Completely open sourced ARM board

Hello every one ! I am learning how to customize Linux kernel to make it portable on embedded systems. To test my customized kernel , i want a completely open sourced ARM board . I listened about Raspberry pi but it's firmware "start.elf" is not open source. So can anybody tell me the name of the ARM board which is completely open sourced ? And can there exists any such board whose ROM/AVRAM contents can also be replaced ? Thank you !