https://git.libre-soc.org/?p=soc.git;a=blob;f=src/soc/decoder/power_decoder2.py;h=5df3f16c7c4d82e83cacea65b17d86b47814e046;hb=cecedc22c465c78f32b6a801a262b190f7109059#l930 setting SRR0/1 a 2nd time probably mot needed, must check xer_in and out need their own classes for clarity