The open Chiisai standard enables cross-vendor development of HALs, middleware, and embedded software for small microcontrollers. Bildrechte: Vector Informatik GmbH
Vector is releasing Chiisai, a fully open and royalty-free specification that fundamentally simplifies the development of hardware abstraction layers (HAL) on small microcontrollers. Chiisai aims to keep HAL implementations deliberately lean: the specification focuses on essential basic functions, thereby reducing the software footprint and supporting the efficient use of resource-constrained microcontrollers.
The name Chiisai, Japanese for “small”, reflects the specification’s focus on microcontrollers with limited resources, commonly used in sensors, actuators, and other compact embedded systems. The Chiisai specification defines standardized interfaces for relevant basic and communication functions and clearly separates drivers from middleware. This allows software components to be reused more easily across different hardware platforms.
Developed in collaboration with the semiconductor industry
Chiisai was developed in close collaboration with Infineon Technologies, the global market leader in microcontrollers (Omdia, 2025). Infineon Technologies contributed its extensive expertise in microcontrollers and hardware to the development of the Chiisai specification, helping to ensure that it was tailored specifically to small microcontrollers.
The goal is to standardize HAL development on small microcontrollers in a practical, efficient, and vendor-neutral manner. In addition to Infineon, other semiconductor manufacturers, such as Microchip Technology, are already actively supporting the Chiisai standard and are jointly driving the setup of an open, vendor-neutral software ecosystem.
An open standard for a growing software ecosystem
The Chiisai HAL specification provides an open standard that simplifies the development of vendor-independent HALs. The specification significantly lowers barriers to entry, enabling the rapid development of custom HALs and their use by a wide variety of middleware solutions, regardless of the microcontroller or hardware manufacturer. This creates a growing, cross-vendor ecosystem that promotes interoperability, reduces integration effort, and facilitates collaboration between OEMs, Tier-1 suppliers, and semiconductor manufacturers. As a result, companies across the entire value chain benefit from easier access to modern embedded and SDV-related software stacks.
Full compatibility with MICROSAR IO
The interfaces of Vector’s new software base-layer, MICROSAR IO, are fully compatible with the Chiisai specification. Once a Chiisai-compliant HAL is available for a microcontroller, MICROSAR IO can be deployed on that hardware platform without any additional customization effort. At the same time, MICROSAR IO is just one of many middleware solutions that can be built on top of a Chiisai-based HAL.
Availability: Chiisai is available under the following repository: https://github.com/vectorgrp/chiisai-hal-specification
More information about Chiisai on the Vector website: www.vector.com/en/industries/automotive/application-areas/chiisai-specification/