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Silicon Labs STK3700 starter kit

Support for Silicon Labs STK3700 starter kit. More...

Detailed Description

Support for Silicon Labs STK3700 starter kit.


Silicon Labs EFM32 Giant Gecko Starter Kit is equipped with the EFM32 microcontroller. It is specifically designed for low-power applications, having energy-saving peripherals, different energy modes and short wake-up times.

The starter kit is equipped with an Advanced Energy Monitor. This allows you to actively measure the power consumption of your hardware and code, in real-time.



MCU EFM32GG990F1024
Family ARM Cortex-M3
Vendor Silicon Labs
Vendor Family EFM32 Giant Gecko
RAM 128.0 KiB
Flash 1024.0 KiB
Frequency up to 48 MHz
FPU no
MPU yes
DMA 12 channels
Timers 3x 16-bit + 1x 16-bit (low power)
ADCs, DACs 12-bit ADC, 12-bit DAC
I2Cs 2x
Vcc 1.98 V - 3.8 V
Datasheet Datasheet
Manual Manual
Board Manual Board Manual
Board Schematic Can be downloaded using Silicon Labs' Simplicity Studio


This is the pinout of the expansion header on the right side of the board. PIN 1 is the bottom-left contact when the header faces you horizontally.

3V3 20 19 RES
5V 18 17 PD7
PD6 16 15 PC6
PD5 14 13 PB12
PD4 12 11 PB11
PD3 10 9 PC5
PD2 8 7 PC4
PD1 6 5 PC3
PD0 4 3 PC0

Note**: not all starter kits by Silicon Labs share the same pinout!

Note:** some pins are connected to the board controller, when enabled!

Peripheral mapping

Peripheral Number Hardware Pins Comments
ADC 0 ADC0 CHAN0: internal temperature Ports are fixed, 14/16-bit resolution not supported
DAC 0 DAC0 CHAN0: PB11 Ports are fixed, shared with I2C
I2C 0 I2C0 SDA: PD6, SCL: PD7 I2C_SPEED_LOW and I2C_SPEED_HIGH clock speed deviate
1 I2C1 SDA: PC4, SCL: PC5 I2C_SPEED_LOW and I2C_SPEED_HIGH clock speed deviate
PWM 0 TIMER3 CHAN0: PE2 Mapped to LED0
RTT RTC Either RTT or RTC (see below)
RTC RTC Either RTC or RTT (see below)
Timer 0 TIMER0 + TIMER1 TIMER0 is used as prescaler (must be adjacent)
UART 0 UART0 RX: PE1, TX: PE0 STDIO output
1 LEUART0 RX: PD5, TX: PD4 Baud rate limited (see below)

User interface

Peripheral Mapped to Pin Comments
Button PB0 PB9
PB1 PB10
LED1 PE3 Yellow LED

Implementation Status

Device ID Supported Comments
MCU EFM32GG yes Power modes supported
Low-level driver ADC yes
DAC yes
Flash yes
GPIO yes Interrupts are shared across pins (see reference manual)
HW Crypto yes
I2C yes
PWM yes
RTC yes As RTT or RTC
SPI partially Only master mode
Timer yes
UART yes USART is shared with SPI. LEUART baud rate limited (see below)
USB no

Board configuration

Board controller

The starter kit is equipped with a Board Controller. This controller provides a virtual serial port. The board controller is enabled via a GPIO pin.

By default, this pin is enabled. You can disable the board controller module by passing DISABLE_MODULE=silabs_bc to the make command.

Note:** to use the virtual serial port, ensure you have the latest board controller firmware installed.

Note:** the board controller always configures the virtual serial port at 115200 baud with 8 bits, no parity and one stop bit. This also means that it expects data from the MCU with the same settings.

Advanced Energy Monitor

This development kit has an Advanced Energy Monitor. It can be connected to the Simplicity Studio development software.

This development kit can measure energy consumption and correlate this with the code. It allows you to measure energy consumption on code-level.

The board controller is responsible for measuring energy consumption. For real-time code correlation, the CoreDebug peripheral will be configured to output MCU register data and interrupt data via the SWO port.

