Table of Contents
Advertisement
3.8
EIT (Exception, Interrupt, and Trap)
EIT indicates that a program being executed is suspended by an event for the purpose
of executing another program. EIT is the generic name for exception, interrupt, and
trap.
I Notes on EIT
❍ Exception
An exception is an event that is thrown in accordance with the context of program execution.
Execution resumes later, starting at the instruction that caused the exception.
❍ Interrupt
An interrupt is an event that is thrown by hardware with no relationship to the context of the
program execution.
❍ Trap
A trap is an event that is thrown in accordance with the context of the program execution. As
with system calls, some traps are instructed by the program. Execution resumes, beginning
from the instruction following the instruction that caused the trap.
I EIT sources
The EIT sources are as follows:
•
Reset
•
User interrupt (internal source, external interrupt)
•
Delayed interrupt
•
Undefined instruction exception
•
Trap instruction (INT)
•
Trap instruction (INTE)
•
Step trace trap
•
Coprocessor absence trap
•
Coprocessor error trap
I Return from EIT
Use the RETI instruction to return from EIT.
I Delay slot
EIT restrictions apply to the delay slots of branch instructions.
For more information, see Section 3.7.1 "Operations with Delay Slots".
CHAPTER 3 MEMORY SPACE, CPU AND CONTROL UNIT
53
Advertisement
Table of Contents
