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CHAPTER 3 CPU
3.5.17
Time Required to Start Interrupt Processing
The time for terminating the currently executing instruction plus the interrupt handling
time is required from generation of the hardware interrupt request to execution of the
interrupt-processing.
I Time Required to Start Interrupt Processing
The interrupt request sampling wait time and the interrupt handling time (time required for preparation for
interrupt processing) are required from generation of the interrupt request and acceptance of interrupt, to
execution of the interrupt processing. Figure 3.5-17 shows the interrupt processing time.
Operation of CPU
Interrupt waiting time
: Instruction last cycle, sampling interrupt request here
: One machine cycle is equal to one clock cycle of the machine clock 0lligent I/O Service ( ).
G
Interrupt request sampling wait time
It indicates a time from the generation of the interrupt request to the termination of the currently executing
instruction.
Whether the interrupt request is generated or not is determined by sampling the interrupt request in the last
cycle of each instruction. The CPU cannot recognize the interrupt request during execution of each
instruction, as a result wait time occurs.
Reference:
The interrupt request sampling wait time is longest when the interrupt request is generated
immediately after starting execution of the POPW, RW0,... RW7 instructions with the longest
execution cycle (45 machine cycles).
G
Interrupt handling time (θ machine cycles)
The CPU requires an interrupt handling time of θ machine cycles to save the dedicated registers to the
system stack and fetch the interrupt vector table address after accepting the interrupt request. The interrupt
handling time (θ) is obtained using the following equations.
θ = 24 + 6 x Z machine cycles (Z: compensation value of interrupt handling time)
The interrupt handling time depends on the address set by the stack pointer. Table 3.5-13 shows the
compensation value (Z) of the interrupt handling time.
90
Figure 3.5-17 Interrupt Processing Time
Normal onsstruction execution
Interrupt request
sampling waiting time
Interrupt request generate
Interrupt handling
Interrupt processing
Interrupt handling time
( machinecycle)*
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