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CTask
A Multitasking Kernel for C
Version 2.2 Released 90-10-12
Public Domain Software written by
Thomas Wagner
Ferrari electronic GmbH
Contents
About this Manual 1
Introduction 2
An Example 2
Switching the Context 2
You have Mail 3
Reentrancy and Resources 3
DOS Access 4
Handling the Keyboard 4
Serial I/O and Timeouts 5
Priorities 5
Change to your liking 5
General Notes 7
What can CTask NOT be used for? 7
What is required to use CTask? 7
Do I have to pay for using CTask? 8
What support can I expect? 9
About this Release 10
Multitasking Basics 11
Tasks 11
Events 11
Reentrancy 12
Deadlocks 13
Using CTask 15
Configuration Options 15
Memory Allocation 21
Snapshot 21
Task Stacks 22
Drivers 22
Things to remember 23
Priority Handling 23
Multitasking and DOS 25
Spawning and CTask TSR's 26
Task Groups 27
How does CTask work 29
Queues 29
The Scheduler 30
Events 30
Resources 30
Flags 31
Counters 31
Mailboxes and Pipes 31
Serial and Printer Drivers 32
Ctask Manual - Version 2.2 - 90-10-12 - Contents 1
CTask Data Types 34
Other definitions 35
Typedefs used for simplified type specifications 36
Error return values for event wait functions 37
Queues 37
The timer/watch/hotkey control block 38
The name link structure 43
The task control block structure 43
Task states 46
Task flags 47
The Group Control Block 48
The event control blocks 49
The Ticker structure 49
The flag event structure 50
The counter event structure 50
The resource event structure 51
The mailbox event structure 51
The pipe and word pipe event structure 51
The buffer event structure 52
The call chain structure 53
CTask Routines 54
Global Variables 54
Installation and Removal 54
Searching for names 57
Adding names 58
Remove Functions 58
Preemption and Scheduling 59
Miscellaneous 60
Task Operations 62
Timer Operations 64
Event wait Timeouts 65
"Tickers" 65
Delays 66
Timed Events, Watch Events, and Hotkeys 66
Event Operations 75
Resources 75
Flags 77
Counters 79
Mailboxes 81
Pipes 83
Buffers 86
The Keyboard Handler 88
The Serial I/O handler 88
The Printer Output Driver 94
Support Modules 96
Memory Allocation Interface 96
Printf replacements 97
Snapshot Dump 100
Ctask Manual - Version 2.2 - 90-10-12 - Contents 2
Advanced Topics 101
Primary and Secondary Kernels 101
TSR, Spawning, and EMS 104
Functions called by Kernel Routines 105
Some notes on potential trouble spots 107
Turbo C console output 107
The timer tick EOI 107
Debugging 108
Changes from Previous Versions 109
Changes for CTask 2.1 to 2.2 109
Version 2.2 Interface Changes 111
Changes for CTask 2.0 to 2.1 112
Version 2.1 Interface Changes 115
Changes for CTask 1.2 to 2.0 116
Version 2.0 Interface Changes 116
Changes for CTask 1.1b to 1.2 118
Changes for CTask 1.1 to 1.1b 120
Changes for CTask 0.1 to 1.1 120
Ctask Manual - Version 2.2 - 90-10-12 - Contents 3
About this Manual
If you are new to CTask, I would suggest reading all chapters
before attempting to build your first application. One chapter
you can skip is the CTask Data Types section, since you are not
required to know about the innards of CTask's structures. You can
also ignore the List of Changes.
If you are updating from version 2.0, read the List of Changes,
and the new Advanced Topics section. The chapters on Data Types
and Routines, and the Using CTask section, also contain new
information. All other chapters are basically unchanged.
Version 2.1 users will find little new information here. The
changes in the data structures, and the new routines, are
reflected here, but if you're short on paper, it should be
sufficient to print just the list of changes.
If you are updating from an older release, the List of Changes at
the end is for you. You can safely skip the Introduction, and the
section on Multitasking Basics. In the General Notes, you should
read the section on support and the info about this release. In
the Using CTask section, check the new configuration options, and
the chapter on Memory Allocation. Check the Routine descriptions,
and, if you are using internal data structures directly, the Data
Type descriptions, for changes. The Advanced Topics section is
new.
Finally, a note to German speaking readers:
Dieses Handbuch, wie auch die Kommentare im Quellcode, ist in
Englisch abgefa醫(yī), da dies die universelle Sprache f乺 Computer-
benutzer weltweit ist. Es gibt keine deutsche Version, und es
wird voraussichtlich auch keine geben (sofern nicht jemand bereit
ist einen angemessenen Betrag f乺 eine 歜ersetzung auf den Tisch
des Hauses zu legen). Selbstverst刵dlich bleibt es Ihnen
unbenommen, das Handbuch selbst zu 乥ersetzen und diese Version
auch zu vertreiben, oder mir zum Vertrieb anzubieten. Wie die
Software ist auch dieses Handbuch Public Domain.
Ctask Manual - Version 2.2 - 90-10-12 - Page 1
Introduction
CTask is a set of routines that allow your C program to execute
functions in parallel, without you having to build in sophisti-
cated polling and switching schemes. CTask handles the switching
of processor time with a priority based, preemptive scheduler,
and provides a fairly complete set of routines for inter-task
communication, event signalling, and task interlocking. CTask
also includes a number of drivers for MS-DOS that build on the
basic functions to allow you to include serial I/O, printer
buffering, and concurrent access to DOS functions into your
programs with little programming effort.
An Example
To illustrate one possible use of CTask, let me elaborate on the
following example. Say you just finished your nifty telecommuni-
cations program, complete with download protocols, scripts, and
everything. But wouldn't it be nice to be able to print the file
you just downloaded while receiving the next, and edit a comment
to some previous message without interrupting the transmission?
So you take those editor routines from a previous project, plug
them in, and - oops, how do you switch back and forth between
editing, communication and printing? The answer to this is CTask.
CTask allows your C program to do many different things at the
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