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##Some background## The most important thing you should know is that the RaspberryPi is a strange beast where the ARM CPU is the not main CPU - it's only a co-processor to the VideoCore GPU. When the RaspberryPi starts, a GPU blob is read from the SD card to the L2 cache and executed. This code then brings up all the important peripherals (RAM, clocks etc) and starts the ARM CPU. Then the 2nd stage bootloader or some operating system itself can be run on ARM CPU.

Some background

The most important thing you should know is that the RaspberryPi is a strange beast where the ARM CPU is the not main CPU - it's only a co-processor to the VideoCore GPU. When the RaspberryPi starts, a GPU blob is read from the SD card to the L2 cache and executed. This code then brings up all the important peripherals (RAM, clocks etc) and starts the ARM CPU. Then the 2nd stage bootloader or some operating system itself can be run on ARM CPU.

I don't know any other board as good as RaspberryPi so it's hard to recommend something but you may take a look at some mature projects like Beagleboard/Beaglebone/Pandaboard or you can follow the development of some new boards like the Cubieboard. It all depends on what exactly you want to accomplish.

I don't know any other board as good as RaspberryPi so it's hard to recommend something but you may take a look at some mature projects like OMAP based Beagleboard/Beaglebone/Pandaboard or you can follow the development of some new boards like the Allwinner based Cubieboard or PCduino. It all depends on what exactly you want to accomplish.

VideoCore is proprietary, there is no official documentation and development tools. So unless you want to put a lot of effort, you can't rewrite VCOS with your own code. Another problem is that the USB stack by Synopsys is proprietary and again there is no documentation for it and it seems that even with documentation it's hard to implement it reliably. But again, the code is available (linux kernel, u-boot, CSUD). Using advanced graphics capabilities of Video Core may also be hard - there is some open source code for the graphics libraries, but it's only for the ARM side.

VideoCore is proprietary, there is no official documentation and development tools. So unless you want to put a lot of effort, you can't rewrite VCOS with your own code. There is, however, some effort to reverse engineer the Video Core, you can find some information here.

Another problem is that the USB stack by Synopsys is proprietary and again there is no documentation for it and it seems that even with documentation it's hard to implement it reliably. But again, the code is available (Linux kernel, u-boot, CSUD). Using advanced graphics capabilities of Video Core may also be hard - there is some open source code for the graphics libraries, but it's only for the ARM side.