Nortel DMS 100 Series Maintenance Manual page 71

Exception services includes the following activities:
• trap administration
• trap reporting
• trap data access and display
Exceptions
An exception is a special condition at the ROM or TASK level that preempts
normal processing. Both internal and external conditions can cause
exceptions.
Internal conditions that cause an exception are:
• not permitted instructions
• address errors
• tracing
• breakpoints
• coprocessor protocol violations
The following are external conditions that cause an exception:
• interrupts from external devices
• bus errors
• coprocessor-detected errors
• resets
ROM-level exception processing
On initialization, the firmware maps all vectors to local exception handlers to
provide:
• the least possible error recording and reporting
• establishment of a bootstrap environment
• debugging of utilities
• hardware abstraction
TASK-level exception processing
The TASK-level exception-processing reports critical information on
hardware and software states. The TASK-level reports critical information if
a hardware or software fault prevents normal operation of the XPM unit. The
process restores the task to a known point of execution and allows the task to
perform recovery actions. If recovery is not possible, the TASK-level
exception processing initiates local maintenance to start or set the XPM unit
again.
DMS-100 Family Remote Switching Center Multi-Access Maintenance Manual XPM11 and up
Maintenance overview 2-55