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5.7
Usage Notes
1. Return from exception handling
a. Check the BL bit in SR with software. If SPC and SSR have been saved to external
memory, set the BL bit in SR to 1 before restoring them.
b. Issue an RTE instruction. When RTE is executed, the SPC contents are set in PC, the SSR
contents are set in SR, and branch is made to the SPC address to return from the exception
handling routine.
2. If an exception or interrupt occurs when SR.BL = 1
a. Exception
When an exception other than a user break occurs, a manual reset is executed. The value in
EXPEVT at this time is H'0000 0020; the value of the SPC and SSR registers is undefined.
b. Interrupt
If an ordinary interrupt occurs, the interrupt request is held pending and is accepted after
the BL bit in SR has been cleared to 0 by software. If a nonmaskable interrupt (NMI)
occurs, it can be held pending or accepted according to the setting made by software. In the
sleep or standby state, however, an interrupt is accepted even if the BL bit in SR is set to 1.
3. SPC when an exception occurs
a. Re-execution type exception
The PC value for the instruction in which the exception occurred is set in SPC, and the
instruction is re-executed after returning from exception handling. If an exception occurs in
a delay slot instruction, however, the PC value for the delay slot instruction is saved in SPC
regardless of whether or not the preceding delay slot instruction condition is satisfied.
b. Completion type exception or interrupt
The PC value for the instruction following that in which the exception occurred is set in
SPC. If an exception occurs in a branch instruction with delay slot, however, the PC value
for the branch destination is saved in SPC.
4.
An exception must not be generated in an RTE instruction delay slot, as the operation will be
undefined in this case.
Rev. 4.0, 04/00, page 115 of 850
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