.. _module-pw_hdlc_lite-rpc-example:

=============================
RPC over HDLC example project
=============================
The :ref:`module-pw_hdlc_lite` module includes an example of bringing up a
:ref:`module-pw_rpc` server that can be used to invoke RPCs. The example code
is located at ``pw_hdlc_lite/rpc_example``. This section walks through invoking
RPCs interactively and with a script using the RPC over HDLC example.

These instructions assume the STM32F429i Discovery board, but they work with
any target with :ref:`pw::sys_io <module-pw_sys_io>` implemented.

---------------------
Getting started guide
---------------------

1. Set up your board
====================
Connect the board you'll be communicating with. For the Discovery board, connect
the mini USB port, and note which serial device it appears as (e.g.
``/dev/ttyACM0``).

2. Build Pigweed
================
Activate the Pigweed environment and run the default build.

.. code-block:: sh

  source activate.sh
  gn gen out
  ninja -C out

3. Flash the firmware image
===========================
After a successful build, the binary for the example will be located at
``out/<toolchain>/obj/pw_hdlc_lite/rpc_example/bin/rpc_example.elf``.

Flash this image to your board. If you are using the STM32F429i Discovery Board,
you can flash the image with `OpenOCD <http://openocd.org>`_.

.. code-block:: sh

 openocd -f targets/stm32f429i-disc1/py/stm32f429i_disc1_utils/openocd_stm32f4xx.cfg \
     -c "program out/stm32f429i_disc1_debug/obj/pw_hdlc_lite/rpc_example/bin/rpc_example.elf"

4. Invoke RPCs from in an interactive console
=============================================
The RPC console uses `IPython <https://ipython.org>`_ to make a rich interactive
console for working with pw_rpc. Run the RPC console with the following command,
replacing ``/dev/ttyACM0`` with the correct serial device for your board.

.. code-block:: text

  $ python -m pw_hdlc_lite.rpc_console --device /dev/ttyACM0

  Console for interacting with pw_rpc over HDLC.

  To start the console, provide a serial port as the --device argument and paths
  or globs for .proto files that define the RPC services to support:

    python -m pw_hdlc_lite.rpc_console --device /dev/ttyUSB0 sample.proto

  This starts an IPython console for communicating with the connected device. A
  few variables are predefined in the interactive console. These include:

      rpcs   - used to invoke RPCs
      device - the serial device used for communication
      client - the pw_rpc.Client

  An example echo RPC command:

    rpcs.pw.rpc.EchoService.Echo(msg="hello!")

  In [1]:

RPCs may be accessed through the predefined ``rpcs`` variable. RPCs are
organized by their protocol buffer package and RPC service, as defined in a
.proto file. To call the ``Echo`` method is part of the ``EchoService``, which
is in the ``pw.rpc`` package. To invoke it synchronously, call
``rpcs.pw.rpc.EchoService.Echo``:

.. code-block:: python

    In [1]: rpcs.pw.rpc.EchoService.Echo(msg="Your message here!")
    Out[1]: (<Status.OK: 0>, msg: "Your message here!")

5. Invoke RPCs with a script
============================
RPCs may also be invoked from Python scripts. Close the RPC console if it is
running, and execute the example script. Set the --device argument to the
serial port for your device.

.. code-block:: text

  $ pw_hdlc_lite/rpc_example/example_script.py --device /dev/ttyACM0
  The status was Status.OK
  The payload was msg: "Hello"

  The device says: Goodbye!