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Mbed OS 15.11 Technology Preview

This is the first public Technology Preview of Mbed OS and associated tools. We’re actively working on Mbed OS and we expect to make exciting changes in the next six months. We’re making this technology preview available so you can see the trajectory we’re on. Our focus in this release is on laying the foundation for Mbed OS development and collaboration, particularly core tools, technology and testing.

We expect Mbed OS developers to be able to access, build and run example projects and to explore the underlying code.

If you’re already using earlier versions of mbed, please note that Mbed OS is a new operating system; although it shares some code with Mbed Classic, it has its own structure, tools, APIs and philosophy. We recommend reading the links below to understand how Mbed OS differs from Mbed Classic and what you need to do to take full advantage of Mbed OS.

About this release

Note that this is a technology preview release, offering you early access to key features and innovations enabling you to test functionality. This release is not yet suitable for volume production use. The software is still maturing, and a number of things will change, including module names, repository URLs, APIs, header file names and configuration parameters. We'll try to mitigate the impact that these changes have on your code where possible, but please expect backwards-incompatible changes.

Note that in this release we're changing our version numbering scheme for Mbed OS releases, to a calendar-based (year and month YY.MM) scheme. This release (15.11) has previously been called 3.0 in some communications.


We're building Mbed OS as a collaborative project, bringing together industry and open source community contributions. If you’d like to work on Mbed OS with us, we’d encourage you to pitch in. With this technology preview we’re ready to start receiving contributions back from the community.


To get started with Mbed OS, please visit our getting started guides, which describe the tools you need to use Mbed OS, how to build and run your first Mbed OS program and where to find a few more examples.

To find out more about how Mbed OS is structured and the services currently available in mbed OS, please visit the Mbed OS repository on GitHub. It contains a list of the code repositories used in Mbed OS, a list of the currently supported targets and other useful information.

Feature Readiness

The following features are currently experimental:


  • The Mbed mesh networking stack includes an implementation of the Thread 1.0 specification that is considered experimental. Arm intends to provide full production support for Thread following completion of the Thread standard.


  • The mbed-mesh-api, which allows using 6LoWPAN mesh networks, currently uses static configuration. It does not provide an API for selecting the node operating mode, security option, radio channel or other options that are needed for connecting to 6LoWPAN networks. Configuration support will be available in later releases.

Mbed TLS

  • Support for EC J-PAKE is experimental and the Thread specification which requires it is itself not yet final.
  • Random number generation is not yet suitable for use in production.


  • Various APIs (including the asynchronous ones) are a work in progress; their signatures are expected to evolve over the next few releases.


  • The Mbed HAL APIs are subject to change. The current HAL APIs are an evolution of the blocking APIs from Mbed Classic, and have a number of limitations. In particular, the current APIs lack robust error handling (a requirement for production use), as well as consistent use of clock and power management and DMA and  documented implementation criteria and acceptance tests. We have big plans for the HAL. As with all other parts of the OS, we will signal incompatible changes to the HAL through the use of semantic versioning.


  • This version of the uVisor is an early tech preview, which has partial implementation of the security features that will be present in future versions. Please use this release for ensuring compatibility with uVisor (interrupt handling, memory protection model etc) but do not rely on it for security.

If you have any questions or comments about the readiness of features, please post in the Mbed forum.

Target Availability

Currently the only target device officially supported by the Arm Mbed team is the NXP FRDM-K64F board (yotta targets: `frdm-k64f-gcc` and `frdm-k64f-armcc`).

The following targets have experimental support:

  • NXP JN5179.
  • ST Nucleo F401 and DISCO-F4291.
  • Nordic - nRF51 DK and nRF51822-mKIT.
  • BBC micro:bit.
  • SiLabs EFM32 Giant Gecko and EFM32 Happy Gecko.

This document will be updated shortly with instructions on how to use Mbed OS on these targets.

Changes since the last release

This section documents the changes between this release and the earlier Mbed OS Beta (15.09) release.

Core libraries

  • core-util: FunctionPointer and Event are now in core-util.
  • minar:
    • Fixed a bug that forced some callbacks to be scheduled in the past.
    • Removed dependency on mbed-drivers.
  • ualloc: All headers are now in the ualloc header (mbed-alloc folder deprecated).


