[yuumei]

Agreed, the best I have found so far is the SiFive Unmatched: https://www.sifive.com/boards/hifive-unmatched which is a full mini-itx motherboard. It's not a SoC though.

As far as I can see, the only thing that isn't documented is the DDR startup/training code, which is a binary blob in u-boot. There are a few registers that are undocumented which need to be set to start up but I think the rest is well documented.

[swetland]

SiFive has pretty good documentation for their cores and chips -- they are more PC/Server class (some lowspeed peripherals plus PCIE and Ethernet) than SoC style. The databook does not have register level docs for PCIE and Ethernet but both look like off-the-shelf IP (hopefully documented somewhere -- I haven't investigated) but otherwise seems pretty thorough.

https://www.sifive.com/documentation

In addition to a documented RV64 SoC, it'd be cool to see some RV32 MCUs that are a little beefier -- more competitive with the mid-range Cortex M4 and M7 stuff (more peripherals, more SRAM, etc) -- instead of the existing stuff that looks similar to very tiny M0/M3 devices.