Symptom:
ROMMON get_mac_addr and IOSXE IDPROM access fail on booting standby RP2. This can manifest itself in a few ways:

- Repeated kernel panic and reload on standby RP2. This will produce cores in the harddisk:/core directory on the standby.

- Midplane IDPROM errors & failure of the cman service on the standby RP2.

%IOSXEBOOT-4-BOOT_SRC: (rp/0): Non-HD Boot
11/12 18:04:36.057: %CMRP-3-IDPROM_ACCESS: Failed to access or process IDPROM 'midplane': Device or resource busy -Traceback= 1#ddd6f7e3399c90f9130aacffb3dad1e5   errmsg:F6DC2000+F24 :8048000+2F608 :8048000+509D8 :8048000+3D910 :8048000+3EEBF c:F69E9000+16670 :8048000+12F91 
 
Nov 12 18:04:37.678 R0/0: %BOOT-0-APP_STARTFAILCRIT: Failed to launch a critical process cman

Conditions:
This issue occurs when the active RP2 holds an exclusive lock on the chassis midplane. During normal operation, this lock should be held only momentarily (during a hardware access) and then released immediately.

The presence of an external USB device can trigger an interrupt race condition that leads to this lock getting stuck.