Eit (Exception, Interrupt, And Trap) - Fujitsu FR60 Hardware Manual

3.10 EIT (Exception, Interrupt, and Trap)

EIT, a generic term for exception, interrupt, and trap, refers to suspending program
execution if an event occurs during execution and then executing another program.
■ EIT (Exception, Interrupt, and Trap)
An exception is an event that occurs related to the execution context. Execution restarts from
the instruction that caused the exception.
An interrupt is an event that occurs independently of execution context. The event is caused by
hardware.
A trap is an event that occurs related to the execution context. Some traps, such as system
calls, are specified in a program. Execution restarts from the instruction following the one that
caused the trap.
■ Features
• Multiple interrupt is supported to the interruption.
• It is a level mask function (15 levels are available the user) to the interruption.
• Trap instruction (INT)
• EIT (hardware/software) for emulator startup
■ EIT Causes
The following are causes of EIT:
• Reset
• User interrupt (internal resource, external interrupt)
• NMI
• Delayed interrupt
• Undefined instruction exception
• Trap instruction (INT)
• Trap instruction (INTE)
• Step trace trap
• No-coprocessor trap
• Coprocessor error trap
■ Return from EIT
Use the RETI instruction to return from EIT.
CHAPTER 3 CPU AND CONTROL UNITS
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