I'm very confused about what bit 0 of the Authentication Status (AUTHSTTS) register means: has it entered challenge mode, or does it mean the challenge value is ready? Could someone please help me understand this? Thank you so much! 
If the chip has not enabled challenge mode, will bit 0 of AUTHSTTS still be set to 1?
AUTHSTTS[CHALRDY] is a read-only status bit that indicates when the challenge is ready. The debugger should wait for CHALRDY to be asserted before reading the challenge in the KEYCHALn registers.
BR, VaneB