Introduction to the TOPPERS Project - Open Source RTOS for Embedded Systems

The TOPPERS Project is to develop a series of open source real-time operating systems (RTOS) for embedded systems. The TOPPERS/JSP Kernel, which is the first product of the project, was released two years ago and is started to be used in industries. A technological basis of the TOPPERS Project is the ITRON Specification, which is a de-facto standard real-time kernel specification widely applied to consumer electronics, cellular phones, and other small-scale embedded systems in Japan. 1 ITRON Specifications ITRON is a series of specifications for real-time operating systems (RTOS) and related standards for embedded systems [1, 2]. The standardization of the ITRON Specifications is being conducted as one of the sub-projects of the TRON Project and was started in 1984. The ITRON Specifications are open in that anyone can freely implement software based on the specifications. Until now, four generations of the ITRON real-time kernel specifications have been developed and published. The latest version of the specifications is the μITRON4.0 Specification, which was released in 1999 [3]. The letter “μ” shows that its main target is small-scale embedded systems. The ITRON Specifications have been implemented for a number of processors and widely applied to various kind of embedded systems, especially to small-scale embedded systems such as consumer electronics and cellular phones. According to a questionnaire-based survey conducted by the TRON Association, real-time kernels conforming to the ITRON Specifications are adopted in about one third of the embedded system designs recently developed in Japan [7]. Some other standards related to the kernel specification, such as the ITRON TCP/IP API Specification [4], the JTRON (Java on ITRON) Specification [5], and the ITRON Debugging Interface Specification [6], have been also developed. Though the ITRON Specifications are successful as standard specifications, some problems caused by a lack of standard implementation are pointed out. For example, the detailed specifications and the inner structures of the real-time kernels based on the ITRON Specifications are different each other because of the implementation-dependent matters included in the standard specifications. This problem of excessive diversity makes the reuse of software components and development tools to other ITRON-specification kernels difficult.