> A developer board with a RISC-V chip and a GPU went on sale, but sold out quickly
I'd pick the quad core HF105-000 with 16GiB of RAM on Mouser for €591.50 by SiFive which is expected to ship on the 11th of February (They even have a datasheet for the SiFive HiFive Unmatched). And for it you plug your GPU card into the PCIe Gen3 x8 slot, which in my mind is a better option.
Biting the hand that feeds IT
