This product is a real-time operating system (real-time OS) that is an implementation of the μITRON4.0 specification. μITRON is the predominant real-time OS for embedded systems in Japan. Its low resource requirements, outstanding real-time performance, and broad range of service calls make it very suitable for embedded systems requiring true real-time and multi-tasking capabilities.

In addition, its high degree of compatibility with the CS+ IDE and the configurator which automatically generates startup files will help you greatly reduce development times and get your products to market more quickly.

This product is also available in the free trial version.


  • Conforms to µITRON4.0 Specification
    The design conforms to the µITRON4.0 Specification, the representative OS architecture for embedded control.
  • Achieving higher performance
    The times for processing service calls and the longest times over which interrupts must be disabled are shorter than for the RI78V4 V1. [Learn More]
  • 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/multi-tasking 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 system by the user (rather than all the service calls provided by the RI78V4), a real-time/multi-tasking OS can be configured which is compact and optimized for the user's needs.
  • Interface with CS+, the Renesas Electronics IDE
    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)
  • Supported compiler: CC-RL (the RL78 family C compiler package)
  • Learn More

Release Information


Latest Ver.: V2.00.00
Released: Jun 1, 2015
Details of upgrade (See Tool News)
Operating Environment
Agreement Details
User's Manual ( Coding: RI78V4 V2.00.00 Real-Time Operating System User's Manual: Coding (PDF | English, 日本語) | All )

CS+ interface plug-ins (Real-time OS Common plug-in)

Latest Ver.: V3.03.00
Released: Jul 1, 2016

CS+ interface plug-ins (Plug-in for RI78V4 V2)

Latest Ver.: V2.01.00
Released: Jul 1, 2016

Target Devices

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


Design & Development

Sample Code

Additional Details

Cooperating Tools

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


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, Data Queues, 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.
    • Data Queues: Provides the data queues that have the data queue area in which data read/write is enabled for transferring the prescribed size of data.
    • 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
Maximum number of tasks 127
Number of priority levels 15
Number of Service calls 76
Performance (Time takes for a target task to be executed after the wup_tsk is issued.) 11.80 microseconds
(RL78/G13, 10MHz. non-trace mode)
Kernel code size From 3.0K bytes to 9.0K bytes
Kernel RAM usage per task data : 24 bytes
stack : 20 bytes + amount being used by the user


Provided items Explanation Note
Kernel source program Source files for the kernel 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 in C language.
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
  • Real-time OS Common plug-in
  • Plug-in for RI78V4
  • Function for easy kernel embedding
  • Function for referencing the OS state during debug
  • 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



About Trial

We provide a trial software of the RI78V4 so that you can try out the functions and performance of RI78V4 before purchasing it. No support, including responses to inquiries through contact points, is provided for the trial software. Please accept this before using the trial software. In addition, please read through the Software User License Agreement ITRON (PDF | English, 日本語) and following notes before downloading.

Before Downloading

Cautionary Notes
  1. Difference with the Product Version
    Although the performance and functionality are the same as the product version, RI78V4 real-time OS of the trial software has the restrictions described below.
    • The RI78V4 OS stops working after 30 minutes (the program enters an infinite loop).
  2. Using the OS for Finished Products
    If you intend to embed the RI78V4 real-time OS in a finished product, use the product version. We do not offer any technical support services in case of troubles.
  3. Prohibition of Redistribution
    Redistribution of the software tool to third parties is strictly prohibited.
Operating Environment

The operating environment is same as the product version. Refer to Operating Environments of Products.


Please refer to RI78V4 Real-time OS for RL78 Family (Supported by CS+) Trial Software Further note Rev.1.00 (PDF | English, 日本語)