None OS SDK

When building with framework = noneos-sdk, several build options are available for the platformio.ini.

Link Time Optimization (LTO)

To activate LTO in the compiling and linking stage, use

board_build.use_lto = yes

Startup File

By default, a slightly modified startup file (e.g., startup_ch32v30x_D8.S) will be used. If you want to use a startup file that you explicitly placed in the project, turn off the compilation of the built-in one using

board_build.use_builtin_startup_file = no

System / Startup Code

By default, the built-in system_ch32v<series>.c will be used (example). This file contains the clock setup code and by-default uses the HSE as clock source, thus needing an external crystal oscillator connected to the chip to function correctly.

If you want to use a system file that you explicitly placed in the project that has the correct settings, turn off the compilation of the built-in one using

board_build.use_builtin_system_code = no

Debug Code

By default, the built-in debug.c will be compiled in the project (example). The code in this file contains

1. delay functions

2. UART initialization functions

3. _write implementation (for making e.g. printf work, writes data for stdout to actual UART registers)

4. _sbrk implementation (needed for malloc and free functions to allocate new memory)

While this is convenient as default, in your project you might want to have full control over these implementations.

To turn off the compilation of the built-in debug implementation, use

board_build.use_builtin_debug_code = no

C++ Support

By default, C++ support is disabled.

To be able to use C++ properly, meaning that constructors of global objects are called etc., one would usually need to do adaptions to the startup file (calling __libc_init_array) and add a _fini and _init implementation.

To make things easier, we have already done these modifications in an activatable way. To turn on C++ support, simple use

board_build.cpp_support = yes

This technically defines __PIO_CPP_SUPPORT__ which the built-in startup file will react to and also compiles our cpp_support.c file with _weak overridable _fini and _init functions.