mikrostm-link

Link together gcc and mikroC projects for STM32

Why?

This code was originally developed because I had to quickly deploy a project which I was not able to build using mikroC PRO for ARM. However, other parts of the project used hardware libraries provided by mikroC. I did not have the time to rewrite those libraries, and thus could not deploy the project using only gcc. Therefore, the solution was to create a kind of a linker to put together both projects.

Running the example

The example is meant for a STM32F407VG microcontroller, for example the one present in the mikromedia for STM32 board.

1. Install a bare metal ARM toolchain. Build your own or download a prebuilt toolchain.
2. Install libopencm3.
3. Clone this repository.
4. Go to the example/example-gcc directory, and create a symbolic link to the libopencm3 directory. For example: cd mikrostm-link/example/example-gcc && ln -s /home/user/codes/libopencm3 .
5. Go back to the example directory, and run make.
6. Program your board with the generated example.hex file using mikroe-uhb or another programmer.

What about other microcontrollers?

Other STM32 devices should be straightforward to support. Just modify FLASH_SIZE and RAM_SIZE in the first lines of the mikrostm-link file. Also, remember to modify Makefile.include and the ld script of the gcc project accordingly.

Other microcontrollers should be doable to support, but I did not care much about code extensibility. This was just a quick hack!

How do I create my own project?

This is a quick guide on how to create a pair of projects which can be linked together. Please use the example for further reference.

mikroC project

• Declare the functions which you want to import from the gcc project as function pointers. For example:

void (*const reset_handler)(void) = 0xdeadbeef;
void (*const my_function)(void) = 0xdeadbeef;

The functions can point to any address. The addresses will be modified later by mikrostm-link directly in the generated .hex file.

• The reset_handler function is always needed. It is already implemented for you, and its purpose is to call any required initialization code. You need to call this function from you mikroC project before calling any other function imported from the gcc project.

• You need to force the mikroC linker to include in its output the functions which you want to export to gcc. If the functions are not used in other parts of your mikroC project code, you can easily do this by inserting a dead code section inside your main function:

	if(0) {
		// functions imported by gcc
		asm {
			BL _HID_Read;
			BL _HID_Write;
		};
	}

• Please build your mikroC project before calling mikrostm-link. This is needed because mikrostm-link was originally designed to be used in a Linux system, with mikroC running inside a Windows VM.

gcc project

• Use our Makefile as a template. Modify it to build objects for each source file of you project. Keep the reset_handler.c file intact and always list its reset_handler.o object in the Makefile.

• Create an imports.h file containing a constant pointer to each function and to each variable which you want to import from the mikroC project. For example:

static char (*const HID_Read)(void);
static unsigned char *const readbuff;

This file will be modified by mikrostm-linker each time it runs, in order to initialize the pointers with their correct addresses.

• Create an exports.ld file containing an EXTERN declaration for each function you want to export to the mikroC project. For example:

EXTERN (do_calculation)

How does it work?

When you run mikrostm-link, it:

1. Reads symbol positions from the *.lst file generated by the mikroC compiler.
2. Creates a memory_map.ld file which instructs ld to link the gcc project only after the memory already being used by the mikroC project.
3. Modifies the imports.h file, inserting the correct addresses.
4. Runs make in the gcc project directory.
5. Glues together the .hex files generated by mikroC and by gcc, and replaces pointers to functions imported by mikroC with the correct addresses.

Which version of the compilers did you try?

• Linaro GCC 4.8-2013.07-1
• mikroC PRO for ARM version 3.3.1.0
• mikroC PRO for ARM version 4.0.0.0