I recently acquired a Spark Fun RED-V Redboard with a FE310-G002 and have been working on some bare-metal programming with it. However, I have struggled to get the UARTs to work. I was poking through some of other peoples source code and noticed that the UART may need to be enabled through the GPIO. I see references to iof_en and iof_sel in the manual under section 17.8 HW I/O Functions (IOF). However, these registers are never mentioned anywhere else in the document. Their locations and contents are not defined in the manual as far as I can tell.
You can find info in our bsp which is found at github.com/sifive/freedom-e-sdk. See for instance
There is also driver code in there which is presumably