HD6417750 Datasheet, PDF (840/1039 Pages) Renesas Technology Corp – SuperH RISC engine

20.3.4 Instruction Access Cycle Break
1. When an instruction access/read/word setting is made in the break bus cycle register
(BBRA/BBRB), an instruction access cycle can be used as a break condition. In this case,
breaking before or after execution of the relevant instruction can be selected with the
PCBA/PCBB bit in the break control register (BRCR). When an instruction access cycle is
used as a break condition, clear the LSB of the break address registers (BARA, BARB) to 0. A
break will not be generated if this bit is set to 1.
2. When a pre-execution break is specified, the break is effected when it is confirmed that the
instruction is to be fetched and executed. Therefore, an overrun-fetched instruction (an
instruction that is fetched but not executed when a branch or exception occurs) cannot be used
in a break. However, if a TLB miss or TLB protection violation exception occurs at the time of
the fetch of an instruction subject to a break, the break exception handling is carried out first.
The instruction TLB exception handling is performed when the instruction is re-executed (see
section 5.4, Exception Types and Priorities). Also, since a delayed branch instruction and the
delay slot instruction are executed as a single instruction, if a pre-execution break is specified
for a delay slot instruction, the break will be effected before execution of the delayed branch
instruction. However, a pre-execution break cannot be specified for the delay slot instruction
for an RTE instruction.
3. With a pre-execution break, the instruction set as a break condition is executed, then a break
interrupt is generated before the next instruction is executed. When a post-execution break is
set for a delayed branch instruction, the delay slot is executed and the break is effected before
execution of the instruction at the branch destination (when the branch is made) or the
instruction two instructions ahead of the branch instruction (when the branch is not made).
4. When an instruction access cycle is set for channel B, break data register B (BDRB) is ignored
in judging whether there is an instruction access match. Therefore, a break condition specified
by the DBEB bit in BRCR is not executed.
Rev. 6.0, 07/02, page 788 of 986