Renesas SH7781 - Manual (Page 131)

5. Exception Handling
Rev.1.00 Jan. 10, 2008 Page 101 of 1658
REJ09B0261-0100
5.5.3 Exception Requests and BL Bit
When the BL bit in SR is 0, general exceptions and interrupts are accepted.
When the BL bit in SR is 1 and an general exception other than a user break is generated, the
CPU's internal registers and the registers of the other modules are set to their states following a
manual reset, and the CPU branches to the same address as in a reset (H'A0000000). For the
operation in the event of a user break, see section 29, User Break Controller (UBC). If an ordinary
interrupt occurs, the interrupt request is held pending and is accepted after the BL bit 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. For further details, refer to the hardware
manual of the product.
Thus, normally, SPC and SSR are saved and then the BL bit in SR is cleared to 0, to enable
multiple exception state acceptance.
5.5.4 Return from Exception Handling
The RTE instruction is used to return from exception handling. When the RTE instruction is
executed, the SPC contents are restored to PC and the SSR contents to SR, and the CPU returns
from the exception handling routine by branching to the SPC address. If SPC and SSR were saved
to external memory, set the BL bit in SR to 1 before restoring the SPC and SSR contents and
issuing the RTE instruction.