go doubleSpeed
wait for mode3
enable mode0 int
write 0 to cgbpal1
wait for int

on int:
jump to 0x1000
some of nops
write 1 to cgbpal1
bunch of nops
read cgbpal1
output value of cgbpal1&7

cgbpal_m3start_1.gbc should output 1
cgbpal_m3start_2.gbc should output 0