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EFM32 is a family of 32-bit microcontroller integrated circuits by Energy Micro AS, a subsidiary of Silicon Labs. The EFM32 chips are grouped into related series that are based around the same 32-bit ARM processor core, such as the Cortex-M4F, Cortex-M3, or Cortex-M0+. Internally, each microcontroller consists of the processor core, static RAM memory, flash memory, debugging interface, and various peripherals.

EFM32 is a mixed-signal microcontroller focusing on supporting ultra low power battery operated solutions.[1][2] To run from small cell batteries, EFM32 MCUs incorporates low power peripheral technology, fast response time, low latency, and autonomous operation (i.e. the CPU does not run while the peripherals communicate).[3] The EFM32 microcontrollers are offered in various configurations.[4]

EFM Tiny Gecko in 24 and 32 pin QFN packages.


Gecko logo
Main articles: ARM architecture and ARM Cortex-M

The central processing unit in EFM32 is based on either Cortex-M4F,[5] Cortex-M3,[6] or Cortex-M0[7] processor core from ARM Holdings. EFM stands for Energy Friendly Microcontrollers and the number 32 indicates the 32-bit processor core.

EFM32 devices main areas are in the low power industrial and consumer battery powered applications.[8] This typically consist of energy metering, alarms and security systems, consumer products, communication and computer networking systems, industrial sensors, and portable medical- and sport/fitness solutions.

Gecko name[edit]

EFM32 microcontroller families are named after Gecko lizards. These chips have a logo of them, inspired by David Attenborough and the BBC camera crew that made a series on amphibians and reptiles.[9] These vertebrates consumes 10% energy of a mammal of similar size. Hence, the Gecko name is used to indicate the ultra-low power characteristics of EFM32 MCUs.[10]

EFM32 technology[edit]

EFM32 Gecko from Energy Micro

EFM32 microcontrollers target very low active power consumption, reduced processing time, very fast wake-up time and ultra-low standby current. To achieve such characteristics, Energy Micro has listed 10 factors for microcontroller design improvements:[11]

  1. Very low active power consumption: EFM32 microcontrollers target significantly reduced active mode power consumption. At 32 MHz and 3V the MCU consumes 180 μA/MHz while running real life code from the internal Flash memory.
  2. Reduced processing time: Energy Micro build the EFM32 Gecko microcontroller using the 32-bit ARM Cortex-M3 processor core, which ARM developed for response and power sensitive applications. Tasks can therefore be executed with few clock cycles, which dramatically reduces the active period.
  3. Very fast wake-up time: Low power systems continually switch between active- and sleep modes. By minimizing the inefficient wake-up period between deep sleep modes and active mode as little energy as possible is used before the CPU starts processing its tasks.
  4. Ultra-low standby current: Low energy usage in standby modes while still performing basic operations is useful for low power applications, and the sleep modes includes RAM and CPU retention, Power-on Reset and Brown-out Detection safety features plus and a Real Time Counter.
  5. Autonomous peripheral operation: The EFM32 peripherals can operate in low energy modes without using the CPU. Using autonomous peripherals, an application can reduce power consumption while still performing very advanced tasks.
  6. PRS - Peripheral Reflex System: It is possible to directly connect one peripheral to another peripheral without involving the CPU. With this system a peripheral can produce signals that other peripherals can consume and instantly react to while the CPU remains asleep.
  7. Well designed Energy Modes: EFM32 microcontrollers have five efficient energy modes, which gives system designers the flexibility to optimize their application for highest performance and longer battery life.
  8. Energy efficient peripherals include: a LCD controller driving 4x40 segments at only 0.55 uA, a Low Energy UART performing full communication at 32 kHz while consuming only 100 nA, a 12-bit ADC performing 1 million samples/sec at only 200 uA, the Analog Comparator using as little as 150 nA, the Hardware accelerator for 128/256-bit AES key encryption and decryption in only 54/75 cycles
  9. AEM - Advanced Energy Monitoring: The Advanced Energy Monitoring system makes it possible to accurately view a prototype's current consumption data in real time, enabling early identification and removal of adverse current drains. The tools also integrate a full J-Link from Segger, for easy debugging and programming.
  10. energyAware Software: The free energyAware software suite supports the EFM32 Gecko development tools. This includes code examples, CMSIS libraries and a Profiler that reads the kits Advanced Energy Monitoring (AEM) system data and enables simple graphical visualization and optimization of application energy consumption and code.

Energy modes[edit]

A wide selection of energy modes available in the EFM32 makes it possible to optimize a systems energy consumption to meet low energy requirements both in active- and sleep modes. The very short transition time between the energy modes in combination with the autonomous operation in the low energy modes favor long sleep times. In all but the deepest energy mode application data is maintained with full RAM retention.[12]

In active mode the industry standard Cortex-M3 RISC processor delivers high performance in terms of computational performance, system response, and low power consumption. Challenging tasks are handled by the processor and the highly integrated peripherals, and the fast interrupt handling and low latency makes the EFM32 very well suited for battery operated applications and systems with critical response times.

