I'm writing a little micro-kernel from scratch for my Raspberry Pi (here's the code : https://github.com/yrakcaz/RasPiK/)
Everything seems to work fine but I have just a little problem : I would like to have a file system, but I don't find out how to get the root device address. I know that, on x86 architectures, we can get the ROM address using the tags passed in argument to the main function, but I already parsed atags and there is nothing interesting...
How can I get this address?
Just choose it. Nothing is mandatory when you are bare metal. Either you get it from your bootloader, (then you have to choose it in your bootloader), or you choose to have a ramfs as the root of your file system, or you choose to use the SD card you boot on as your root file system. It's up to you.