A source library xPack with the µOS++ portable startup code for bare-metal platforms
This project provides the startup source library as an xPack dependency and includes a portable startup code for bare-metal platforms.
The myth that startup code must be written in assembly because 'the C environment is not ready' is not exactly right, and, with some care to avoid undefined behaviour, can be overcome.
The 'C environment' is mainly the stack (and maybe other architecture
ABI registers, like GP on RISC-V), and this can be set in a short
assembly entry code and then the standard
_start() function can
be safely called.
The project is hosted on GitHub as micro-os-plus/startup-xpack.
This page is addressed to developers who plan to include this source library into their own projects.
For maintainer info, please see the README-MAINTAINER file.
As a source library xPack, the easiest way to add it to a project is via xpm, but it can also be used as any Git project, for example as a submodule.
For details please follow the instructions in the xPack install page.
Note: the package will be available from npmjs.com at a later date.
For now, it can be installed from GitHub:
cd my-project xpm init # Unless a package.json is already present xpm install github:micro-os-plus/startup-xpack
When ready, this package will be available as
cd my-project xpm init # Unless a package.json is already present xpm install @micro-os-plus/startup@latest ls -l xpacks/micro-os-plus-startup
If, for any reason, xpm is not available, the next recommended
solution is to link it as a Git submodule below an
cd my-project git init # Unless already a Git project mkdir -p xpacks git submodule add https://github.com/micro-os-plus/startup-xpack.git \ xpacks/micro-os-plus-startup
Apart from the unused
master branch, there are two active branches:
xpack, with the latest stable version (default)
xpack-develop, with the current development version
All development is done in the
xpack-develop branch, and contributions via
Pull Requests should be directed to this branch.
When new releases are published, the
xpack-develop branch is merged
This source xPack provides the
_startup() routine, as a replacement for
the newlib code in crt0.o or GCC code in crtbegin.o.
It is responsible for clearing the BSS, copying the DATA section, and running the static constructors.
Specific for bare-metal applications, the code also perform hardware initialisations, by calling custom hooks.
The startup source library is fully functional.
This library defines a C function that can be called from the reset handler.
void __attribute__ ((noreturn, weak)) _start (void);
Optionally it can define:
#if defined(MICRO_OS_PLUS_INCLUDE_EXIT) void __attribute__ ((weak, noreturn)) abort (void); void __attribute__ ((noreturn)) exit (int code); void __attribute__ ((weak, noreturn)) _Exit (int code); void __attribute__ ((weak, noreturn, alias ("_Exit"))) _exit (int status); #endif // MICRO_OS_PLUS_INCLUDE_EXIT
#if defined(MICRO_OS_PLUS_INCLUDE_SBRK) void* _sbrk (ptrdiff_t incr); #endif // defined(MICRO_OS_PLUS_INCLUDE_SBRK)
#if defined(MICRO_OS_PLUS_INCLUDE_STARTUP_INITIALIZE_HARDWARE_EARLY) void micro_os_plus_startup_initialize_hardware_early (void); #endif // MICRO_OS_PLUS_INCLUDE_STARTUP_INITIALIZE_HARDWARE_EARLY #if defined(MICRO_OS_PLUS_INCLUDE_STARTUP_INITIALIZE_HARDWARE) void micro_os_plus_startup_initialize_hardware (void); #endif // MICRO_OS_PLUS_INCLUDE_STARTUP_INITIALIZE_HARDWARE // A weak definition is provided here. void micro_os_plus_startup_initialize_free_store (void* heap_address, size_t heap_size_bytes); // A weak definition is provided here. The RTOS redefines it. // Called from _Exit(). void micro_os_plus_terminate_goodbye (void); // Must be defined by the device package. void __attribute__ ((noreturn)) micro_os_plus_terminate (int code);
Build & integration info
The project is written in C++, and it is expected to be used in C and C++ projects.
The source code was compiled with GCC 11, clang 12, clang 13 arm-none-eabi-gcc 11, riscv-none-elf-gcc 12, and should be warning free.
To ease the integration of this package into user projects, there are already made CMake and meson configuration files (see below).
For other build systems, consider the following details:
The following folders should be passed to the compiler during the build:
The header files to be included in user projects are:
The source files to be added to the build are:
MICRO_OS_PLUS_INCLUDE_CONFIG_H- to include
MICRO_OS_PLUS_INCLUDE_STARTUP- to include the startup code
-std=c++20or higher for C++ sources
-std=c11for C sources
@micro-os-plus/diag/tracepackage, for the tracing features
To integrate the startup source library into a CMake application, add this folder to the build:
The result is an interface library that can be added as an application dependency with:
target_link_libraries(your-target PRIVATE micro-os-plus::startup )
To integrate the startup source library into a meson application, add this folder to the build:
The result is a dependency object that can be added to an application with:
exe = executable( your-target, link_with: [ # Nothing, not static. ], dependencies: [ micro_os_plus_startup_dependency, ] )
Change log - incompatible changes
According to semver rules:
Major version X (X.y.z | X > 0) MUST be incremented if any backwards incompatible changes are introduced to the public API.
The incompatible changes, in reverse chronological order, are:
- v4.x: use newlib linker script definitions
- v3.x: rename MICRO_OS_PLUS_DEBUG
- v2.x: rename namespaces, use
- v1.x: initial release