It is a BSD Open Source License. This is a non-viral license, only asking that if you use it, you acknowledge the authors, in this case UC Berkeley. We have not filed nor do we intend to file any patents that would be required to implement a RISC-V-compatible processor. While we know of no patents that are required to implement the RISC-V ISA, there are many microarchitectural patents that might be infringed by a particular RISC-V implementation. We cannot indemnify users against ISA or implementation patents asserted by others.