SH7018 datasheet(70/431 Pages) RENESAS

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Table 5.8

Interrupt Priority Order

Type

Priority Level

Comment

NMI

Fixed priority level. Cannot be masked.

IRQ

0 to 15

Set with interrupt priority level setting registers A

through H (IPRA to IPRH).

On-chip peripheral module

0 to 15

Set with interrupt priority level setting registers A

through H (IPRA to IPRH).

5.4.2

Interrupt Exception Processing

When an interrupt occurs, its priority level is ascertained by the interrupt controller (INTC). NMI

is always accepted, but other interrupts are only accepted if they have a priority level higher than

the priority level set in the interrupt mask bits (I3 to I0) of the status register (SR).

When an interrupt is accepted, exception processing begins. In interrupt exception processing, the

CPU saves SR and the program counter (PC) to the stack. The priority level value of the accepted

interrupt is written to SR bits I3 to I0. For NMI, however, the priority level is 16, but the value set

in I3 to I0 is H'F (level 15). Next, the start address of the exception service routine is fetched from

the exception processing vector table for the accepted interrupt, that address is jumped to and

execution begins. See section 6.4, Interrupt Operation, for more information on the interrupt

exception processing.

5.5

Exceptions Triggered by Instructions

Exception processing can be triggered by trap instructions, general illegal instructions, and illegal

slot instructions, as shown in table 5.9.

Table 5.9

Types of Exceptions Triggered by Instructions

Type

Source Instruction

Comment

Trap instructions

TRAPA

—

Illegal slot

instructions

Undefined code placed

immediately after a delayed

branch instruction (delay slot)

and instructions that rewrite the

Delayed branch instructions: JMP, JSR,

BRA, BSR, RTS, RTE, BF/S, BT/S, BSRF,

BRAF

Instructions that rewrite the PC: JMP, JSR,

BRA, BSR, RTS, RTE, BT, BF, TRAPA,

BF/S, BT/S, BSRF, BRAF

General illegal

instructions

Undefined code anywhere

besides in a delay slot

—

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