This is the documentation for the latest (main) development branch of Zephyr. If you are looking for the documentation of previous releases, use the drop-down list at the bottom of the left panel and select the desired version.

NRF52 simulated board (BabbleSim)


To allow simulating a nRF52833 SOC a Zephyr target boards is provided: the nrf52_bsim.

This uses BabbleSim to simulate the radio activity, and the POSIX architecture and the native simulator to run applications natively on the development system. This has the benefit of providing native code execution performance and easy debugging using native tools, but inherits its limitations.

This board includes models of some of the nRF52 SOC peripherals:

  • Radio

  • Timers

  • AAR (Accelerated Address Resolver)

  • AES CCM & AES ECB encryption HW

  • CLOCK (Clock control)

  • EGU (Event Generator Unit)

  • FICR (Factory Information Configuration Registers)


  • NVMC (Non-Volatile Memory Controller / Flash)

  • PPI (Programmable Peripheral Interconnect)

  • RNG (Random Number Generator)

  • RTC (Real Time Counter)

  • TEMP (Temperature sensor)

  • UART & UARTE (UART with Easy DMA)

  • UICR (User Information Configuration Registers)

and will use the same drivers as the nrf52 dk targets for these. For more information on what is modelled to which level of detail, check the HW models implementation status.

Note that unlike a real nrf52 device, the nrf52_bsim has unlimited RAM and flash for code.

Building and running

This board requires the host 32 bit C library. See POSIX Arch dependencies.

To target this board you also need to have BabbleSim compiled in your system. If you do not have it yet, the easiest way to get it, is to enable the babblesim group in your local west configuration, running west update, and building the simulator:

west config -- +babblesim
west update
cd ${ZEPHYR_BASE}/../tools/bsim
make everything -j 8


If you need more BabbleSim components, or more up to date versions, you can check the BabbleSim web page for instructions on how to fetch and build it.

You will now need to define two environment variables to point to your BabbleSim installation, BSIM_OUT_PATH and BSIM_COMPONENTS_PATH. If you followed the previous steps, you can just do:

export BSIM_OUT_PATH=${ZEPHYR_BASE}/../tools/bsim


You can add these two lines to your ~/.zephyrrc file, or to your shell initialization script (~/.bashrc), so you won’t need to rerun them manually for each new shell.

You’re now ready to build applications targeting this board, for example:

west build -b nrf52_bsim samples/hello_world

Then you can execute your application using:

$ ./build/zephyr/zephyr.exe -nosim
# Press Ctrl+C to exit

Note that the executable is a BabbleSim executable. The -nosim command line option indicates you want to run it detached from a BabbleSim simulation. This is possible only while there is no radio activity. But is perfectly fine for most Zephyr samples and tests.

When you want to run a simulation with radio activity you need to run also the BableSim 2G4 (2.4GHz) physical layer simulation (phy).

For example, if you would like to run a simple case with 1 BLE central_hr sample application connecting to a BLE peripheral sample application: Build the central_hr application targeting this board and copy the resulting executable to the simulator bin folder with a sensible name:

west build -b nrf52_bsim samples/bluetooth/central_hr
$ cp build/zephyr/zephyr.exe \

Do the same for the peripheral sample app:

west build -b nrf52_bsim samples/bluetooth/peripheral
$ cp build/zephyr/zephyr.exe \

And then run them together with BabbleSim’s 2G4 physical layer simulation:

cd ${BSIM_OUT_PATH}/bin/
./bs_nrf52_bsim_samples_bluetooth_peripheral -s=trial_sim -d=0 &
./bs_nrf52_bsim_samples_bluetooth_central_hr -s=trial_sim -d=1 &
./bs_2G4_phy_v1 -s=trial_sim -D=2 -sim_length=10e6 &

Where the -s command line option provides a string which uniquely identifies this simulation; the -D option tells the Phy how many devices will be run in this simulation; the -d option tells each device which is its device number in the simulation; and the -sim_length option specifies the length of the simulation in microseconds. BabbleSim devices and Phy support many command line switches. Run them with -help for more information.

You can find more information about how to run BabbleSim simulations in this BabbleSim example.

C library choice

These nRF bsim boards use the native simulator at their core, so you can chose with which C library you want to build your embedded code. Check the native simulator C library choice section for more info.

Debugging, coverage and address sanitizer

Just like with native_sim, the resulting executables are Linux native applications. Therefore they can be debugged or instrumented with the same tools as any other native application, like for example gdb or valgrind.

The same code coverage analysis means from the POSIX arch are inherited in this board. Similarly, the address and undefined behavior sanitizers can be used as in native_sim.

Note that BabbleSim will run fine if one or several of its components are being run in a debugger or instrumented. For example, pausing a device in a breakpoint will pause the whole simulation.

BabbleSim is fully deterministic by design and the results are not affected by the host computing speed. All randomness is controlled by random seeds which can be provided as command line options.

About time in BabbleSim

Note that time in BabbleSim is simulated and decoupled from real time. Normally simulated time will pass several orders of magnitude faster than real time, only limited by your workstation compute power. If for some reason you want to limit the speed of the simulation to real time or a ratio of it, you can do so by connecting the handbrake device to the BabbleSim Phy.