4. RTEMS Data Types — RTEMS Classic API Guide 5.4-rc2 (21st August 2026) documentation

# 4. RTEMS Data Types

## 4.1. Introduction

This chapter contains a complete list of the RTEMS primitive data types in alphabetical order. This is intended to be an overview and the user is encouraged to look at the appropriate chapters in the manual for more information about the usage of the various data types.

## 4.2. List of Data Types

The following is a complete list of the RTEMS primitive data types in alphabetical order:

`rtems_address`

  The data type used to manage addresses. It is equivalent to a `void *` pointer.

`rtems_asr`

  The return type for an RTEMS ASR.

`rtems_asr_entry`

  The address of the entry point to an RTEMS ASR.

`rtems_attribute`

  The data type used to manage the attributes for RTEMS objects. It is primarily used as an argument to object create routines to specify characteristics of the new object.

`rtems_boolean`

  This type is deprecated will be removed in RTEMS 6.1. Use `bool` instead.

`rtems_context`

  This type is deprecated will be removed in RTEMS 6.1.

`rtems_context_fp`

  This type is deprecated will be removed in RTEMS 6.1.

`rtems_device_driver`

  The return type for a RTEMS device driver routine.

`rtems_device_driver_entry`

  The entry point to a RTEMS device driver routine.

`rtems_device_major_number`

  The data type used to manage device major numbers.

`rtems_device_minor_number`

  The data type used to manage device minor numbers.

`rtems_double`

  This type is deprecated will be removed in RTEMS 6.1. Use `double` instead.

`rtems_event_set`

  The data type used to manage and manipulate RTEMS event sets with the Event Manager.

`rtems_extension`

  The return type for RTEMS user extension routines.

`rtems_fatal_extension`

  The entry point for a fatal error user extension handler routine.

`rtems_id`

  The data type used to manage and manipulate RTEMS object IDs.

`rtems_interrupt_frame`

  The data structure that defines the format of the interrupt stack frame as it appears to a user ISR. This data structure is only defined on architectures that pass the frame pointer to the ISR handler.

`rtems_interrupt_level`

  The data structure used with the `rtems_interrupt_disable`, `rtems_interrupt_enable`, and `rtems_interrupt_flash` routines. This data type is CPU dependent and usually corresponds to the contents of the processor register containing the interrupt mask level.

`rtems_interval`

  The data type used to manage and manipulate time intervals. Intervals are non-negative integers used to measure the length of time in clock ticks.

`rtems_isr`

  The return type of a function implementing an RTEMS ISR.

`rtems_isr_entry`

  The address of the entry point to an RTEMS ISR. It is equivalent to the entry point of the function implementing the ISR.

`rtems_mp_packet_classes`

  The enumerated type which specifies the categories of multiprocessing messages. For example, one of the classes is for messages that must be processed by the Task Manager.

`rtems_mode`

  The data type used to manage and dynamically manipulate the execution mode of an RTEMS task.

`rtems_mpci_entry`

  The return type of an RTEMS MPCI routine.

`rtems_mpci_get_packet_entry`

  The address of the entry point to the get packet routine for an MPCI implementation.

`rtems_mpci_initialization_entry`

  The address of the entry point to the initialization routine for an MPCI implementation.

`rtems_mpci_receive_packet_entry`

  The address of the entry point to the receive packet routine for an MPCI implementation.

`rtems_mpci_return_packet_entry`

  The address of the entry point to the return packet routine for an MPCI implementation.

`rtems_mpci_send_packet_entry`

  The address of the entry point to the send packet routine for an MPCI implementation.

`rtems_mpci_table`

  The data structure containing the configuration information for an MPCI.

`rtems_name`

  The data type used to contain the name of a Classic API object. It is an unsigned thirty-two bit integer which can be treated as a numeric value or initialized using `rtems_build_name` to contain four ASCII characters.

