NRF52 simulated board (BabbleSim)

Overview

This is a simulated NRF52 board which uses BabbleSim to simulate the radio activity. This board models some of the NRF52 SOC peripherals:

  • Radio
  • Timers
  • Real time counter
  • Random number generator
  • AES CCM & AES ECB encryption HW
  • Accelerated address resolver
  • Clock control
  • PPI (Programmable Peripheral Interconnect)

The nrf52_bsim board definition uses the POSIX architecture to run applications natively on the development system. As with the native_posix board, this has the benefit of providing native code execution performance and easy debugging using native tools, but has the same drawbacks. Please refer to Native Posix’s important limitations for more details.

Building and running

Note

You must have the 32-bit C library installed in your system (in Ubuntu 16.04 install the gcc-multilib package)

Note

This will not work in Windows Subsystem for Linux (WSL) because WSL does not support native 32-bit binaries.

To target this board you need to have BabbleSim compiled in your system. If you do not have it yet, you can fetch and build it in this way:

mkdir -p ${HOME}/bsim && cd ${HOME}/bsim
repo init -u git@github.com:BabbleSim/manifest.git -m everything.xml \
  -b master
repo sync
make everything -j 8

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=${HOME}/bsim/
export BSIM_COMPONENTS_PATH=${HOME}/bsim/components/

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

cd $ZEPHYR_BASE/samples/hello_world
mkdir build && cd build
cmake -GNinja -DBOARD=nrf52_bsim ..
ninja

Then you can execute your application using:

$ 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:

cd $ZEPHYR_BASE/samples/bluetooth/central_hr
mkdir build && cd build
cmake -GNinja -DBOARD=nrf52_bsim ..
ninja
$ cp zephyr/zephyr.exe \
  ${BSIM_OUT_PATH}/bin/bs_nrf52_bsim_samples_bluetooth_central_hr

Do the same for the peripheral sample app:

cd $ZEPHYR_BASE/samples/bluetooth/peripheral
mkdir build && cd build
cmake -GNinja -DBOARD=nrf52_bsim ..
ninja
$ cp zephyr/zephyr.exe \
  ${BSIM_OUT_PATH}/bin/bs_nrf52_bsim_samples_bluetooth_peripheral

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.

Debugging

Just like native_posix, 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.

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.