Application Code Development

Services

The Zephyr kernel services architecture has services that are specific to the microkernel, services that are specific to the nanokernel, and services that are common, or shared, between the two.

Microkernel Services

For a complete list of microkernel services, including a description of each with code examples, see Microkernel Services.

Note

There are more microkernel services than those defined in the MDEF.

Nanokernel Services

For a complete list of nanokernel services, including a description of each with code examples, see Nanokernel Services.

Common Services

For a complete list of services common to both the nanokernel and microkernel, including a description of each with code examples, see Common Kernel Services.

Procedures and Conventions

Understanding Naming Conventions

The kernel limits the use of some prefixes to internal use only. For more information, see Code Naming Conventions.

Understanding src Directory Makefile Requirements

The src directory needs a Makefile to specify how to build the application source code. Likewise, any sub-directory within src must also have its own Makefile. The following requirements apply to all Makefiles in the src directory:

A Makefile must reference only its own files and sub-directories.
Code that references a file outside the directory cannot be included in the Makefile; the referenced file is included only in its own directory’s Makefile.
A Makefile cannot directly reference source code; it can only reference object files (.o files) produced by source code.

Note

The src directory Makefiles discussed here are distinct from the top-level application Makefile.

Adding Source Files and Makefiles to src Directories

Source code and associated Makefiles specify the how the application image is built. In a Makefile, multiple files may be referenced from a single-line entry. However, a separate line must be used to reference each directory. During the build process, Kbuild finds the source files to generate the object files by matching the file names identified in the Makefile.

Note

Source code without an associated Makefile is not included when the application is built.

Before You Begin

The Zephyr environment variable must be set for each console terminal using Common Procedures.

Steps

Create a directory structure for your source code in src and add your source code files to it.

For many useful code examples, see Common Kernel Services, Microkernel Services, and Nanokernel Services.

Create a Makefile for each src directory.
1. Use the following syntax to add file references:
```
obj-y += file.o file.o
```
2. Use the following syntax to add directory references:
```
obj-y += directory_name/**
```

Example src Makefile

This example is taken from the Philosopher’s Sample. To examine this file in context, navigate to: rootDir/samples/philosophers/microkernel/src.

obj-y = phil_fiber.o phil_task.o

Enhancing the Zephyr Kernel

When enhancing the Zephyr kernel, follow the subsystem naming conventions and the include path usage guidelines.

Subsystem Naming Conventions

In general, any sub-system can define its own naming conventions for symbols. However, naming conventions should be implemented with a unique namespace prefix (e.g. bt_ for BlueTooth, or net_ for IP) to limit possible clashes with applications. Naming within a sub-system should continue to follow prefix conventions identified above; this keeps consistent interface for all users.

Include Paths Usage Guidelines

The current build system uses a series of defs.objs to define common pieces for a specific subsystem. For example, there are common defines for all architectures under $ROOT/arch/x86, and more specific defines for each supported board within the architecture, such as, $ROOT/arch/x86/generic_pc.

Do not add every possible include paths in the defs.obj files. Too many default paths will cause problems when more than one file with the same name exists. The only include path into $vBASE/include should be $vBASE/include itself.

Files should define includes to specific files with the complete path #include subdirectory/header.h. For example, when there are two files, include/pci.h and include/drvers/pci.h, and both have been set to -Iinclude/drivers and -Iinclude for the compile, any code using #include pci.h becomes ambiguous; using the complete path #include drivers/pci.h is not. Not having -Iinclude/drivers forces users to use the second form, which is more explicit.