SH7018 Datasheet, PDF (64/431 Pages) Renesas Technology Corp – SuperH™ RISC engine

5.1.2 Exception Processing Operations
The exception processing sources are detected and begin processing according to the timing
shown in table 5.2.
Table 5.2 Timing of Exception Source Detection and the Start of Exception Processing
Exception Source
Power-on reset
Address error
Interrupts
Instructions
Trap instruction
General illegal
instructions
Illegal slot
instructions
Timing of Source Detection and Start of Processing
Starts when the RES pin changes from low to high.
Detected when instruction is decoded and starts when the
previous executing instruction finishes executing.
Detected when instruction is decoded and starts when the
previous executing instruction finishes executing.
Starts from the execution of a TRAPA instruction.
Starts from the decoding of undefined code anytime except after
a delayed branch instruction (delay slot).
Starts from the decoding of undefined code placed in a delayed
branch instruction (delay slot) or of instructions that rewrite the
PC.
When exception processing starts, the CPU operates as follows:
1. Exception processing triggered by reset:
The initial values of the program counter (PC) and stack pointer (SP) are fetched from the
exception processing vector table (PC and SP are respectively the H'00000000 and
H'00000004 addresses). See section 5.1.3, Exception Processing Vector Table, for more
information. 0 is then written to the vector base register (VBR) and 1111 is written to the
interrupt mask bits (I3 to I0) of the status register (SR). The program begins running from the
PC address fetched from the exception processing vector table.
2. Exception processing triggered by address errors, interrupts and instructions:
SR and PC are saved to the stack indicated by R15. For interrupt exception processing, the
interrupt priority level is written to the SR’s interrupt mask bits (I3 to I0). For address error
and instruction exception processing, the I3 to I0 bits are not affected. The start address is then
fetched from the exception processing vector table and the program begins running from that
address.
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