SH7261 datasheet(142/1348 Pages) RENESAS

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Section 5 Exception Handling

Rev. 2.00 Sep. 07, 2007 Page 110 of 1312

REJ09B0320-0200

5.6.3

Interrupt Exception Handling

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 level bits (I3 to I0) of the status register (SR).

When an interrupt is accepted, interrupt exception handling begins. In interrupt exception

handling, the CPU fetches the exception service routine start address which corresponds to the

accepted interrupt from the exception handling vector table, and saves SR and the program counter

(PC) to the stack. In the case of interrupt exception handling other than the NMI or user break,

with usage of the register banks enabled, general registers R0 to R14, control register GBR,

system registers MACH, MACL, and PR, and the vector number of the interrupt exception

handling to be executed are saved in the register banks. In the case of exception handling due to an

address error, bus error, NMI interrupt, user break interrupt, or instruction, saving is not performed

to the register banks. If saving has been performed to all register banks (0 to 14), automatic saving

to the stack is performed instead of register bank saving. In this case, an interrupt controller setting

must have been made so that register bank overflow exceptions are not accepted (the BOVE bit in

IBNR of the INTC is 0). If the interrupt controller is set to accept register bank overflow

exceptions (the BOVE bit in IBNR of INTC is set to 1), a register bank overflow exception will

occur. Next, the priority level value of the accepted interrupt is written to the I3 to I0 bits in SR.

For NMI, however, the priority level is 16, but the value set in the I3 to I0 bits is H'F (level 15).

Then, after jumping to the start address of the interrupt exception service routine fetched from the

exception handling vector table, program execution starts. The jump that occurs is not a delayed

branch. See section 6.6, Operation, for further details of interrupt exception handling.

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