PS2 homebrew #3

The next thing I wanted to do was see if I could compile the minimal android version of fluxus for the PS2. All the PS2SDK examples are written in C, and when I tried the C++ compiler at link time I got a bunch of these odd errors:

ps2-main.cpp: undefined reference to `__gxx_personality_v0′

It turns out the C++ compiler does not support exceptions so you need to add this line to the makefile:

EE_CXXFLAGS += -fno-exceptions

The other thing to get used to is one of the side effects of a machine with so many processors is that you need send lots of data around between them using DMA transfer, or direct memory access. DMA works on chunks of memory at a time, so your data needs to be aligned on particular byte boundaries. This sounds a lot more complicated than it is in practice (although it does lead to really obscure bugs if you get it wrong).

For instance, when making arrays on the heap you can do this:

struct my_struct
{
    int an_int;
    float my_array[8] __attribute__((__aligned__(16)));
    float a_float;
};

Which tells gcc to sort it out for you by forcing the pointer to my_array to fall on a 16 byte boundary.

When allocating from the heap the EE kernel provides you with a memalign version of malloc:

float *some_floats=(float*)memalign(128, sizeof(float) * 100);

The pointer some_floats will be aligned to a 128 byte boundary. This works as normal with free().

At this point, other than a few changes to tinyscheme for string functions that don’t exist on the PS2 libraries, most of the fluxus code was building. The only problem was the OpenGL ES code, as although the PS2 has some attempts at libraries that work a bit like OpenGL, the real point of playing with this machine is to write your own realtime renderer. a bit more on that next…

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