How Coreboot.rom is made?

[ali hagigat]

I have listed all the lines that mentions the symbol, "coreboot.rom" in the
top Makefile:
coreboot: $(obj)/coreboot.rom
update:
    dongle.py -c /dev/term/1 $(obj)/coreboot.rom EOF

Where is dongle.py?
How coreboot.rom is made? Where is the rule for it?