Wednesday, July 14, 2010

Cross compiling the Linux kernel from Mac OS X

So I picked up a 13" MacBook and have been fiddling around with it. I like it, sue me.

One of the first things I did (as any Linux developer would) was to install darwin ports. I noticed some interesting things in there. A few that I needed (git) and a few that completely surprised me (dpkg and apt).

One thing that was missing was a Linux cross-compiler. So I did what any self-respecting Linux developer on a Mac would do: I built one.

Don't get too excited. I've only built one worthy of compiling a kernel (which means no C library, no userspace, etc).

The result of my work is here (built on 10.6.3):

You may notice the extra elf.h file, which is needed in /usr/include/elf.h for some programs in the kernel to compile natively on the host (e.g. modpost). The gcc and binutils will unpack in /opt/local/.

In order to cross-compile, you will need to add a few things to your kernel make command line:

make ARCH=x86_64 CROSS_COMPILE=x86_64-linux-gnu- ...

You may notice, like I did, scripts/genksyms/parse.c has a #include for malloc.h which is not on Darwin. You may safely delete that line.

Note that you must already have /opt/local/bin in your PATH. Using ARCH=i386 will also work and compile 32-bit kernels. One last point, the sources for gcc/binutils came from Ubuntu's Jaunty.

Happy hacking...

Thursday, July 1, 2010

Oldies but goodies: libugci

So I went digging around my old software, and ran across some interesting stuff that doesn't get a lot of attention. I've picked out one in particular that I haven't heard much about in a long time, but I consider it very useful for people who love MAME: libugci

I had built an arcade cabinet a long time ago that was making use of a USB control interface called Happ UGCI. It allows you to directly interface real video game style controls (buttons, joysticks, trackball, coin door, etc) with a PC.

It was perfect for that I was doing, except that it sucked on Linux. Back then, I actually had to write some patches for the kernel to get it all working correctly (firmware bugs in the UGCI). In addition, much of it was not accessible via USB input layer, and so I wrote a library called libugci that took advantage of the HID interface to the board.

The board allows you to connect a real coin-door, and libugci+mame will convert that to coin-door events in the software. I always wanted to complete my MAME cabinet with a coin-door so I could make money off my friends :)

The MAME code has support for libugci built-in (thanks to my patches submitted all those years ago). Installing libugci, and recompiling MAME with this support enabled will make use of it. There are also some programs for accessing the EEPROM on the board, as well as mapping events from UGCI to HID keyboard strokes (in cases where you would want that as opposed to real joy/mouse events).

So if you're a MAME junky like I am, and need that extra bit of features that only the UGCI can offer, you can download the library from:

  • Tarball
  • git://

Good luck and happy gaming!