Michał Michał - 3 years ago 216
C Question

How can I use one function from main application and bootloader? (embedded)

First of all I need to say I develop application for embedded device based on cortex m4.

I have functions that are common for bootloader and main application. For now I compile source files 2 times once for bootloader and app. But I am running short on space for dual bank dfu and I would like to have those functions only once in ROM. Any idea how can I achieve this?


Using functions pointers maybe danger in some cases, check on my problems - Using pointer functions - 2 seperate applications on 1 device

Answer Source

This is only a partial answer and assumes you can jump into your bootloader from your main code using the same address space. Then, a common technique is to provide your "bootloader API" as a table of function pointers.

Say for example you have the following functions in your bootloader:

static int do_something(void)
    return 42;

static int do_something_else(int arg)
    return arg+5;

Then you would declare your API in a header like this:

struct bootloaderApi
    int (*do_something)(void);
    int (*do_something_else)(int arg);

In the implementation of your bootloader, you define this table in its own section:

// this is GCC syntax, use whatever your compiler provides to specify the section
struct bootloaderApi api __attribute__((section("API"))) = {

Then when building the bootloader, make sure your section is placed at a suitable fixed address. When e.g. using the GNU linker, you could have something like this in your linker script:

  // standard sections, e.g.:
  .text : { *(.text) }
  .data : { *(.data) } 
  .bss :  { *(.bss)  *(COMMON) }

  // your API table:
  .API 0x10000 : { *(.API) }

This now assumes your API table will be placed at 0x10000. Then you could do the following to access the API from your main code:

struct bootloaderApi *api = (struct bootloaderApi *)0x10000;


All of this is just a sketch to give you an idea how to do this in a sensible way. It will heavily depend on your target platform and the toolchain you're using.

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