no-OS license rules

no-OS is, by default, permissively licensed under BSD-3-Clause. Individual files may be under different terms, always stated in the file's own header. This page explains how licenses are declared and organized so that the license of any file is clear and, where possible, machine readable.

The top-level COPYING file is a short pointer to this default and to this page. The license of any individual file is stated by its own SPDX tag or header; that tag is authoritative.

Declaring a license in a source file

Every source file should declare its license with an SPDX identifier in its header comment, in a form appropriate to the file type (some older files, mostly build files and scripts, are still being converted). For C sources and headers:

/* SPDX-License-Identifier: BSD-3-Clause */

For scripts and other #-comment files:

# SPDX-License-Identifier: BSD-3-Clause

The SPDX tag is authoritative for that file, and is required for new no-OS code because it is precise and machine parsable. Analog Devices' own no-OS sources carry this tag (usually alongside a copyright line) rather than the full BSD boilerplate.

The `LICENSES/` directory

The full text of every license used by Analog Devices' own no-OS code is collected under LICENSES/, one file per license, grouped by role:

LICENSES/preferred/

BSD-3-Clause (the default and the only license for new no-OS code).

LICENSES/permissive/

Permissive licenses that are allowed but are not the default:

Apache-2.0 — the ADRV903x (palma) and ADRV904x (koror) vendor APIs, the generated firmware/profile files of the adrv903x and adrv904x projects, and the Maxim SDK lwIP port header libraries/lwip-glue/arch/cc.h.
MIT — third-party code kept under its original license, e.g. the Xilinx-derived drivers/platform/xilinx/xilinx_uart.c, the LVGL lv_conf.h files, the jsmn parser in the navassa tree, the Azure IoT sample code in eval-ade9430 and the ad5293 driver.
OFL-1.1 — font data generated from OFL-licensed fonts.

LICENSES/proprietary/

Non-permissive ADI vendor device-API licenses, each confined to its driver subtree and the matching example project (detailed below): LicenseRef-ADI-API-License, LicenseRef-ADI-ADRV9025-SLA, LicenseRef-ADI-ADRV9001-SLA, LicenseRef-ADI-AD9084-SLA and LicenseRef-ADI-AD937X-Firmware-CTSLA.

Each license file begins with a Valid-License-Identifier: line (the SPDX or repository-local LicenseRef- identifier), an optional SPDX-URL: for standard licenses, a Usage-Guide: describing when the license may be used, and the full License-Text:.

Repository-local `LicenseRef-` identifiers

Some licenses used by no-OS are not standard SPDX licenses, so they use REUSE-style repository-local identifiers:

LicenseRef-ADI-API-License — the ADI "Source Code Software License Agreement" 20130524-CISC-CTSLA carried by the talise, ad9083, ad9208 and ad917x vendor API files and the ad9371 and adrv9009 project trees.
LicenseRef-ADI-ADRV9025-SLA — the ADI "Software License Agreement" 20180813-ADI-N3PT-CTSLA carried by the ADRV9025 (madura) vendor API files and the generated profiles and platform glue of the adrv902x project; the same non-permissive ADI "API license" family. It expressly forbids subjecting the software to source-disclosure terms.
LicenseRef-ADI-AD937X-Firmware-CTSLA — the ADI "Software License Agreement" 20180301-AD937X-CTSLA carried by the Talise (AD937x) ARM and stream firmware binaries under drivers/rf-transceiver/talise/firmware and the AD9371 (Mykonos) firmware header in the ad9371 project; the same non-permissive ADI "API license" family. It covers firmware object code and expressly forbids subjecting the software to any "Excluded License" (source-disclosure terms).
LicenseRef-ADI-ADRV9001-SLA — the ADI "Software License Agreement" 20190814-APIGUIHDLFWNAV-CTSLA carried by the ADRV9001 SDK (navassa) vendor API files under drivers/rf-transceiver/navassa and the generated profiles of the adrv9001 project; the same non-permissive ADI "API license" family.
LicenseRef-ADI-AD9084-SLA — the ADI "Software License Agreement" 2026-05-25-AD9084-SDK-2.1.0-GA-SLA carried by the AD9084/AD9088 SDK (Apollo) vendor API files and firmware images under drivers/rf-transceiver/ad9088; the same non-permissive ADI "API license" family. It incorporates by reference the terms published at https://www.analog.com/en/support/software-license-agreement.html.

They are non-permissive and must not be used for new files.

Acceptable licenses for new contributions

New contributions must use the permissive BSD-3-Clause license. See the "Licensing of contributions" section of Contributing to no-OS for the full rule, including the exceptions for vendor-supplied device APIs that cannot be relicensed and for third-party code kept under its original permissive license.

Third-party libraries

Third-party libraries are not stored in the repository. They are fetched at configure time (pinned via Kconfig) into libraries/<repo-name>/, and each carries its own LICENSE / COPYING file, which governs that library; they are not re-described under LICENSES/. A library is only fetched and built when a project selects it.

Library	License
`libraries/FreeRTOS-Kernel/`	`MIT`
`libraries/azure-sdk-for-c/`	`MIT`
`libraries/lvgl/`	`MIT`
`libraries/TMC-API/`	`MIT`
`libraries/mbedtls/`	`Apache-2.0`
`libraries/esh/`	`Apache-2.0`
`libraries/precision-converters-library/`	`Apache-2.0`
`libraries/lwip/`	`BSD-3-Clause`
`libraries/pico-sdk/`	`BSD-3-Clause`
`libraries/paho.mqtt.embedded-c/`	`EPL-1.0` / `EDL-1.0`
`libraries/ftd2xx/`	FTDI D2XX driver license (proprietary, downloaded from FTDI)

Two kinds of code are tracked under libraries/:

libraries/fatfs/ is a bundled copy of FatFs, under the FatFs license (BSD-like) in libraries/fatfs/LICENSE.txt.
The no-OS glue code for the fetched libraries — libraries/esh-glue/, libraries/lwip-glue/, libraries/mqtt/ and libraries/fatfs/adi_diskio.c. Each file carries its own SPDX tag or license header; lwip-glue/configs/ holds lwIP configuration headers under lwIP's BSD-3-Clause license.