(https://www.wch-ic.com/products/CH32V203.html). this is the CH32V203G6 which is a QFN-28 version of the chip, with 32KB of Flash and 10KB of SRAM. we would have preferred to use the F8 QFN-20 with double the flash and RAM, but this variant part was easier to buy. we wanted to get going quickly so the board layout is 4-layer.