  • Event and FunctionPointer moved to core-util module.
  • mbed_sdk_init renamed to hal_init.
  • In SPI, we replaced the asynchronous API with a Fluent API (to allow easier selection of optional parameters).
  • All headers are now in mbed-drivers folder (Mbed folder deprecated).


  • mbed-hal:
    • Pin maps can now be specified using yotta config.
    • Serial: The bit width of the transfer word is now deprecated and will be removed in the future.
  • STM32:
    • Fixed prescaler computation for LPTMR.
    • HSE config can now be specified through yotta config.
    • Asynchronous SPI implementation.


6LoWPAN/Thread stack
  • UDP socket connect, send, close and bind functionality changed to match Mbed OS C++ Socket API.
  • Interoperability improvements against Thread 1.0 specification.
  • 6LoWPAN stack documentation published to
  • Added configuration for different operating modes.
  • Various bug fixes.
Networking Libraries
  • sal
    • Switched to dependency based on yotta config.
    • Added get_options and set_options to the API.
    • Moved include files to sal/.
  • sal-stack-lwip: Moved include files to sal-stack-lwip.
  • sockets: Moved include files to sockets.



The full yotta changelog can be found at This release requires yotta 0.9.1 or greater.

Test tools
  • greentea:
    • Added better support to latest yotta versions.
    • Changed application workflow to support one Mbed target test execution for every specified target.
    • Added support for pylint scans.
  • htrun:
    • Small improvements to OS support and documentation.
    • Added command line switch -b to send break command to devices.
    • Added support for pylint scans.
  • mbed-ls:
    • Added --mock command line switch; useful when prototyping and detecting new targets.
    • Fixed issue related to target detection on Ubuntu and Mac OS X.
    • Added support for pylint scans.

The main feature of this release is support for STM32F4 Arm Cortex-M4 devices using the Arm architected memory protection unit (MPU). In this release we support the two following target platforms for µVisor:

  • NXP FRDM-K64F (GCC Arm Embedded toolchain).
  • STMicroelectronics STM32F429I-DISCO (GCC Arm Embedded toolchain).

The previous beta release (15.09) demonstrated the creation of a sandbox that allocates private memories and requests individual access to security critical system peripherals using access control lists (ACLs) and demonstrating unprivileged interrupts. In this release we updated our example code with MINAR eventing.

We also added secure box contexts to provide efficient box-specific secure memories. These can be used for storing box-specific class instances, or other security-critical data that needs to be restricted to individual boxes.

To demonstrate µVisor we created a simple exploit demo: when pressing a switch on the development board, the main Mbed box attempts to read a secured password. The µVisor will intercept that attempt and deny access by halting the code (five red blinks). The error handling will be improved in future releases by supporting configurable debug channels.

More up-to-date information about the µVisor component can be found in our µVisor GitHub repository and our known issues list.

Mbed TLS

This release is based on Mbed TLS 2.2.0, while the Mbed OS Beta (15.09) release was based on Mbed TLS 2.1.0. Major changes between those versions include:

  • A new integrated C++ class library for TLS connections (currently only TLS clients) in the companion module mbed-tls-sockets.
  • Experimental support for the EC J-PAKE key exchange as defined in the Thread 1.0.0 draft specification. This support is disabled by default as the specification is not stable yet. See the Readme for instructions to enable it.
  • Fixes for security issues, including CVE-2015-5291.
  • Various bug fixes and improvements.

More details can be found in the ChangeLog.

Currently the only officially supported target platform for Mbed TLS in Mbed OS is the NXP FRDM-K64F board (yotta targets: `frdm-k64f-gcc` and `frdm-k64f-armcc`). We do not recommend using this release of Mbed TLS in production, because the port for the NXP FRDM-K64F board does not yet provide an adequate source of random numbers necessary for the cryptographic functions.

Bluetooth Low Energy

This release reintroduces the Mbed Classic Bluetooth Low Energy (BLE) APIs into Mbed OS. These APIs abstract vendors’ BLE implementations, including single-chip and external peripheral configurations. Currently there is reference support for targets based on Nordic's nRF51 family of MCUs, as well as experimental support for ST BLE shields on other target boards.

The Bluetooth API is hosted on GitHub. It comes with reference implementations for some Bluetooth-SIG specified GATT profiles and services; documented example applications can be found at

Mbed Client API

This release contains the following new features:

  • Securely connect to Mbed Device Server over TCP connection through TLS. The supported secure connection includes Certificate mode. We still support non-secure connection mode for fast development and debugging.
  • New LWM2M Firmware Object class preview for application development.

