Building Hello World on Freedem-E-SDK fails with "unknown CSR `mtvt'"

You have to use a SiFive toolchain, because freedom-e-sdk requires support for the proposed CLIC extension, which is only supported in SiFive toolchains currently, because it is still a proposal. mtvt is one of the CSRs added by the CLIC extension.

CLIC support is needed even if you are building for a target that doesn’t support the CLIC extension. There is an open issue for that problem, reported against freedom-metal I think.

You can download binaies from our web site. Or you can check out our github.com/sifive/freedom-tools repo and use that to build a compiler.