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CHAPTER 3 MEMORY SPACE, CPU AND CONTROL UNIT
3.8.4
Multiple EIT Processing
If two or more EIT sources occur at the same time, the CPU selects and accepts one
EIT source. After executing the EIT sequence, the CPU repeats monitoring for EIT
sources.
If no acceptable EIT source can be found at EIT source detection, the CPU executes
the instruction of the handler for the EIT source it accepted last.
Therefore, if two or more EIT sources occur at the same time, the handler execution
order of the sources depends on the following two elements:
• EIT source acceptance priority
• How other sources were masked when the source was accepted
I EIT source acceptance priority
EIT source acceptance priority means the order in which a source for EIT sequence execution is
selected after the PS and PC are saved, the PC updated as necessary, and other sources
masked. The handler of the source previously accepted is not always executed first.
Table 3.8-3 "EIT source acceptance priority and masking of other sources" shows the EIT
source acceptance priority.
Table 3.8-3 EIT source acceptance priority and masking of other sources
Acceptance
priority
Table 3.8-4 "EIT handler execution order" shows the execution order of the handlers for the
concurrent EIT sources, considering the mask processing for other EIT sources after an EIT
source is accepted.
58
1
Reset
2
Undefined instruction exception
INT instruction
3
Coprocessor absence trap
Coprocessor error trap
4
User interrupt
5
(NMI)
7
INTE instruction
8
Step trace trap
Source
Other sources are discarded.
Canceled
I flag = 0
None
ILM = level of the accepted source
ILM=15
ILM=4
ILM=4
Masking for other sources
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