C_SW1
clear_c0_cause(smp_processor_id() ? C_SW1 : C_SW0);
set_c0_cause(cpu ? C_SW1 : C_SW0);
clear_c0_cause(cpu ? C_SW1 : C_SW0);
clear_c0_cause(CAUSEF_IV | C_SW0 | C_SW1);
reserved = (C_SW0 | C_SW1) >> __ffs(C_SW0);