Autonomous peripherals[edit]

EFM32 microcontrollers use various control techniques for efficient energy management. Low power and customizable peripherals surround the powerful 32-bit ARM Cortex-M3 processor and enable fast autonomous operation and reduce the need for CPU. High overall integration reduce a systems need for external components. Peripherals can react and respond to input from external or internal triggers without any CPU intervention via a system called the Peripheral Reflex System.[13]


The EFM32 microcontroller family is one of the two products of Energy Micro. The other being EFR4D Draco SoC radios.

  • In April 2008, Energy Micro announced that it licensed the ARM Cortex-M3 core.[14]
  • In October 2009, Energy Micro announced EFM32 Gecko MCU family (EFM32G series) based on Cortex-M3.[15]
  • In December 2009, Energy Micro announced development kit for its EFM32 Gecko MCU family.[16]
  • In February 2010, Energy Micro announced EFM32 Tiny Gecko MCUs were announced.[17]
  • In March 2010, Energy Micro announced EFM32 Tiny Gecko MCU family (EFM32TG series) based on Cortex-M3.[18]
  • In March 2010, Energy Micro announced low cost EFM32 Gecko starter kit.[19]
  • In July 2010, Energy Micro announced EFM32 Giant Gecko MCU family (EFM32GG series) based on Cortex-M3 for memory heavy applications.[20]
  • In November 2010, Energy Micro announced Simplicity Studio development suite.[21]
  • In March 2011, Energy Micro announced EFM32 Zero Gecko MCU family (EFM32ZG series) based on Cortex-M0+ for low cost applications.[22]
  • In September 2011, Energy Micro announced EFM32 Leopard Gecko MCU Family (EFM32LG series) based on Cortex-M3.[23]
  • In April 2013, Enery Micro announced EFM32 Wonder Gecko MCU family (EFM32WG series) based on ARM Cortex-M4F.[24]
  • In June 2013, Silicon Labs announced intention to acquire Energy Micro.[25][26]


Like many other modern 32-bit RISC microcontrollers, EFM32 includes peripherals like GPIO, ADC, DAC, Timer/Counter, Watchdog Timer, UART, I²C Interface, SPI Interface, RTC. Many of these peripherals can work without CPU's intervention thereby reducing overall power consumption.

These microcontrollers are available in QFN16/24/32/64, QFP48/100 and BGA112/120 packages.


  • Configurable GPIO drive strength (up to 20mA)
  • Special bus called Peripheral Reflex System (PRS) routes events from one peripheral to another without CPU's intervention.
  • Low Energy Sensor Interface (LESENSE peripheral) useful for capacitive / inductive sensing. LESENSE is capable of independent decision making (i.e. analog signal level comparison) and wakes up the CPU only when necessary.
  • Autonomous and low energy peripherals.
  • Different sleep modes.

Product families[edit]

EFM32 MCUs are classified into seven categories:[27]

  • Zero Gecko - the EFM32ZG series
    • ARM Cortex-M0+ processor core
    • Up to 24 MHz operation
    • 4-32 kB program memory, 2-4 kB RAM
  • Happy Gecko - the EFM32HG series
    • ARM Cortex-M0+ processor core
    • Up to 25 MHz operation
    • 32-64 kB program memory, 4-8 kB RAM
  • Tiny Gecko - the EFM32TG Series
    • ARM Cortex-M3 processor core
    • Up to 32 MHz operation
    • 4-32 kB program memory, 2-4 kB RAM
    • Includes devices with LCD, LESENSE, OPAMP, AES peripherals
  • Gecko - the EFM32G Series
    • ARM Cortex-M3 processor core
    • Up to 32 MHz operation
    • 16-128 kB program memory, 8-16 kB RAM
    • Includes devices with LCD and AES peripherals
  • Leopard Gecko - the EFM32LG Series
    • ARM Cortex-M3 processor core
    • Up to 48 MHz operation
    • 64-256 kB program memory, 32 kB RAM
    • Includes devices with USB, LCD, TFT, LESENSE, OPAMP and AES peripherals
  • Giant Gecko - the EFM32GG Series
    • ARM Cortex-M3 processor core
    • Up to 48 MHz operation
    • 512-1024 kB program memory, 128 kB RAM
    • Includes devices with USB, LCD, TFT, LESENSE, OPAMP and AES peripherals
  • Wonder Gecko - the EFM32WG Series
    • ARM Cortex-M4F with FPU processor core
    • Up to 48 MHz operation
    • 64-256 kB program memory, 32 kB RAM
    • Includes devices with USB, LCD, TFT, LESENSE, OPAMP and AES peripherals

Development boards[edit]

Energy Micro Wonder Gecko STK Board with Energy Micro EFM32WG990

The following starter kits and development kits are sold by Energy Micro to provide a quick and easy way for engineers to evaluate their microcontroller chips. These starter kits are available from various distributors for USD$69. Each board includes an on-board Segger J-link SWD debugger programming and debugging via a MiniUSB connector. The power for each board is provided by a choice of the 5 V via the USB cable, or external 3.0 V via a CR2032 battery.