By default, this feature is enabled. It can be disabled by passing DISABLE_MODULE=silabs_aem to the make command.

Note that Simplicity Studio requires debug symbols to correlate code. RIOT-OS defaults to GDB debug symbols, but Simplicity Studio requires DWARF-2 debug symbols (-gdwarf-2 for GCC).

Clock selection

There are several clock sources that are available for the different peripherals. You are advised to read AN0004.0 to get familiar with the different clocks.

Source Internal Speed Comments
HFRCO Yes 14 MHz Enabled during startup, changeable
HFXO No 48 MHz
LFRCO Yes 32.768 kHz
LFXO No 32.768 kHz
ULFRCO No 1 kHz Not very reliable as a time source

The sources can be used to clock following branches:

Branch Sources Comments
HF HFRCO, HFXO Core, peripherals
LFA LFRCO, LFXO Low-power timers

CORELEDIV2 is a source that depends on the clock source that powers the core. It is divided by 2 or 4 to not exceed maximum clock frequencies (EMLIB takes care of this).

The frequencies mentioned in the tables above are specific for this starter kit.

It is important that the clock speeds are known to the code, for proper calculations of speeds and baud rates. If the HFXO or LFXO are different from the speeds above, ensure to pass EFM32_HFXO_FREQ=freq_in_hz and EFM32_LFXO_FREQ=freq_in_hz to your compiler.

You can override the branch's clock source by adding CLOCK_LFA=source to your compiler defines, e.g. CLOCK_LFA=cmuSelect_LFRCO.

Low-power peripherals

The low-power UART is capable of providing an UART peripheral using a low-speed clock. When the LFB clock source is the LFRCO or LFXO, it can still be used in EM2. However, this limits the baud rate to 9600 baud. If a higher baud rate is desired, set the clock source to CORELEDIV2.

Note:** peripheral mappings in your board definitions will not be affected by this setting. Ensure you do not refer to any low-power peripherals.


RIOT-OS has support for Real-Time Tickers and Real-Time Clocks.

However, this board MCU family has support for a 24-bit Real-Time Counter only, which is a ticker only. A compatibility layer for ticker-to-calendar is available, but this includes extra code size to convert from timestamps to time structures and visa versa.

Configured at 1 Hz interval, the RTC will overflow each 194 days. When using the ticker-to-calendar mode, this interval is extended artificially.

Hardware crypto

This MCUs has support for hardware-accelerated AES128 and AES256.

A peripheral driver interface is proposed, but not yet implemented.

Usage of EMLIB

This port makes uses of EMLIB by Silicon Labs to abstract peripheral registers. While some overhead is to be expected, it ensures proper setup of devices, provides chip errata and simplifies development. The exact overhead depends on the application and peripheral usage, but the largest overhead is expected during peripheral setup. A lot of read/write/get/set methods are implemented as inline methods or macros (which have no overhead).

Another advantage of EMLIB are the included assertions. These assertions ensure that peripherals are used properly. To enable this, pass DEBUG_EFM to your compiler.

Pin locations

The EFM32 platform supports peripherals to be mapped to different pins (predefined locations). The definitions in periph_conf.h mostly consist of a location number and the actual pins. The actual pins are required to configure the pins via GPIO driver, while the location is used to map the peripheral to these pins.

In other words, these definitions must match. Refer to the data sheet for more information.

Flashing the device

To flash, SEGGER JLink is required.

Flashing is supported by RIOT-OS using the command below:

make flash

To run the GDB debugger, use the command:

make debug

Or, to connect with your own debugger:

make debug-server

Some boards have (limited) support for emulation, which can be started with:

make emulate

Supported Toolchains

For using the Silicon Labs STK3700 starter kit we strongly recommend the usage of the GNU Tools for ARM Embedded Processors toolchain.

License information

Silicon Labs' EMLIB: zlib-style license (permits distribution of source).


file  board.h
 Board specific definitions for the STK3700 starter kit.
file  gpio_params.h
 Board specific configuration of direct mapped GPIOs.
file  periph_conf.h
 Configuration of CPU peripherals for the STK3700 starter kit.