SH7764 Datasheet, PDF (105/1752 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC Engine Family SH-4A Series

Section 2 Programming Model
2.7 Usage Notes
2.7.1 Notes on Self-Modifying Code
To accelerate the processing speed, the instruction prefetching capability of the SH-4A has been
significantly enhanced from that of the SH-4. Therefore, in the case when a code in memory is
rewritten and attempted to be executed immediately, there is increased possibility that the code
before being modified, which has already been prefetched, is executed.
To ensure execution of the modified code, one of the following sequence of instructions should be
executed between the code rewriting instruction and execution of the modified code.
(1) When the Codes to be Modified are in Non-Cacheable Area
SYNCO
ICBI @Rn
The target for the ICBI instruction can be any address within the range where no address error
exception occurs.
(2) When the Codes to be Modified are in Cacheable Area (Write-Through)
SYNCO
ICBI @Rn
All instruction cache areas corresponding to the modified codes should be invalidated by the ICBI
instruction. The ICBI instruction should be issued to each cache line. One cache line is 32 bytes.
(3) When the Codes to be Modified are in Cacheable Area (Copy-Back)
OCBP @Rm or OCBWB @Rm
SYNCO
ICBI @Rn
All operand cache areas corresponding to the modified codes should be written back to the main
memory by the OCBP or OCBWB instruction. Then all instruction cache areas corresponding to
the modified codes should be invalidated by the ICBI instruction. The OCBP, OCBWB, and ICBI
instruction should be issued to each cache line. One cache line is 32 bytes.
Note: Self-modifying code is the processing which executes instructions while dynamically
rewriting the codes in memory.
Rev. 1.00 Nov. 22, 2007 Page 49 of 1692
REJ09B0360-0100