Renesas RL78/G1P Hardware User Manual page 606

RL78/G1P
15.4.2 Software interrupt request acknowledgment
A software interrupt request is acknowledged by BRK instruction execution. Software interrupts cannot be disabled.
If a software interrupt request is acknowledged, the contents are saved into the stacks in the order of the program
status word (PSW), then program counter (PC), the IE flag is reset (0), and the contents of the vector table (0007EH,
0007FH) are loaded into the PC and branched.
Restoring from a software interrupt is possible by using the RETB instruction.
Caution Can not use the RETI instruction for restoring from the software interrupt.
15.4.3 Multiple interrupt servicing
Multiple interrupt servicing occurs when another interrupt request is acknowledged during execution of an interrupt.
Multiple interrupt servicing does not occur unless the interrupt request acknowledgment enabled state is selected (IE =
1). When an interrupt request is acknowledged, interrupt request acknowledgment becomes disabled (IE = 0). Therefore,
to enable multiple interrupt servicing, it is necessary to set (1) the IE flag with the EI instruction during interrupt servicing to
enable interrupt acknowledgment.
Moreover, even if interrupts are enabled, multiple interrupt servicing may not be enabled, this being subject to interrupt
priority control. Two types of priority control are available: default priority control and programmable priority control.
Programmable priority control is used for multiple interrupt servicing.
In the interrupt enabled state, if an interrupt request with a priority higher than that of the interrupt currently being
serviced is generated, it is acknowledged for multiple interrupt servicing. If an interrupt with a priority equal to or lower
than that of the interrupt currently being serviced is generated during interrupt servicing, it is not acknowledged for multiple
interrupt servicing. Interrupt requests that are not enabled because interrupts are in the interrupt disabled state or
because they have a lower priority are held pending. When servicing of the current interrupt ends, the pending interrupt
request is acknowledged following execution of at least one main processing instruction execution.
Table 15-5 shows relationship between interrupt requests enabled for multiple interrupt servicing and Figure 15-10
shows multiple interrupt servicing examples.
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CHAPTER 15 INTERRUPT FUNCTIONS
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