HD6417705F133V Datasheet, PDF (129/741 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperH RISC engine Family/SH7700 Series

3.4 MMU Functions
3.4.1 MMU Hardware Management
There are two kinds of MMU hardware management as follows.
1. The MMU decodes the virtual address accessed by a process and performs address translation
by controlling the TLB in accordance with the MMUCR settings.
2. In address translation, the MMU receives page management information from the TLB, and
determines the MMU exception and whether the cache is to be accessed (using the C bit). For
details of the determination method and the hardware processing, see section 3.5, MMU
Exceptions.
3.4.2 MMU Software Management
There are three kinds of MMU software management, as follows.
1. MMU register setting
MMUCR setting, in particular, should be performed in areas P1 and P2 for which address
translation is not performed. Also, since SV and IX bit changes constitute address translation
system changes, in this case, TLB flushing should be performed by simultaneously writing 1 to
the TF bit also. Since MMU exceptions are not generated in the MMU disabled state with the
AT bit cleared to 0, use in the disabled state must be avoided with software that does not use
the MMU.
2. TLB entry recording, deletion, and reading
TLB entry recording can be done in two ways by using the LDTLB instruction, or by writing
directly to the memory-mapped TLB. For TLB entry deletion and reading, the memory
allocation TLB can be accessed. See section 3.4.3, MMU Instruction (LDTLB), for details of
the LDTLB instruction, and section 3.6, Memory-Mapped TLB, for details of the memory-
mapped TLB.
3. MMU exception processing
When an MMU exception is generated, it is handled on the basis of information set from the
hardware side. See section 3.5, MMU Exceptions, for details.
When single virtual memory mode is used, it is possible to create a state in which physical
memory access is enabled in the privileged mode only by clearing the share status bit (SH) to 0 to
specify recording of all TLB entries. This strengthens inter-process memory protection, and
enables special access levels to be created in the privileged mode only.
Recording a 1- or 4- kbyte page TLB entry may result in a synonym problem. See section 3.4.4,
Avoiding Synonym Problems.
Rev. 2.00, 09/03, page 81 of 690