.. _nrf52_bsim:

NRF52 simulated board (BabbleSim)
#################################

.. contents::
   :depth: 1
   :backlinks: entry
   :local:


Overview
********

This is a :ref:`POSIX architecture<Posix arch>`
based 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, this has the benefit of
providing native code execution performance and easy debugging using
native tools, but inherits :ref:`its limitations <posix_arch_limitations>`.

.. _BabbleSim:
   https://BabbleSim.github.io

.. _nrf52bsim_build_and_run:

Building and running
**********************

This board requires the host 32 bit C library. See
:ref:`POSIX Arch dependencies<posix_arch_deps>`.

To target this board you also need to have `BabbleSim`_ compiled in your system.
If you do not have it yet, in `its web page <https://BabbleSim.github.io>`_
you can find instructions on how to
`fetch <https://babblesim.github.io/fetching.html>`_ and
`build <https://babblesim.github.io/building.html>`_ it.
In short, you can do:

.. code-block:: console

   mkdir -p ${HOME}/bsim && cd ${HOME}/bsim
   curl https://storage.googleapis.com/git-repo-downloads/repo > ./repo  && chmod a+x ./repo
   ./repo init -u https://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:

.. code-block:: console

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

.. note::

   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:

.. zephyr-app-commands::
   :zephyr-app: samples/hello_world
   :host-os: unix
   :board: nrf52_bsim
   :goals: build
   :compact:

Then you can execute your application using:

.. code-block:: console

   $ ./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:

.. zephyr-app-commands::
   :zephyr-app: samples/bluetooth/central_hr
   :host-os: unix
   :board: nrf52_bsim
   :goals: build
   :compact:

.. code-block:: console

   $ cp build/zephyr/zephyr.exe \
     ${BSIM_OUT_PATH}/bin/bs_nrf52_bsim_samples_bluetooth_central_hr

Do the same for the ``peripheral`` sample app:

.. zephyr-app-commands::
   :zephyr-app: samples/bluetooth/peripheral
   :host-os: unix
   :board: nrf52_bsim
   :goals: build
   :compact:

.. code-block:: console

   $ cp build/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:

.. code-block:: console

   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 <https://babblesim.github.io/example_2g4.html>`_.

Debugging, coverage and address sanitizer
*****************************************

Just like with :ref:`native_posix<native_posix_debug>`, 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
:ref:`code coverage analysis means from the POSIX arch<coverage_posix>`
are inherited in this board.
Similarly, the
:ref:`address sanitizers can be used as in native_posix<native_posix_asan>`.


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.

.. _handbrake device:
   https://github.com/BabbleSim/base/tree/master/device_handbrake