The initial custom QEMU used with Eclipse.


The GNU MCU Eclipse QEMU was a fork of the public open-source QEMU project, customised for more support of Cortex-M cores, and a better integration with the GNU QEMU Debugging plug-in.

Why GNU MCU Eclipse QEMU?

QEMU is a great project, but its original focus was to emulate boards with large cores, usually application class, able to run Unix/Linux kernels. Support for bare metal Cortex-M based boards was available only for a very limited range of Cortex-M3 cores, so of little use for running tests for frameworks like µOS++ or development environments like Eclipse Embedded CDT.

Even more, support for semihosting in the public QEMU version was broken, and the verbosity required for integration with the QEMU plug-in was missing, so it could not be used with the Eclipse Embedded CDT plug-ins.

Supported boards and MCUs

The boards currently supported by the GNU MCU Eclipse QEMU are:

  • Maple – LeafLab Arduino-style STM32 microcontroller board
  • NUCLEO-F103RB – ST Nucleo Development Board for STM32 F1 series
  • NetduinoGo – Netduino GoBus Development Board with STM32F4
  • NetduinoPlus2 – Netduino Development Board with STM32F4
  • STM32-E407 – Olimex Development Board for STM32F407ZGT6
  • STM32-H103 – Olimex Header Board for STM32F103RBT6
  • STM32-P103 – Olimex Prototype Board for STM32F103RBT6
  • STM32-P107 – Olimex Prototype Board for STM32F107VCT6
  • STM32F4-Discovery – ST Discovery kit for STM32F407/417 lines
  • STM32F429I-Discovery – ST Discovery kit for STM32F429/439 lines

The following Cortex-M3 and Cortex-M4 microcontrollers are supported:

  • STM32F103RB
  • STM32F107VC
  • STM32F405RG
  • STM32F407VG
  • STM32F407ZG
  • STM32F429ZI
  • STM32L152RE

Support for the following boards is planned, but no release date is set:

  • EK-TM4C123GXL – TI Tiva C Series TM4C123GXL LaunchPad Evaluation Kit
  • FRDM-K20D50M – Freescale Freedom Development Platform for Kinetis K20 USB MCUs
  • FRDM-K22F – Freescale Freedom Development Platform for Kinetis K22 MCUs
  • FRDM-K64F – Freescale Freedom Development Platform for Kinetis K6[34] and K24 MCUs
  • FRDM-KL25Z – Freescale Freedom Development Platform for Kinetis KL[12][45] MCUs
  • FRDM-KL26Z – Freescale Freedom Development Platform for Kinetis KL[12]6 MCUs
  • FRDM-KL43Z – Freescale Freedom Development Platform for Kinetis KL[34]3, KL[12]7 MCUs
  • FRDM-KL46Z – Freescale Freedom Development Platform for Kinetis KL[34]x MCUs
  • LPCXpresso-LPC1769 – Embedded Artists LPCXpresso LPC1769 Development Board
  • NUCLEO-F334R8 – ST Nucleo Development Board for STM32 F3 series
  • NUCLEO-F411RE – ST Nucleo Development Board for STM32 F4 series
  • NUCLEO-L152RE – ST Nucleo Development Board with STM32L152RET6
  • Netduino2 – Netduino Development Board with STM32F2
  • OLIMEXINO-STM32 – Olimex Maple (Arduino-like) Development Board
  • SAM3-H256 – Olimex Header Board for ATSAM3S4BA
  • STM32F0-Discovery – ST Discovery kit for STM32F051 line
  • STM32F3-Discovery – ST Discovery kit for STM32F303 line
  • STM32VL-Discovery – ST Discovery kit for STM32F100 Value Line
  • TWR-K60F120M – Freescale Kinetis K60 120 MHz Tower System Module
  • XMC 2Go – Infineon XMC 2Go Kit with XMC1100
  • XMC1100 Boot Kit – Infineon CPU Card XMC1100 Boot Kit Entry Series
  • XMC1200 Boot Kit – Infineon CPU Card XMC1200 Boot Kit Feature Series
  • XMC1300 Boot Kit – Infineon CPU Card XMC1300 Boot Kit Control Series
  • XMC4200 Enterprise Kit – Infineon CPU Board XMC4200 Actuator
  • XMC4400 Enterprise Kit – Infineon CPU Board XMC4400 General Purpose
  • XMC4500 Enterprise Kit – Infineon CPU Board XMC4500 General Purpose
  • XMC4500 Relax Kit – Infineon CPU Board XMC4500 Relax Kit
  • XMC4500 Relax Lite Kit – Infineon CPU Board XMC4500 Relax Lite Kit

Compatibility & peripherals

The GNU MCU Eclipse QEMU maintains a certain degree of compatibility with the original qemu-system-arm, but it does not include the large Arm cores, being focused only on Cortex-M cores.

GNU MCU Eclipse QEMU is mainly intended for running tests, mainly unit tests. As such, the main compatibility requirement for the emulator was to support all devices addressed during the standard CMSIS initialisations, which generally refer to PLL & clock settings.

The next requirement was to fully support the GPIOs, at the level of allowing one or more LEDs to blink.


The blinky projects generated by the Eclipse Embedded CDT templates (and all STM32 HAL projects) use the SysTick to measure time, so any realistic emulation should support SysTick. GNU MCU Eclipse QEMU not only does this, but also provides relatively accurate time intervals, and the SysTick exception can be used from simple time measuring to driving a real-time scheduler with a reasonable number of task switches per second (1000 Hz is OK).

Semihosting and ITM

The recommended method to display messages from the target is via semihosting or ITM, both fully supported.

Writing messages via an USART is not supported.


  • QEMU accurately emulates Cortex-M3 and M4 thumb instructions; specific Cortex-M4 floating point instructions are not supported;
  • the current implementation of NVIC uses some related interrupt controller code from larger cores, and is not very accurate.

Command line options

The custom command line options are documented in the separate options page.

Future development

After the initial version proved that the idea to define peripheral register via tables is functional, it became obvious that these tables are not for humans to generate, but for machines. These definitions, in one way or another, are already available from the Arm SVD files (very large XMLs). So, for the use of QEMU, the next step is to process the SVD files and generate JSON files, with the peripheral registers, exactly as needed for a fast load by the emulator at startup. Then, from the JSON files, the run-time peripheral register objects can be generated.

There is currently no ETA for these changes, but if anyone is interested to support development, priorities might be changed.