pw_hdlc: RPC over HDLC example project#

The pw_hdlc module includes an example of bringing up a pw_rpc server that can be used to invoke RPCs. The example code is located at pw_hdlc/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 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.

. ./activate.sh
pw package install nanopb
gn gen out --args='dir_pw_third_party_nanopb="//environment/packages/nanopb"'
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/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.

openocd -f \
  targets/stm32f429i_disc1/py/stm32f429i_disc1_utils/openocd_stm32f4xx.cfg \
  -c "program \
  out/stm32f429i_disc1_debug/obj/pw_hdlc/rpc_example/bin/rpc_example.elf \
  verify reset exit"

4. Invoke RPCs from in an interactive console#

The RPC console uses pw_console 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.

pw-system-console --no-rpc-logging --proto-globs pw_rpc/echo.proto \
  --device /dev/ttyACM0

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:

>>> device.rpcs.pw.rpc.EchoService.Echo(msg='Hello, world!')
(Status.OK, pw.rpc.EchoMessage(msg='Hello, world!'))

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.

python pw_hdlc/rpc_example/example_script.py --device /dev/ttyACM0

You should see this output:

The status was Status.OK
The payload was msg: "Hello"

The device says: Goodbye!

Local RPC example project#

This example is similar to the above example, except it uses a socket to connect a server and a client running on the host.

1. Build Pigweed#

Activate the Pigweed environment and build the code.

. ./activate.sh
pw package install nanopb
gn gen out --args='dir_pw_third_party_nanopb="//environment/packages/nanopb"'
ninja -C out

2. Start client side and server side#

Run pw_rpc server in one terminal window.

./out/pw_strict_host_clang_debug/obj/pw_hdlc/rpc_example/bin/rpc_example

In a separate activated terminal, run the pw-system-console RPC client with --proto-globs set to pw_rpc/echo.proto. Additional protos can be added if needed.

pw-system-console --no-rpc-logging --proto-globs pw_rpc/echo.proto \
  --socket-addr default

Tip

The --socket-addr may be replaced with IP and port separated by a colon, for example: 127.0.0.1:33000; or, if using a unix socket, the path to the file follows “file:”, for example file:/path/to/unix/socket. Unix socket Python support is pending https://bugs.python.org/issue33408.

Tip

The default RPC Channel ID (1) can be overriden with --channel-id.

Then you can invoke RPCs from the interactive console on the client side.

>>> device.rpcs.pw.rpc.EchoService.Echo(msg='Hello, world!')
(Status.OK, pw.rpc.EchoMessage(msg='Hello, world!'))