This product is a real-time operating system (RTOS) conforming to the μITRON 4.0-specification, the predominant RTOS for embedded systems in Japan. Its compact resources, outstanding real-time features, and many service calls are suited for an embedded system with real-time ability and multi-tasking functions. In addition, its affinity for the IDE CS+ and the configurator which automatically generates startup files will help you greatly reduce development time and get to market faster.

This real-time operating system only supports the RL78, 78K family C compiler package. It does not support the RL78 family C compiler package.

  • TRON Forum holds the copyright on the μITRON Specification.
  • TRON, ITRON, and μITRON do not refer to any specific product or products.

Release Information


Latest Ver.: V1.00.02

Released: Nov 1, 2012

Details of upgrade (See Tool News)

Operating Environment

Agreement Details

 User's Manual( Coding | All )

CS+ interface plug-ins (RTOS Common plug-in)

Latest Ver.: V3.00.00

Released: Oct 1, 2014

CS+ interface plug-ins (Plug-in for RI600PX)

Latest Ver.: V3.00.00

Released: Oct 1, 2014

Cooperating Tools

  • Supported compiler :CC-RL
  • Supported IDE :CS+



  • Conforms to µITRON Ver. 4.0 Specification:
    The design conforms to the µITRON Ver. 4.0 Specification, the representative OS architecture for embedded control.
  • Excellent portability:
    In order to support many execution environments, the hardware-dependent processing necessary for the RI78V4 to execute processes has been extracted as target-dependent and user own coding portions and is provided as sample source files. In this way, portability to many different execution environments has been improved and customization is easy.
  • ROM-based implementation:
    Since the system is a real-time/multitask OS assumed to be used embedded in the execution environment, it was designed to be compact and ready for ROM-based implementations. Also, because the system can be configured linking only the service calls used in the application system by the user (rather than all the service calls provided by the RI78V4), a real-time/multitask OS can be configured which is compact and optimized for the user's needs.
  • Interface with CS+, the Renesas Electronics Integrated Development Environment
    The RI78V4 OS interfaces with CS+ to support the following functions:
    • Auto-settings for options required in OS build
    • Displays state of OS control object for tasks, semaphore, etc. (Resource Information)
    • Graphical displays of task operation history and service call issuance history (system performance analyzer)


The RI78V4 kernel consists of the following modules. Each module is provided by functions (service calls) .

  • Task management functions
    The task control functions provided by the RI78V4 include a function to reference task statuses, in addition to a function to manipulate task statuses.
  • Task dependent synchronization functions
    Changes task status from other task, and synchronizes tasks.
  • Synchronization and communication functions
    The synchronization and communication functions of the RI78V4 consist of Semaphores, Eventflags, and Mailboxes that are provided as means for realizing exclusive control, queuing, and communication among tasks.
    • Semaphores: In the RI78V4, non-negative number counting semaphores are provided as a means (exclusive control function) for preventing contention for limited resources (hardware devices, library function, etc.) arising from the required conditions of simultaneously running tasks.
    • Eventflags: Provides 16-bit eventflags as a queuing function for tasks, such as keeping the tasks waiting for execution, until the results of the execution of a given processing program are output.
    • Mailboxes: Provides a mailbox, as a communication function between tasks, that hands over the execution result of a given processing program to another processing program.

  • Fixed-sized memory pool
    When a dynamic memory manipulation request is issued from a processing program in the RI78V4, the fixed-sized memory pool is provided as a usable memory area.
  • Time management functions
    The time management functions of the RI78V4 include Delayed Wakeup, Timeout, and Cyclic Handlers that use timer interrupts created as fixed intervals, as means for realizing time-dependent processing.
  • System state management functions
    For changing or referencing the system state.
  • Interrupt management functions
    Provides as interrupt management functions related to the interrupt handlers activated when a maskable interrupt is occurred.
  • System configuration management functions
    Provides system initialization processing, which is required from the reset interrupt output until control is passed to the task, and version information referencing processing.
  • Scheduler
    The scheduling functions provided by the RI78V4 consist of functions manage/decide the order in which tasks are executed by monitoring the transition states of dynamically changing tasks, so that the CPU use right is given to the optimum task.



Target device RL78 Family, 78K0R
Maximum number of tasks 127
Number of priority levels 15
Service call number 66
(Time takes for a target task to be executed after the wup_tas is issued.)
49.2 microseconds
(78K0R/Kx3, 10MHz. embedded memory)
Kernel code size From 2.9K bytes to 7.7K bytes
Kernel RAM usage per task data : 24 bytes
stack : 28 bytes


Provided items Explanation Note
Kernel source program Kernel source program Provided only with mass- production licenses which include source code.
Kernel library Kernel library for system building -
Standard header files ITRON specification common definition files
Kernel specification definition files
Other definition files
Header files are provided both in C languages
Command line configurator Outputs all types of definition files from the cfg file that describes the structure parameters in text. -
Sample program A simple program using ITRON. -
CS+ interface plug-ins
- RTOS Common plug-in
- Plug-in for RI78V4
Function for easy kernel embedding
Function for referencing the OS state during debug
System performance analyzer A tool that displays a transition diagram of the OS operation history and analyzes performance, such as CPU usage rate. -
Manual User's manual -

Processing Flow

Devices with exceedingly low ROM or RAM capacity are not supported even if the groups they belong to are listed on the above list of supported devices. The standard capacities of ROM and RAM are stated below. Note that the required capacities also depend on the applications you will be using.

  • ROM capacity: At least 16 KB
  • RAM capacity: At least 4 KB

Information supporting development tools

Title Description
My Renesas Create a My Renesas account to use our tool download services,
receive e-newsletter/update notifications, and take advantage of our other services.
e-learning Information for studying and learning about microcontrollers and microprocessors.
FAQ Frequently asked questions and useful hints for development.
Forum A forum and community site to share technical information,
questions and opinions with others who use Renesas MCU's.
Tool News Tool release information and other important information.
Operating Environment Information on system requirements and operating environment for the latest
version of tools.
Info on Discontinued Products A list of Renesas software and tools that have been discontinued and
are no longer being offered for new projects.