Hi Stanley,
The two flag bits GF0 and GF1 can be used to indicate whether an interrupt occurred during normal operation or during an Idle. When you activate the Idle mode just set one (or both) of the flag bits just before you set the Idle mode. When Idle is terminated by an interrupt, the interrupt service routine (ISR) can examine the flag bits.
This is handy to know while the processor is asleep so that when it wakes up it will know what happened.
Regards,
Charles Bannister