`rtems_option`

  The data type used to specify which behavioral options the caller desires. It is commonly used with potentially blocking directives to specify whether the caller is willing to block or return immediately with an error indicating that the resource was not available.

`rtems_packet_prefix`

  The data structure that defines the first bytes in every packet sent between nodes in an RTEMS multiprocessor system. It contains routing information that is expected to be used by the MPCI layer.

`rtems_signal_set`

  The data type used to manage and manipulate RTEMS signal sets with the Signal Manager.

`int8_t`

  The C99 data type that corresponds to signed eight bit integers. This data type is defined by RTEMS in a manner that ensures it is portable across different target processors.

`int16_t`

  The C99 data type that corresponds to signed sixteen bit integers. This data type is defined by RTEMS in a manner that ensures it is portable across different target processors.

`int32_t`

  The C99 data type that corresponds to signed thirty-two bit integers. This data type is defined by RTEMS in a manner that ensures it is portable across different target processors.

`int64_t`

  The C99 data type that corresponds to signed sixty-four bit integers. This data type is defined by RTEMS in a manner that ensures it is portable across different target processors.

`rtems_single`

  This type is deprecated will be removed in RTEMS 6.1. Use `float` instead.

`rtems_status_code`

  The return type for most RTEMS services. This is an enumerated type of approximately twenty-five values. In general, when a service returns a particular status code, it indicates that a very specific error condition has occurred.

`rtems_task`

  The return type for an RTEMS Task.

`rtems_task_argument`

  The data type for the argument passed to each RTEMS task. In RTEMS 4.7 and older, this is an unsigned thirty-two bit integer. In RTEMS 4.8 and newer, this is based upon the C99 type `uintptr_t` which is guaranteed to be an integer large enough to hold a pointer on the target architecture.

`rtems_task_begin_extension`

  The entry point for a task beginning execution user extension handler routine.

`rtems_task_create_extension`

  The entry point for a task creation execution user extension handler routine.

`rtems_task_delete_extension`

  The entry point for a task deletion user extension handler routine.

`rtems_task_entry`

  The address of the entry point to an RTEMS ASR. It is equivalent to the entry point of the function implementing the ASR.

`rtems_task_exitted_extension`

  The entry point for a task exitted user extension handler routine.

`rtems_task_priority`

  The data type used to manage and manipulate task priorities.

`rtems_task_restart_extension`

  The entry point for a task restart user extension handler routine.

`rtems_task_start_extension`

  The entry point for a task start user extension handler routine.

`rtems_task_switch_extension`

  The entry point for a task context switch user extension handler routine.

`rtems_tcb`

  The data structure associated with each task in an RTEMS system.

`rtems_time_of_day`

  The data structure used to manage and manipulate calendar time in RTEMS.

`rtems_timer_service_routine`

  The return type for an RTEMS Timer Service Routine.

`rtems_timer_service_routine_entry`

  The address of the entry point to an RTEMS TSR. It is equivalent to the entry point of the function implementing the TSR.

`rtems_vector_number`

  The data type used to manage and manipulate interrupt vector numbers.

`uint8_t`

  The C99 data type that corresponds to unsigned eight bit integers. This data type is defined by RTEMS in a manner that ensures it is portable across different target processors.

`uint16_t`

  The C99 data type that corresponds to unsigned sixteen bit integers. This data type is defined by RTEMS in a manner that ensures it is portable across different target processors.

`uint32_t`

  The C99 data type that corresponds to unsigned thirty-two bit integers. This data type is defined by RTEMS in a manner that ensures it is portable across different target processors.

`uint64_t`

  The C99 data type that corresponds to unsigned sixty-four bit integers. This data type is defined by RTEMS in a manner that ensures it is portable across different target processors.

`uintptr_t`

  The C99 data type that corresponds to the unsigned integer type that is of sufficient size to represent addresses as unsigned integers. This data type is defined by RTEMS in a manner that ensures it is portable across different target processors.