Service manual

Troubleshooting 3-85
Initially on power-up or reset each microprocessor on the CSB runs a fail-safe
loader image and the microprocessor is said to be in fail-safe loader mode (FSL
mode). This FSL image resides in flash ROM in a different location than the
normal firmware image run in the microprocessor.
The FSL image has two functions:
• it runs a checksum test on the primary firmware run by the microprocessor.
• it loads a new firmware image into its associated flash ROM when
instructed to do so by the SCM update command only.
If the checksum test passes, the FSL code jumps to the normal firmware image
and the microprocessor runs that code. If the checksum test fails, the
microprocessor remains in FSL mode and the resource, whatever it is, is not
configured into the system. Appropriate error messages are sent to the console
if a checksum failure occurs and the corrupt image can be replaced. Only the
SCM update command can be used to load healthy firmware into a micro’s
flash EEPROM when the micro is in FSL mode. See Appendix D for
instructions on running the SCM update command.
If the checksum test passes and the normal firmware image still does not run on
the microprocessor, FSL mode can be forced by installing a jumper on the failing
module or backplane. See Table 3–13.