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B-7
Cisco 3600 Series Routers Hardware Installation Guide
OL-2056-05
Appendix B Using the ROM Monitor
ROM Monitor Command Descriptions
Debugging Commands
Most debugging commands are functional only when Cisco IOS software has crashed or failed to
initialize (boot). Debugging commands should normally be entered only under the direction of a Cisco
engineer. If you enter a debugging command and Cisco IOS crash information is not available, the
following error message appears:
“xxx: kernel context state is invalid, cannot proceed.”
The following ROM monitor debugging commands provide information about software failures:
• stack or k—Produce a stack trace.
• context—View processor context.
• frame—View an individual stack frame.
• sysret—View return information from the last booted system image. This information includes the
reason for terminating the image, a stack dump of up to eight frames, and, if an exception is
involved, the address where the exception occurred. For example:
rommon 8> sysret
System Return Info:
count: 19, reason: a SegV exception
pc:0x802b1040, error address: 0x802b1040
Stack Trace:
FP: 0x80908398, PC: 0x802b102c
FP: 0x809083b0, PC: 0x802b0b88
FP: 0x809083d8, PC: 0x8017039c
FP: 0x809083e8, PC: 0x8016f764
Configuration Register Commands
The configuration register resides in NVRAM. You can view or modify the configuration register from
either the ROM monitor or the operating system software.
For procedures used to change the configuration register from the operating system, and for information
about configuration register settings, see Appendix C, “Configuration Register.”
To modify the configuration register from the ROM monitor, you can:
• Enter the confreg command by itself for menu mode. See the “Modifying the Configuration Register
in Menu Mode” section below.
• Enter the confreg command plus the new hexidecimal value of the configuration register. See the
“Modifying the Configuration Register by Hexidecimal Entry” section on page B-8.
In either case, the new configuration register value is written into NVRAM, but is not effective until you
reboot (using the ROM monitor reset command) or power cycle the router.