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3.4.5
Hardware Interrupt Processing Time
The time period starting from generation of a hardware interrupt request until the
execution of interrupt handling routine requires the time until the instruction currently
being executed is completed plus the interrupt processing time.
■
Hardware interrupt processing time
The time period starting from generation of a hardware interrupt request and acceptance of the
interrupt until the execution of interrupt handling routine requires the interrupt request sample
waiting time and interrupt handling time (time required for preparing interrupt processing).
Figure 3.4-6 illustrates the interrupt processing time.
CPU operation
Interrupt waiting time
Interrupt request generated
: Last cycle of the instruction. The interrupt request is sampled in this part.
*
: One machine cycle corresponds with one clock interval of the machine
❍ Interrupt request sample waiting time
Refers to a time period starting after an interrupt request is generated until the instruction
currently being executed is completed. Sampling is performed in the last cycle of each
instruction to determine whether an interrupt request is generated or not. Thus, during execution
of each instruction, the CPU is unable to recognize an interrupt request, resulting in a waiting
time.
The interrupt request sample waiting time reaches the maximum value if an interrupt request
occurs immediately after the start of PCPW, RW0, ... RW7 instructions (45 machine cycles),
which have the longest execution cycle.
Figure 3.4-6 Interrupt processing time
Normal instruction
execution
Interrupt request
sample waiting time
φ
clock interval (
).
Interrupt handling
Interrupt handling time
θ
(
machine cycle)*
CHAPTER 3 INTERRUPT
Interrupt processing
routine
63
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