SH7672 datasheet(156/1292 Pages) RENESAS

156 / 1292 page

Section 5 Exception Handling

Rev. 1.00 Nov. 14, 2007 Page 130 of 1262

REJ09B0437-0100

5.9

Usage Notes

5.9.1

Value of Stack Pointer (SP)

The value of the stack pointer must always be a multiple of four. If it is not, an address error will

occur when the stack is accessed during exception handling.

5.9.2

Value of Vector Base Register (VBR)

The value of the vector base register must always be a multiple of four. If it is not, an address error

will occur when the stack is accessed during exception handling.

5.9.3

Address Errors Caused by Stacking of Address Error Exception Handling

When the stack pointer is not a multiple of four, an address error will occur during stacking of the

exception handling (interrupts, etc.) and address error exception handling will start up as soon as

the first exception handling is ended. Address errors will then also occur in the stacking for this

address error exception handling. To ensure that address error exception handling does not go into

an endless loop, no address errors are accepted at that point. This allows program control to be

shifted to the address error exception service routine and enables error processing.

When an address error occurs during exception handling stacking, the stacking bus cycle (write) is

executed. During stacking of the status register (SR) and program counter (PC), the SP is

decremented by 4 for both, so the value of SP will not be a multiple of four after the stacking

either. The address value output during stacking is the SP value, so the address where the error

occurred is itself output. This means the write data stacked will be undefined.

SH7672 Datasheet(PDF) 156 Page - Renesas Technology Corp