Known issues

The known issues for this release are described on GitHub.

Other ways of accessing this release

We prefer that you access and collaborate with Mbed OS online. However, the release may also be downloaded as a tar archive file. For further information, please start with the readme in the root directory of the archive.

Module versions in this release

We use semantic versioning for the modules in Mbed OS. This means that you can tell from the version number of a module what’s changed: an increase in the major version indicates a backwards incompatible change, and the minor and patch versions are used for backwards compatible features and bug-fixes respectively. When you use yotta to build an application that depends on a module, you can specify which sort of updates you will allow updates to. For more information on how yotta uses version specifications, see the yotta documentation.

This release comprises the following yotta modules and their versions:

Module Version
atmel-rf-driver 1.0.1
ble 2.0.3
BLE_URIBeacon 0.0.1
BLE_Thermomether 0.0.1
BLE_HeartRate 0.0.1
BLE_EddystoneObserver 0.0.1
BLE_EddystoneBeacon 0.0.1
BLE_Beacon 0.0.1
ble-nrf51822 2.0.2
cmsis-core 1.0.1
cmsis-core-freescale 1.0.0
cmsis-core-k64f 1.0.0
cmsis-core-nordic 1.0.1
cmsis-core-nrf51822 1.0.1
cmsis-core-st 1.0.0
cmsis-core-stm32f4 1.0.2
cmsis-core-stm32f429xi 1.0.2
compiler-polyfill 1.1.1
core-util 1.0.1
dlmalloc 1.0.0
example-asynch-i2c 1.0.1
example-asynch-serial 1.0.0
example-asynch-spi 1.0.1
example-mbedos-blinky 1.0.0
helloyotta 0.0.0
mbed-6lowpan-eventloop-adaptor 1.0.2
mbed-client 1.2.1
mbed-client-c 1.1.1
mbed-client-example-6lowpan 0.0.2
mbed-client-examples 1.1.0
mbed-client-libservice 3.0.8
mbed-client-mbed-os 1.1.0
mbed-client-mbed-tls 1.0.9
mbed-client-randlib 1.0.0
mbed-drivers 0.11.1
mbed-example-network 1.0.1
mbed-hal 1.0.5
mbed-hal-frdm-k64f 1.0.0
mbed-hal-freescale 1.0.0
mbed-hal-k64f 1.0.1
mbed-hal-ksdk-mcu 1.0.3
mbed-hal-mkit 1.0.0
mbed-hal-nordic 1.0.0
mbed-hal-nrf51822-mcu 1.0.5
mbed-hal-nrf51dk 1.0.1
mbed-hal-st 1.0.0
mbed-hal-st-stm32cubef4 1.0.2
mbed-hal-st-stm32f4 1.0.3
mbed-hal-st-stm32f429zi 1.0.3
mbed-mesh-api 1.0.1
mbed-tls-sockets 0.1.0
mbedtls 2.2.0
minar 1.0.1
minar-platform 1.0.0
minar-platform-mbed 1.0.0
sal 1.0.2
sal-driver-lwip-k64f-eth 1.0.2
sal-iface-6lowpan 1.0.7
sal-iface-eth 1.0.1
sal-stack-lwip 1.0.2
sal-stack-nanostack 3.0.5
sal-stack-nanostack-eventloop 1.0.3
sockets 1.0.2
target-frdm-k64f-armcc 1.0.0
target-frdm-k64f-gcc 1.0.1
target-kinetis-k64-armcc 1.0.0
target-kinetis-k64-gcc 1.0.0
target-mbed-armcc 0.1.2
target-mbed-gcc 0.1.3
target-nordic-nrf51822-16k-armcc 0.0.11
target-nordic-nrf51822-32k-armcc 0.0.11
target-nordic-nrf51822-16k-gcc 0.0.11
target-nordic-nrf51822-32k-gcc 0.0.8
target-nrf51dk-armcc 0.0.4
target-nrf51dk-gcc 0.0.4
target-st-stm32f429i-disco 0.0.15
ualloc 1.0.2
unity 1.0.0
uvisor-helloworld 0.7.3
uvisor-lib 1.0.6


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