SH7144 Datasheet, PDF (138/773 Pages) Renesas Technology Corp – Hitachi SuperH RISC engine

7.3.2 Break on On-Chip Memory Instruction Fetch Cycle
Data in on-chip memory (on-chip ROM and/or RAM) is always accessed as 32-bits data in one
bus cycle. Therefore, two instructions can be retrieved in one bus cycle when fetching instructions
from on-chip memory. At such times, only one bus cycle is generated, but it is possible to cause
independent breaks by setting the start addresses of both instructions in the user break address
register (UBAR). In other words, when wanting to effect a break using the latter of two addresses
retrieved in one bus cycle, set the start address of that instruction in UBAR. The break will occur
after execution of the former instruction.
7.3.3 Program Counter (PC) Values Saved
Break on Instruction Fetch: The program counter (PC) value saved to the stack in user break
interrupt exception processing is the address that matches the break condition. The user break
interrupt is generated before the fetched instruction is executed. If a break condition is set in an
instruction fetch cycle placed immediately after a delayed branch instruction (delay slot), or on an
instruction that follows an interrupt-disabled instruction, however, the user break interrupt is not
accepted immediately, but the break condition establishing instruction is executed. The user break
interrupt is accepted after execution of the instruction that has accepted the interrupt. In this case,
the PC value saved is the start address of the instruction that will be executed after the instruction
that has accepted the interrupt.
Break on Data Access (CPU/DTC, DMAC): The program counter (PC) value is the top address
of the next instruction after the last instruction executed before the user break exception
processing started. When data access (CPU/DTC, DMAC) is set as a break condition, the place
where the break will occur cannot be specified exactly. The break will occur at the instruction
fetched close to where the data access that is to receive the break occurs.
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