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<a name="1204411"> </a><font color="#003366" face="Verdana, Arial, Helvetica, sans-serif">1 Introduction</font>
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<a name="1204412"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">Multi-tasking is widely accepted as an optimal method of implementing real-time systems. Applications may be broken down into a number of independent tasks which co-ordinate their use of shared system resources such as memory and CPU time. External events arriving from peripheral devices are made known to the system via interrupts.</font>
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<a name="1204416"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The OS20 real-time kernel provides comprehensive multi-tasking services. Tasks synchronize their activities and communicate with each other via semaphores and message queues. Real-world events are handled via interrupt routines and communicated to tasks using semaphores. Memory allocation for tasks is selectively managed by OS20 or the user and tasks may be given priorities and are scheduled accordingly. Timer functions are provided to implement time and delay functions.</font>
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<a name="1204423"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The OS20 real-time kernel is common across all ST20 microprocessors, facilitating the portability of code. The kernel is re-implemented for each core, taking advantage of chip-specific features to produce a highly efficient multi-tasking environment for embedded systems developed for the ST20.</font>
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<a name="1204424"> </a><font size=2 face="Verdana, Arial, Helvetica, sans-serif">The API (Application Programming Interface) defined in this document corresponds to the 2.10 version of OS20.</font>
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<font size=1 face="Verdana, Arial, Helvetica, sans-serif"> © 2001, 2002, 2003 STMicroelectronics. All Rights Reserved.<br>
ADCS 7473749B</font>
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