RTEMS 4.9.2 On-Line Library

Initialization Manager Initializing RTEMS

RTEMS C User's Guide

4.3.1: Initializing RTEMS

The Initialization Manager directives are called by the Board Support Package framework as part of its initialization sequence. RTEMS assumes that the Board Support Package successfully completed its initialization activities. These directives initialize RTEMS by performing the following actions:

Initializing internal RTEMS variables;
Allocating system resources;
Creating and starting the Idle Task;
Initialize all device drivers;
Creating and starting the user initialization task(s); and
Initiating multitasking.

The initialization directives MUST be called in the proper sequence before any blocking directives may be used. The services in this manager should be invoked just once per application and in precisely the following order:

rtems_initialize_data_structures
rtems_initialize_before_drivers
rtems_initialize_device_drivers
rtems_initialize_start_multitasking

It is recommended that the Board Support Package use the provided framework which will invoke these services as part of the executing the function boot_card in the file c/src/lib/libbsp/shared/bootcard.c. This framework will also assist in allocating memory to the RTEMS Workspace and C Program Heap and initializing the C Library.

The effect of calling any blocking RTEMS directives before rtems_initialize_start_multitasking is unpredictable but guaranteed to be bad. After the directive rtems_initialize_data_structures is invoked, it is permissible to allocate RTEMS objects and perform non-blocking operations. But the user should be distinctly aware that multitasking is not available yet and they are NOT executing in a task context.

Many of RTEMS actions during initialization are based upon the contents of the Configuration Table. For more information regarding the format and contents of this table, please refer to the chapter Configuring a System.

The final step in the initialization sequence is the initiation of multitasking. When the scheduler and dispatcher are enabled, the highest priority, ready task will be dispatched to run. Control will not be returned to the Board Support Package after multitasking is enabled until the rtems_shutdown_executive directive is called. This directive is called as a side-effect of POSIX calls including exit.

RTEMS C User's Guide