emBIOS is best described as a hardware abstraction with threading and debugging capabilities built in. It simplifies development immensely by integrating drivers for all the iPods. Before drivers were scattered throughout multiple tools built for multiple iPods. If there was a bug fix for a driver, it would have to be applied in many different places. emBIOS attempts to solve this problem by providing a syscall interface that is standard throughout all iPod generations. This means that a build of a tool can work across generations as long as it is run on a native emBIOS. This allows for maximum code reuse.
If you're curious about how emBIOS works, you can browse it's SVN here.
If you want to try it out on your own iPod, there are automatic builds on our buildserver, but you might as well just check out the SVN and compile it yourself. After all, emBIOS itself doesn't do much except print out its version string to the console. You must put something in main.c if you want it to do anything. Here are the basic steps to getting emBIOS up and running on your iPod:
- Check out the Freemyipod SVN.
- Build the UCL tool in the folder tools/ucl of the SVN using make and copy those tools to a place in your path.
- Make sure you have the arm-eabi toolchain. You can easily build this using the rockboxdev.sh script in the tools directory of the Rockbox SVN.
- You can compile emBIOS for all targets ('make') or for only some ('make target1 target2'). You can find out the target names on the buildserver
- If your toolchain prefix is not 'arm-none-eabi-' but something different (like 'arm-elf-eabi-' if you compile it with a toolchain created with the rockboxdev script) you can set the CROSS variable to your prefix.
So to compile for the iPod nano 2g with your toolchain prefixed with arm-elf-eabi- do:
CROSS=arm-elf-eabi- make ipodnano2g