Whilst developing for the Renesas H8S using the supplied compiler, issues were found with floating point support and code generation. I successfully built the GNU C compiler, floating point library and utilities for the H8S for the windows platform. I provided patches to the compiler maintainers for H8S features which were accepted. My compiler was available on the internet and was widely used by H8S developers.
I created the io.h files by extracting the register and bit definitions from the datasheet, then using a script convert to valid C. Custom start up code to allow system upgrades, and non volatile configuration was written by me in assembler.