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docs/develop: Detail how to add symbols to mp_fun_table for native mods.

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Thorsten von Eicken 2019-12-27 13:28:40 -08:00 committed by Damien George
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docs/develop/natmod.rst
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@ -67,6 +67,19 @@ The known limitations are:
So, if your C code has writable data, make sure the data is defined globally,
without an initialiser, and only written to within functions.
Linker limitation: the native module is not linked against the symbol table of the
full MicroPython firmware. Rather, it is linked against an explicit table of exported
symbols found in ``mp_fun_table`` (in ``py/nativeglue.h``), that is fixed at firmware
build time. It is thus not possible to simply call some arbitrary HAL/OS/RTOS/system
function, for example.
New symbols can be added to the end of the table and the firmware rebuilt.
The symbols also need to be added to ``tools/mpy_ld.py``'s ``fun_table`` dict in the
same location. This allows ``mpy_ld.py`` to be able to pick the new symbols up and
provide relocations for them when the mpy is imported. Finally, if the symbol is a
function, a macro or stub should be added to ``py/dynruntime.h`` to make it easy to
call the function.
Defining a native module
------------------------