................................................	160
A.13	SerialIn.hh ..............................................................................................	166
A.14	SerialIn.cc ...............................................................................................	167
A.15	TaskId.hh ................................................................................................	170
A.16	duart.hh ...................................................................................................	171
A.17	System.config .........................................................................................	175
A.18	ApplicationStart.cc .................................................................................	176
A.19	Monitor.hh ..............................................................................................	177
A.20	Monitor.cc ...............................................................................................	178
A.21	Makefile ..................................................................................................	187
A.22	SRcat.cc ..................................................................................................	189

iv

Index .......................................................................................

201

List of Figures

Figure 2.1	Hello.o Structure ......................................................................................................	8
Figure 2.2	libc.a Structure..........................................................................................................	9
Figure 2.3	Hello Structure .......................................................................................................	10
Figure 2.4	Program Execution .................................................................................................	13
Figure 2.5	Parallel execution of two programs ........................................................................	13
Figure 2.6	Clock ......................................................................................................................	14
Figure 2.7	Task Switch ............................................................................................................	15
Figure 2.8	Shared ROM and RAM ..........................................................................................	16
Figure 2.9	Final Hardware Model for Preemptive Multitasking .............................................	17
Figure 2.10	Task Control Blocks and CurrentTask....................................................................	18
Figure 2.11	Task State Machine.................................................................................................	21
Figure 2.12	P() and V() Function Calls .....................................................................................	24
Figure 2.13	Ring Buffer .............................................................................................................	27
Figure 2.14	Serial Communication between a Task and a Serial Port.......................................	30
Figure 3.1	Kernel Architecture ................................................................................................	33
Figure 3.2	Data Bus Contention ..............................................................................................	36
Figure 3.3	Modes and Interrupts vs. Time ...............................................................................	40
Figure 3.4	Exception Stack Frame...........................................................................................	42
Figure 3.5	Serial Router (Version A) .......................................................................................	59
Figure 3.6	Serial Router (Version B) .......................................................................................	60
Figure 3.7	Serial Router (Version C) .......................................................................................	61
Figure 4.1	??? .DATA and .TEXT during System Start-Up ??? ........	81
Figure 5.1	Monitor Menu Structure .........................................................................................	96
Figure 7.1	Task State Machine...............................................................................................	127
Figure 7.2	Task State Machine with new State S_BLKD......................................................	128