This is a setup for generating SEGA MegaDrive/Genesis ROMs using GNU utilities (gcc, ld, make, objcopy, objdump) using C language programming.

This project is in development. Nevertheless, it is already capable of compilation and ROM generation.

I will assume that user is at least somewhat experienced in C and GNU Make.

Currently, I am not sure whether it's possible to use this on Windows natively. I am working on Windows 10 Pro with Ubuntu in WSL, and I'm sure any Linux-based OS user will be able to use the generator properly, given they're capable of GCC installation.

You need to have next four packages installed:

1. Native GCC (i.e. GNU compiler that generates code for your host system)
2. GNU Make.
3. GCC for M68K.
4. GNU Binutils for M68K.

If you use Ubuntu, it's very likely you already have GCC and Make, so you may open terminal and execute this line:

sudo apt install gcc-8-m68k-linux-gnu binutils-m68k-linux-gnu

It is important to have GCC version 8. It should already be in repositories, and it has much more optimization and code generation options than GCC 7.

Just clone this repo in the place you'd like and run make there. A file ProjectName.bin will appear in your directory. This is a generated SEGA MegaDrive/Genesis ROM, and you should be able to run it with any emulator available (e.g. Kega Fusion, Regen, BlastEM).

If everything went OK, you may start writing code in main.c and add more translation units in src directory. However, if you don't want to change Makefile's innards, do not add directories in src directory, as GNU Make doesn't scan recursively.

If you open Makefile, you'll see something like this:

# Project name
PROJ := ProjectName

# Set this to 1, if you want to get listings
MAKE_LST := 0

# Set this to 1, if you want to enable optimization
OPTIMIZE := 1

# Set this to 1, if you want to enable link-time optimization
ENABLE_LTO := 0

# Output file dependencies
DEPS := startup
DEPS += intmgr

###############################################################################
# LET GNU MAKE HANDLE THE REST                                                #
###############################################################################

PROJ is just a name of generated file.

MAKE_LST, OPTIMIZE and ENABLE_LTO are self-explanatory, I believe. Be careful with LTO, though: it reduces ROM size greatly, but may ruin your program altogether. It took me quite a bit of time to tame, and I'm still not sure it behaves.

DEPS are list of dependencies of the project. By 'dependency' I mean a static library. Static library projects are located in lib directory, and they must be named exactly the same as DEPS entries.

The library project is rather unusual. Its include files are to be searched in main project folder inc. That being said, each library can depend on some other library or even the main project itself (even though I would recommend against that).

It is a good habit to introduce a separate directory in inc for each new library.

This dependency contains entry point in ROM. It performs RAM initialization (so it's possible to use global variables), calls main and freezes. This library is essential for ROM functioning.

You should never remove this dependency, unless you absolutely know what you're doing!

This dependency provides interrupt manager functionality. It allows to set interrupt handlers at runtime.

#include <m68k/intmgr.h>

void vblank_handler(void);
void hblank_handler(void);

void main(void)
{
    m68k_setih(M68KINO_LEVEL_4, &hblank_handler);
    m68k_setih(M68KINO_LEVEL_6, &vblank_handler);
}

// Definition of vblank_handler and hblank_handler...

It introduces a little bit of overhead, so you might want to define single interrupt handler at compile time. It is certainly possible, and soon there will be library for that.

If you look inside rominfo directory, you'll find there a file rominfo.c.

It contains metadata for ROM, such as system, region and game name. Change them with care.

I might write some later.