6. Initialization Manager¶

6.1. Introduction¶

The Initialization Manager is responsible for initializing the Board Support Package, RTEMS, device drivers, the root filesystem and the application. The Fatal Error Manager is responsible for the system shutdown.

The Initialization Manager provides only one directive:

rtems_initialize_executive - Initialize RTEMS

6.2. Background¶

6.2.1. Initialization Tasks¶

Initialization task(s) are the mechanism by which RTEMS transfers initial control to the user’s application. Initialization tasks differ from other application tasks in that they are defined in the User Initialization Tasks Table and automatically created and started by RTEMS as part of its initialization sequence. Since the initialization tasks are scheduled using the same algorithm as all other RTEMS tasks, they must be configured at a priority and mode which will ensure that they will complete execution before other application tasks execute. Although there is no upper limit on the number of initialization tasks, an application is required to define at least one.

A typical initialization task will create and start the static set of application tasks. It may also create any other objects used by the application. Initialization tasks which only perform initialization should delete themselves upon completion to free resources for other tasks. Initialization tasks may transform themselves into a “normal” application task. This transformation typically involves changing priority and execution mode. RTEMS does not automatically delete the initialization tasks.

6.2.2. The Idle Task¶

The Idle Task is the lowest priority task in a system and executes only when no other task is ready to execute. The default implementation of this task consists of an infinite loop. RTEMS allows the Idle Task body to be replaced by a CPU specific implementation, a BSP specific implementation or an application specific implementation.

The Idle Task is preemptible and WILL be preempted when any other task is made ready to execute. This characteristic is critical to the overall behavior of any application.

6.2.3. Initialization Manager Failure¶

System initialization errors are fatal. See Chapter 21 Section 2.3 - Internal Error Codes.

6.3. Operations¶

6.3.1. Initializing RTEMS¶

The Initialization Manager rtems_initialize_executive() directives is called by the boot_card() routine which is invoked by the Board Support Package once a basic C run-time environment is set up. This consists of

a valid and accessible text section, read-only data, read-write data and zero-initialized data,
an initialization stack large enough to initialize the rest of the Board Support Package, RTEMS and the device drivers,
all registers and components mandated by Application Binary Interface, and
disabled interrupts.

The rtems_initialize_executive() directive uses a system initialization linker set to initialize only those parts of the overall RTEMS feature set that is necessary for a particular application. Each RTEMS feature used the application may optionally register an initialization handler. The system initialization API is available via #included <rtems/sysinit.h>.

A list of all initialization steps follows. Some steps are optional depending on the requested feature set of the application. The initialization steps are execute in the order presented here.

