OpenBMC Hello World in SDK

Document Purpose: Walk through compiling and running an OpenBMC application in QEMU.

Prerequisites: Completed Development Environment Setup Document

Clone and Build a Repo

This lesson uses openbmc/phosphor-state-manager repo. To keep your repos organized, it's a good idea to keep them all under some common directory like ~/Code/.

  1. Clone the Repository
git clone https://github.com/openbmc/phosphor-state-manager.git
  1. Add code to print out a Hello World
cd phosphor-state-manager
vi bmc_state_manager_main.cpp

Your diff should look something like this:

+#include <iostream>

 int main(int argc, char**)
 {
@@ -17,6 +18,8 @@ int main(int argc, char**)

     bus.request_name(BMC_BUSNAME);

+    std::cout<<"Hello World" <<std::endl;
+
     while (true)
     {
  1. Build the Repository

This is a meson based repository

meson build
ninja -C build

Load the Application Into QEMU

  1. Strip the binary you generated

OpenBMC is an embedded environment so always best to load on the smallest size application/library

arm-openbmc-linux-gnueabi-strip phosphor-bmc-state-manager
  1. Create the directory in your QEMU session for you to copy your binary too

OpenBMC overrides the PATH variable to always look in /usr/local/bin/ first so that's where we put patches for testing. From your QEMU session:

mkdir -p /usr/local/bin
  1. scp this binary onto your QEMU instance

If you used the default ports when starting QEMU then here is the scp command to run from your phosphor-state-manager directory. If you chose your own port then substitute that here for the 2222.

scp -P 2222 phosphor-bmc-state-manager root@127.0.0.1:/usr/local/bin/

Run the Application in QEMU

  1. Stop the BMC state manager service
systemctl stop xyz.openbmc_project.State.BMC.service
  1. Run the application in your QEMU session:
phosphor-bmc-state-manager

You'll see your "Hello World" message displayed. Ctrl^C to end that application. In general, this is not how you will test new applications. Instead, you'll be using systemd services.

  1. Start application via systemd service

OpenBMC uses systemd to manage its applications. There will be later tutorials on this, but for now just run the following to restart the BMC state service and have it pick up your new application:

systemctl restart xyz.openbmc_project.State.BMC.service

Since systemd started your service, the "Hello World" will not be output to the console, but it will be in the journal. Later tutorials will discuss the journal but for now just run:

journalctl | tail

You should see something like this in one of the journal entries:

<date> romulus phosphor-bmc-state-manager[1089]: Hello World

That's it! You customized an existing BMC application, built it using the SDK, and ran it within QEMU!