RTEMS 4.0.0 On-Line Library

Configuring a System Configuration Table

RTEMS C User's Guide

21.1: Configuration Table

The RTEMS Configuration Table is used to tailor an application for its specific needs. For example, the user can configure the number of device drivers or which APIs may be used. THe address of the user-defined Configuration Table is passed as an argument to the rtems_initialize_executive directive, which MUST be the first RTEMS directive called. The RTEMS Configuration Table is defined in the following C structure:

typedef struct {
  void                             *work_space_start;
  rtems_unsigned32                  work_space_size;
  rtems_unsigned32                  maximum_extensions;
  rtems_unsigned32                  microseconds_per_tick;
  rtems_unsigned32                  ticks_per_timeslice;
  rtems_unsigned32                  maximum_devices;
  rtems_unsigned32                  number_of_device_drivers;
  rtems_driver_address_table       *Device_driver_table;
  rtems_unsigned32                  number_of_initial_extensions;
  rtems_extensions_table           *User_extension_table;
  rtems_multiprocessing_table      *User_multiprocessing_table;
  rtems_api_configuration_table    *RTEMS_api_configuration;
  posix_api_configuration_table    *POSIX_api_configuration;
} rtems_configuration_table;

work_space_start: is the address of the RTEMS RAM Workspace. This area contains items such as the various object control blocks (TCBs, QCBs, ...) and task stacks. If the address is not aligned on a four-word boundary, then RTEMS will invoke the fatal error handler during rtems_initialize_executive.
work_space_size: is the calculated size of the RTEMS RAM Workspace. The section Sizing the RTEMS RAM Workspace details how to arrive at this number.
microseconds_per_tick: is number of microseconds per clock tick.
ticks_per_timeslice: is the number of clock ticks for a timeslice.
maximum_devices: is the maximum number of devices that can be registered.
number_of_device_drivers: is the number of device drivers for the system. There should be the same number of entries in the Device Driver Table. If this field is zero, then the User_driver_address_table entry should be NULL.
Device_driver_table: is the address of the Device Driver Table. This table contains the entry points for each device driver. If the number_of_device_drivers field is zero, then this entry should be NULL. The format of this table will be discussed below.
number_of_initial_extensions: is the number of initial user extensions. There should be the same number of entries as in the User_extension_table. If this field is zero, then the User_driver_address_table entry should be NULL.
User_extension_table: is the address of the User Extension Table. This table contains the entry points for the static set of optional user extensions. If no user extensions are configured, then this entry should be NULL. The format of this table will be discussed below.
User_multiprocessing_table: is the address of the Multiprocessor Configuration Table. This table contains information needed by RTEMS only when used in a multiprocessor configuration. This field must be NULL when RTEMS is used in a single processor configuration.
RTEMS_api_configuration: is the address of the RTEMS API Configuration Table. This table contains information needed by the RTEMS API. This field should be NULL if the RTEMS API is not used. [NOTE: Currently the RTEMS API is required to support support components such as BSPs and libraries which use this API.]
POSIX_api_configuration: is the address of the POSIX API Configuration Table. This table contains information needed by the POSIX API. This field should be NULL if the POSIX API is not used.

RTEMS C User's Guide