EXCCAUSE Code	Cause Name	Cause Description	Required Option2	EXCVADDR Loaded
0	IllegalInstructionCause	Illegal instruction	Exception	No
2	InstructionFetchErrorCause	Processor internal physical address or data error during instruction fetch	Exception	Yes
3	LoadStoreErrorCause	Processor internal physical address or data error during load or store	Exception	Yes
4	Level1InterruptCause	Level-1 interrupt as indicated by set level-1 bits in the INTERRUPT register	Interrupt	No
61	IntegerDivideByZeroCause	QUOS, QUOU, REMS, or REMU divisor operand is zero	32-bit Integer Divide	No
9	LoadStoreAlignmentCause	Load or store to an unaligned address	Unaligned Exception	Yes
20	InstFetchProhibitedCause	An instruction fetch referenced a page mapped with an attribute that does not permit instruction fetch	Region Protection or MMU	Yes
28	LoadProhibitedCause	A load referenced a page mapped with an attribute that does not permit loads	Region Protection or MMU	Yes
29	StoreProhibitedCause	A store referenced a page mapped with an attribute that does not permit	Region Protection or MMU	Yes

¹ No hardware support for this exception; however, the software-detected event is reported as "exccause 6" at Postmortem. After reboot, ESP.getResetInfo() will report the event as "exccause 0".

² Identifies Xtensa config option for the silicon. The question that needs answering is which of these was included in the ESP8266 silicon?

EXCCAUSE Code	Cause Name	Cause Description	Required Option2	EXCVADDR Loaded
1	SyscallCause	SYSCALL instruction	Exception	No
5	AllocaCause	MOVSP instruction, if caller’s registers are not in the register file	Windowed Register	No
7	Reserved for Tensilica
8	PrivilegedCause	Attempt to execute a privileged operation when CRING != 0	MMU	No
10..11	Reserved for Tensilica
12	InstrPIFDateErrorCause	PIF data error during instruction fetch	Processor Interface	Yes
13	LoadStorePIFDataErrorCause	Synchronous PIF data error during LoadStore access	Processor Interface	Yes
14	InstrPIFAddrErrorCause	PIF address error during instruction fetch	Processor Interface	Yes
15	LoadStorePIFAddrErrorCause	Synchronous PIF address error during LoadStore access	Processor Interface	Yes
16	InstTLBMissCause	Error during Instruction TLB refill	MMU	Yes
17	InstTLBMultiHitCause	Multiple instruction TLB entries matched	MMU	Yes
18	InstFetchPrivilegeCause	An instruction fetch referenced a virtual address at a ring level less than CRING	MMU	Yes
19	Reserved for Tensilica
21..23	Reserved for Tensilica
24	LoadStoreTLBMissCause	Error during TLB refill for a load or store	MMU	Yes
25	LoadStoreTLBMultiHitCause	Multiple TLB entries matched for a load or store	MMU	Yes
26	LoadStorePrivilegeCause	A load or store referenced a virtual address at a ring level less than CRING	MMU	Yes
27	Reserved for Tensilica
30..31	Reserved for Tensilica
32..39	CoprocessornDisabled	Coprocessor n instruction when cpn disabled. n varies 0..7 as the cause varies 32..39	Coprocessor	No
40..63	Reserved

Info from Xtensa Instruction Set Architecture (ISA) Reference Manual