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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, So, if your C code has writable data, make sure the data is defined globally,
without an initialiser, and only written to within functions. 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 Defining a native module
------------------------ ------------------------