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3.9 EIT (Exception, Interruption, and Trap)
EIT indicates suspension of program execution due to generation of an event while
executing the current and other programs. It is a general term for Exception, Interrupt,
and Trap.
■ EIT (Exception, Interruption, and Trap)
The exception is an incident which occurs in relation to the context under execution. Execution restarts
from the instruction that caused the exception.
The interruption is an incident which occurs without any relation to the context under execution. The event
factor is hardware.
The trap is an incident which occurs in relation to the context under execution. There is something directed
by the program like the system call. Execution restarts from the instruction following the one that caused
the trap.
■ EIT Factor
The EIT factors are as follow.
• Reset
• User interruption (internal resource and external interruption)
•NMI
• Delayed interrupt
• Undefined instruction exception
• Trap instruction (INT)
• Trap instruction (INTE)
• Step trace trap
• Coprocessor absent trap
• Coprocessor error trap
■ Return from EIT
Use the RETI instruction to return from EIT.