Starter kits[edit]

  • EFM32-G8XX-STK [28]
  • EFM32-TG-STK3300 [29]
  • EFM32-GG-STK3600 [30]
  • EFM32-GG-STK3700 [31]
  • EFM32-WG-STK3800 [32]

Development kits[edit]

Development tools[edit]



The EFM32 tools are named "energyAware" and include hardware and software from Energy Micro in addition to third party tools from companies like IAR Systems,[39] Keil,[40] Rowley Associates,[41] Segger,[42] Olimex,[43] RK-SYSTEM.[44] The energyAware Profiler is an energy debugging tool that use data from the development kits to display real-time profiling and debugging information of the associated object code. In addition the energyAware Designer generates the initial code for the EFM32 package options, and the user may set up, enable and disable peripherals by clicking on the chosen package. The energyAware Software is available for free from Energy Micro's software page.


The amount of documentation for all ARM chips is daunting, especially for newcomers. The documentation for microcontrollers from past decades would easily be inclusive in a single document, but as chips have evolved so has the documentation grown. The total documentation is especially hard to grasp for all ARM chips since it consists of documents from the IC manufacturer (Energy Micro / Silicon Labs) and documents from CPU core vendor (ARM Holdings).

A typical top-down documentation tree is: manufacturer website, manufacturer marketing slides, manufacturer datasheet for the exact physical chip, manufacturer detailed reference manual that describes common peripherals and aspects of a physical chip family, ARM core generic user guide, ARM core technical reference manual, ARM architecture reference manual that describes the instruction set(s).

EFM32 documentation tree (top to bottom)
  1. EFM32 website.
  2. EFM32 marketing slides.
  3. EFM32 datasheet.
  4. EFM32 reference manual.
  5. ARM core website.
  6. ARM core generic user guide.
  7. ARM core technical reference manual.
  8. ARM architecture reference manual.

Energy Micro (Silicon Labs) has additional documents, such as: evaluation board user manuals, application notes, getting started guides, software library documents, errata, and more. See External Links section for links to official EFM32 and ARM documents.

See also[edit]


  1. ^ ARM Low Power Design
  2. ^ Can ARM's Cortex-M3 processor save the planet?
  3. ^ EFM32 Technology
  4. ^ EFM32 MCU products named "Zero Gecko", ""Tiny Gecko", "Gecko" ,"Leopard Gecko" and "Giant Gecko"
  5. ^ EFM32 ARM Cortex-M4F
  6. ^ EFM32 ARM Cortex-M3
  7. ^ EFM32 ARM Cortex-M0+
  8. ^ Application Areas
  9. ^ Life In Cold Blood; David Attenborough; BBC.
  10. ^ EFM32 Brochure : Why is EFM32 called Gecko
  11. ^ "10 factors that make the 32-bit EFM32 the world's most energy friendly microcontroller". Energy Micro. Retrieved 2013-08-23. 
  12. ^ Energy Micro: EFM32 Energy Modes
  13. ^ Energy Micro: EFM32 Peripheral Set
  14. ^ Energy Micro Licenses Cortex-M3 Processor
  15. ^ Press Release; Energy Micro; October 21, 2009
  16. ^ Press Release; Energy Micro; December 16, 2009
  17. ^ EETIMES on EFM32 Tiny Gecko
  18. ^ Press Release; Energy Micro; March 2, 2010
  19. ^ Energy Micro launches starter kit for energy friendly microcontroller range
  20. ^ Energy Micro adds Giant Gecko microcontroller for memory heavy applications
  21. ^ Press Release; Energy Micro; November 9, 2010
  22. ^ Press Release; Energy Micro; March 2, 2011
  23. ^ Press Release; Energy Micro; September 28, 2011
  24. ^ [1]
  25. ^ Silicon Labs to Acquire Energy Micro
  26. ^ Silicon Labs to Acquire Energy Micro- A leader in low power ARM Corex-based microcontrollers and radios
  27. ^ EFM32 Gecko product list
  28. ^ EFM32-G8XX-STK Kit
  29. ^ EFM32-TG-STK3300 Kit
  30. ^ EFM32-GG-STK3600 Kit
  31. ^ EFM32-GG-STK3700 Kit
  32. ^ EFM32-WG-STK3800 Kit
  33. ^ EFM32-G2XX-DK Kit
  34. ^ EFM32-G8XX-DK Kit
  35. ^ EFM32G-DK3550 Kit
  36. ^ EFM32LG-DK3650 Kit
  37. ^ EFM32GG-DK3750 Kit
  38. ^ EFM32WG-DK3850 Kit
  39. ^ IAR Systems
  40. ^ Keil
  41. ^ Rowley Associates
  42. ^ Segger
  43. ^ Olimex
  44. ^ RK-SYSTEM

Further reading[edit]

External links[edit]

EFM32 Official Documents
ARM Official Documents