Starboard is Cobalt's porting layer and OS abstraction. It attempts to encompass all the platform-specific functionality that Cobalt actually uses, and nothing that it does not.
Desktop Linux Cobalt is fully implemented on top of Starboard, and version 1 of the Starboard API is mostly locked down.
All source locations are specified relative to
src/starboard/ (this directory).
.- This is the root directory for the Starboard project, and contains all the public headers that Starboard defines.
examples/- Example code demonstrating various aspects of Starboard API usage.
linux/- The home of the Linux Starboard implementation. This contains a
starboard_platform.gypfile that defines a library with all the source files needed to provide a complete Starboard Linux implementation. Source files that are specific to Linux are in this directory, whereas shared implementations are pulled from the shared directory.
nplb/- “No Platform Left Behind,” Starboard's platform verification test suite.
shared/- The home of all code that can be shared between Starboard implementations. Subdirectories delimit code that can be shared between platforms that share some facet of their OS API.
Follow the Cobalt instructions, except when invoking gyp:
$ cobalt/build/gyp_cobalt -C debug linux-x64x11
and when invoking ninja:
$ ninja -C out/linux-x64x11_debug cobalt
Before starting a Cobalt/Starboard port, first you will need to define the canonical names for your set of platform configurations. These will be used when organizing the code for your platforms.
What determines what goes into one platform configuration versus another? A platform configuration has a one-to-one mapping to a production binary. So, if you will need to produce a new binary, you are going to need a new platform configuration for that.
The recommended naming convention for a
<family-name> is a name specific to the family of products you are porting to Starboard and
<binary-variant> is one or more tokens that uniquely describe the specifics of the binary you want that configuration to produce.
For example, let's say your company is named BobCo. BobCo employs multiple different device architectures so it will need to define multiple platform configurations.
All the BobCo devices are called BobBox, so it's a reasonable choice as a product
<family-name>. But they have both big- and little-endian MIPS chips. So they might define two platform configurations:
bobbox-mipseb- For big-endian MIPS devices.
bobbox-mipsel- For little-endian MIPS devices.
To be perfectly compatible with the Cobalt source tree layout, any code that is written by a party that isn't the Cobalt team should be in the
src/third_party/ directory. The choice is up to you, but we recommend that you follow this practice, even if, as we expect to be common, you do not plan on sharing your Starboard implementation with anyone.
Primarily, following this convention ensures that no future changes to Cobalt or Starboard will conflict with your source code additions. Starboard is intended to be a junction where new Cobalt versions or Starboard implementations can be replaced without significant (and hopefully, any) code changes.
We recommend that you place your code here in the source tree:
shared/- For code shared between architectures within a product family.
<binary-variant>/- For any code that is specific to a specific binary variant. Each one of these must at least have
In the BobCo's BobBox example, we would see something like:
And so on.
You can start off by copying files from a reference port to your port's location. Currently these reference ports include:
starboard_platform.gyp contains absolute paths, so the paths will still be valid if you copy it to a new directory. You can then incrementally replace files with new implementations as necessary.
The cleanest, simplest starting point is from the Stub reference implementation. Nothing will work, but you should be able to compile and link it with your toolchain. You can then replace stub implementations with implementations from
src/starboard/shared or your own custom implementations module-by-module, until you have gone through all modules.
You may also choose to copy either the Desktop Linux or Raspberry Pi ports and work backwards fixing things that don't compile or work on your platform.
For example, for
bobbox-mipsel, you might do:
mkdir -p src/third_party/starboard/bobbox cp -R src/starboard/stub src/third_party/starboard/bobbox/mipsel
Modify the files in
<binary-variant>/ as appropriate (you will probably be coming back to these files a lot).
<binary-variant>/starboard_platform.gyp to point at all the source files that you want to build as your new Starboard implementation. The
'<(DEPTH)' expression in GYP expands to enough
../s to take you to the
src/ directory of your source tree. Otherwise, files are assumed to be relative to the directory the
.gypi file is in.
In order to use a new platform configuration in a build, you need to ensure that you have a
starboard_platform.gypi in their own directory for each binary variant, plus the header files
gyp_cobalt will scan your directories for these files, and then calculate a port name based on the directories between
src/third_party/starboard and your
gyp_configuration.* files. (e.g. for
src/third_party/starboard/bobbox/mipseb/gyp_configuration.py, it would choose the platform configuration name
src/third_party/starboard/<family-name>/<binary-variant>. You may also consider copying from another reference platform, like
CreatePlatformConfig()function, pass your
<platform-configuration>as the parameter to the PlatformConfig constructor, like
'clang': 1if your toolchain is clang.
GetEnvironmentVariables, set the dictionary values to point to the toolchain analogs for the toolchain for your platform.
<platform-configuation>_<build-type>for your platform configuration name, where
<build-type>is one of
'target_arch'to your architecture:
'target_os': 'linux'if your platform is Linux-based.
'gl_type': 'system_gles2'if you are using the system EGL + GLES2 implementation.
0. This enables or disables the DIAL server that runs inside Cobalt, only when Coblat is running. You do not want in-app DIAL if you already have system-wide DIAL support.
'target_defaults'.'defines', if necessary.
configuration_public.hand adjust all the configuration values as appropriate for your platform.
starboard_platform.gypto point at all the source files you want to build as part of your new Starboard implementation (as mentioned above).
thread_types_public.has necessary to point at the appropriate shared or custom implementations.
You should now be able to run gyp with your new port. From your
$ cobalt/build/gyp_cobalt -C debug bobbox-mipseb $ ninja -C out/bobbox-mipseb_debug nplb
This will attempt to build the “No Platform Left Behind” test suite with your new Starboard implementation, and you are ready to start porting!
When bringing up a new Starboard platform, it is suggested that you try to get the NPLB tests passing module-by-module. Because of dependencies between modules, you will find it easier to get some modules passing sooner than other modules.
Here's a recommended module implementation order in which to get things going (still significantly subject to change based on feedback):