RTEMS_SYSINIT_BSP_WORK_AREAS: The work areas consisting of C Program Heap and the RTEMS Workspace are initialized by the Board Support Package. This step is mandatory.
RTEMS_SYSINIT_BSP_START: Basic initialization step provided by the Board Support Package. This step is mandatory.
RTEMS_SYSINIT_CPU_COUNTER: Initialization of the CPU counter hardware and support functions. The CPU counter is initialized early to allow its use in the tracing and profiling of the system initialization sequence. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_INITIAL_EXTENSIONS: Registers the initial extensions. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_MP_EARLY: Early MPCI initialization. This step is mandatory on MPCI configurations.
RTEMS_SYSINIT_DATA_STRUCTURES: This directive is called when the Board Support Package has completed its basic initialization and allows RTEMS to initialize the application environment based upon the information in the Configuration Table, User Initialization Tasks Table, Device Driver Table, User Extension Table, Multiprocessor Configuration Table, and the Multiprocessor Communications Interface (MPCI) Table.
RTEMS_SYSINIT_MP: MPCI initialization. This step is mandatory on MPCI configurations.
RTEMS_SYSINIT_USER_EXTENSIONS: Initialization of the User Extensions object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_CLASSIC_TASKS: Initialization of the Classic Tasks object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_CLASSIC_TIMER: Initialization of the Classic Timer object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_CLASSIC_SIGNAL: Initialization of the Classic Signal support. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_CLASSIC_EVENT: Initialization of the Classic Event support. This step is optional and depends on the application configuration. This step is only used on MPCI configurations.
RTEMS_SYSINIT_CLASSIC_MESSAGE_QUEUE: Initialization of the Classic Message Queue object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_CLASSIC_SEMAPHORE: Initialization of the Classic Semaphore object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_CLASSIC_PARTITION: Initialization of the Classic Partition object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_CLASSIC_REGION: Initialization of the Classic Region object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_CLASSIC_DUAL_PORTED_MEMORY: Initialization of the Classic Dual-Ported Memory object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_CLASSIC_RATE_MONOTONIC: Initialization of the Classic Rate-Monotonic object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_CLASSIC_BARRIER: Initialization of the Classic Barrier object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_POSIX_SIGNALS: Initialization of the POSIX Signals support. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_POSIX_THREADS: Initialization of the POSIX Threads object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_POSIX_MESSAGE_QUEUE: Initialization of the POSIX Message Queue object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_POSIX_SEMAPHORE: Initialization of the POSIX Semaphore object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_POSIX_TIMER: Initialization of the POSIX Timer object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_POSIX_KEYS: Initialization of the POSIX Keys object class. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_POSIX_CLEANUP: Initialization of the POSIX Cleanup support. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_IDLE_THREADS: Initialization of idle threads. This step is mandatory.
RTEMS_SYSINIT_LIBIO: Initialization of IO library. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_ROOT_FILESYSTEM: Initialization of the root filesystem. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_DRVMGR: Driver manager initialization. This step is optional and depends on the application configuration. Only available if the driver manager is enabled.
RTEMS_SYSINIT_MP_SERVER: MPCI server initialization. This step is mandatory on MPCI configurations.
RTEMS_SYSINIT_BSP_PRE_DRIVERS: Initialization step performed right before device drivers are initialized. This step is mandatory.
RTEMS_SYSINIT_DRVMGR_LEVEL_1: Driver manager level 1 initialization. This step is optional and depends on the application configuration. Only available if the driver manager is enabled.
RTEMS_SYSINIT_DEVICE_DRIVERS: This step initializes all statically configured device drivers and performs all RTEMS initialization which requires device drivers to be initialized. This step is mandatory. In a multiprocessor configuration, this service will initialize the Multiprocessor Communications Interface (MPCI) and synchronize with the other nodes in the system.
RTEMS_SYSINIT_DRVMGR_LEVEL_2: Driver manager level 2 initialization. This step is optional and depends on the application configuration. Only available if the driver manager is enabled.
RTEMS_SYSINIT_DRVMGR_LEVEL_3: Driver manager level 3 initialization. This step is optional and depends on the application configuration. Only available if the driver manager is enabled.
RTEMS_SYSINIT_DRVMGR_LEVEL_4: Driver manager level 4 initialization. This step is optional and depends on the application configuration. Only available if the driver manager is enabled.
RTEMS_SYSINIT_MP_FINALIZE: Finalize MPCI initialization. This step is mandatory on MPCI configurations.
RTEMS_SYSINIT_CLASSIC_USER_TASKS: Creates and starts the Classic initialization tasks. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_POSIX_USER_THREADS: Creates POSIX initialization threads. This step is optional and depends on the application configuration.
RTEMS_SYSINIT_STD_FILE_DESCRIPTORS: Open the standard input, output and error file descriptors. This step is optional and depends on the application configuration.

The final action of the rtems_initialize_executive() directive is to start multitasking and switch to the highest priority ready thread. RTEMS does not return to the initialization context and the initialization stack may be re-used for interrupt processing.

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 Chapter 24 - Configuring a System.

6.3.2. Global Construction¶

The global construction is carried out by the first Classic API initialization task (first is defined by index zero in the Classic API initialization task configuration table). If no Classic API initialization task exists, then it is carried out by the first POSIX API initialization thread. If no initialization task or thread exists, then no global construction is performed, see for example Specify Idle Task Performs Application Initialization. The Classic API task or POSIX API thread which carries out global construction is called the main thread.

Global construction runs before the entry function of the main thread. The configuration of the main thread must take the global construction into account. In particular, the main thread stack size, priority, attributes and initial modes must be set accordingly. Thread-local objects and POSIX key values created during global construction are accessible by the main thread. If other initialization tasks are configured, and one of them has a higher priority than the main thread and the main thread is preemptible, this task executes before the global construction. In case the main thread blocks during global construction, then other tasks may run. In SMP configurations, other initialization tasks may run in parallel with global construction. Tasks created during global construction may preempt the main thread or run in parallel in SMP configurations. All RTEMS services allowed in task context are allowed during global construction.

Global constructors are C++ global object constructors or functions with the constructor attribute. For example, the following test program

#include <stdio.h>
#include <assert.h>

class A {
  public:
    A()
    {
      puts( "A:A()" );
    }
};

static A a;

static thread_local int i;

static thread_local int j;

static __attribute__(( __constructor__ )) void b( void )
{
  i = 1;
  puts( "b()" );
}

static __attribute__(( __constructor__( 1000 ) )) void c( void )
{
  puts( "c()" );
}

int main( void )
{
  assert( i == 1 );
  assert( j == 0 );
  return 0;
}

should output:

c()
b()
A:A()

6.4. Directives¶

This section details the Initialization Manager’s directives. A subsection is dedicated to each of this manager’s directives and describes the calling sequence, related constants, usage, and status codes.

6.4.1. INITIALIZE_EXECUTIVE - Initialize RTEMS¶

CALLING SEQUENCE:

void rtems_initialize_executive(void);

DIRECTIVE STATUS CODES:

NONE - This function will not return to the caller.

DESCRIPTION:

Iterates through the system initialization linker set and invokes the registered handlers. The final step is to start multitasking.

NOTES:

This directive should be called by boot_card() only.

This directive does not return to the caller. Errors in the initialization sequence are usually fatal and lead to a system termination.