+;* bootROM, a very small bootloader for $NAME
+;*
+;* protocol details:
+;* abbrv: H = Host, CPU = C
+;*
+;* value/cmd | direction | comment
+;* ------------------------------------------------------------
+;* 'H' | H -> C | enter bootROM ("HI")
+;* 'O' | C -> H | ack bootROM entry ("OH HAI")
+;*
+;* 'W'0xZZZZZZZZ0xYYYYYYYY| H -> C | write instr (0xYY...Y) to
+;* | address (0xZZ...Z)
+;* 'D' | C -> H | instr write done
+;*
+;* 'R'0xZZZZZZZZ | H -> C | read instr from address (0xZZ..Z)
+;* 'F'0xYYYYYYYY | C -> H | instr read done and return instr
+;*
+;* 'Q'0xZZZZZZZZ0xYYYYYYYY| H -> C | write data (0xYY...Y) to
+;* | address (0xZZ...Z)
+;* 'A' | C -> H | data write done
+;*
+;* 'T'0xZZZZZZZZ | H -> C | read data from address (0xZZ..Z)
+;* 'G'0xYYYYYYYY | C -> H | read done and return data
+;*
+;* 'J'0xZZZZZZZZ | H -> C | jump to address (0xZZ...Z)
+;*/