The HiFive Unleashed board by SiGive is pricey but it comes with 8 GB RAM *with* ECC. According to the FOSDEM talk t has no microcode.
https://www.crowdsupply.com/sifive/hifive-unleashed
https://fosdem.org/2018/schedule/event/riscv/
https://fosdem.org/2018/schedule/event/riscv/attachments/slides/2322/export/events/attachments/riscv/slides/2322/SiFive_RISC_V_FOSDEM_2018.pdf