Post Codes

The Xbox 360 uses Post Codes to report the current step of the boot process. They can be read using 8 post points on the bottom of the motherboard which form a hex byte.

Post Codes List

The "Possible Cause" indicates possible reasons for post code if the unit is displaying an error code on the front panel or hanging on boot.

1BL

Not applicable to Waternoose DD1, Shiva, or when Secure ROM is not used.

Hex	Name	Description	Possible Cause
0x10	BEGIN	1BL entry point
0x11	FSB_CONFIG_PHY_CONTROL	FSB function 1	FSB fail
0x12	FSB_CONFIG_RX_STATE	FSB function 2	FSB fail
0x13	FSB_CONFIG_TX_STATE	FSB function 3	FSB fail
0x14	FSB_CONFIG_TX_CREDITS	FSB function 4	FSB fail
0x15	FETCH_OFFSET	Fetch 2BL offset in flash	GPU, SB, Nand
0x16	FETCH_HEADER	Fetch 2BL header from flash
0x17	VERIFY_HEADER	Verify 2BL header	Bad 2BL header
0x18	FETCH_CONTENTS	Copy 2BL to SRAM	Bad nand image
0x19	HMACSHA_COMPUTE	Generate 2BL hash
0x1A	RC4_INITIALIZE	Initialize 2BL RC4 decryption key
0x1B	RC4_DECRYPT	Decrypt 2BL with RC4	Bad nand image
0x1C	SHA_COMPUTE	Generate 2BL hash
0x1D	SIG_VERIFY	Verify 2BL hash	Bad 2BL signature
0x1E	BRANCH	Branch to 2BL

2BL

Later retail systems uses a split 2BL which added the CB_A and renamed the CB to CB_B. Earlier units and developer systems use a single 2BL.

CB_A

Hex	Name	Description	Possible Cause
0xD0	BEGIN	CB_A entry point
0xD1	READ_FUSES	Read eFUSEs
0xD2	VERIFY_OFFSET_CB_B	Verify CB_B offset in flash	Bad nand image
0xD3	FETCH_HEADER_CB_B	Fetch CB_B header from flash
0xD4	VERIFY_HEADER_CB_B	Verify CB_B header	Bad CB_B header
0xD5	FETCH_CONTENTS_CB_B	Copy CB_B to SRAM	Bad nand image
0xD6	HMACSHA_COMPUTE_CB_B	Generate CB_B hash
0xD7	RC4_INTIALIZE_CB_B	Initialize CB_B RC4 decryption key
0xD8	RC4_DECRYPT_CB_B	Decrypt CB_B with RC4	Bad nand image
0xD9	SHA_COMPUTE_CB_B	Generate CB_B hash
0xDA	SHA_VERIFY_CB_B	Verify CB_B hash	Bad CB_B signature
0xDB	BRANCH_CB_B	Branch to CB_B

---

1BL Panics

Hex	Name	Description	Possible Cause
0x81	MACHINECHECK	Panic - Machine Check
0x82	DATA_STORAGE	Panic - Data Storage
0x83	DATA_SEGMENT	Panic - Data Segment
0x84	INSTRUCTION_STORAGE	Panic - Instruction Storage
0x85	INSTRUCTION_SEGMENT	Panic - Instruction Segment
0x86	EXTERNAL	Panic - External	CPU interrupt triggered
0x87	ALIGNMENT	Panic - Alignment
0x88	PROGRAM	Panic - Program	Illegal instruction
0x89	FPU_UNAVAILABLE	Panic - FPU Unavailable
0x8A	DECREMENTER	Panic - Decrementer
0x8B	HYPERVISOR_DECREMENTER	Panic - Hypervisor Decrementer
0x8C	SYSTEM_CALL	Panic - System Call
0x8D	TRACE	Panic - Trace
0x8E	VPU_UNAVAILABLE	Panic - VPU Unavailable
0x8F	MAINTENANCE	Panic - Maintenance
0x90	VMX_ASSIST	Panic - VMX Assist
0x91	THERMAL_MANAGEMENT	Panic - Thermal Management
0x92	WRONG_THREAD	Panic - Wrong Thread	1BL executed on wrong thread
0x93	TOO_MANY_CORES	Panic - Too Many Cores	1BL executer on wrong core
0x94	VERIFY_OFFSET	Panic - Verify Offset	Bad 2BL offset
0x95	VERIFY_HEADER	Panic - Verify Header	Bad 2BL header
0x96	SIG_VERIFY	Panic - Signature Verify	Bad 2BL signature
0x97	NONHOST_RESUME_STATUS	Panic - Non Host Resume Status
0x98	NEXT_STAGE_SIZE	Panic - Next Stage Size	2BL size too large

---

2BL

Later retail systems uses a split 2BL which added the CB_A and renamed the CB to CB_B. Earlier units and developer systems use a single 2BL.

CB_A

Hex	Name	Description	Possible Cause
0xF0	VERIFY_OFFSET_CB_B	Panic - Verify Offset	Bad CB_B offset
0xF1	VERIFY_HEADER_CB_B	Panic - Verify Header	Bad CB_B header
0xF2	SHA_VERIFY_CB_B	Panic - Signature Verify	Bad CB_B signature
0xF3	ENTRY_SIZE_INVALID_CB_B	Panic - Entry Size Invalid	CB_B size too large

---