Renesas SH7781 - Manual (Page 220)

7. Memory Management Unit (MMU)
Rev.1.00 Jan. 10, 2008 Page 190 of 1658
REJ09B0261-0100
7.7 Memory-Mapped TLB Configuration
To enable the ITLB and UTLB to be managed by software, their contents are allowed to be read
from and written to by a program in the P1/P2 area with a MOV instruction in privileged mode.
Operation is not guaranteed if access is made from a program in another area.
After the memory-mapped TLB has been accessed, execute one of the following three methods
before an access (including an instruction fetch) to an area other than the P1/P2 area is performed.
1. Execute a branch using the RTE instruction. In this case, the branch destination may be an area
other than the P1/P2 area.
2. Execute the ICBI instruction for any address (including non-cacheable area).
3. If the MT bit in IRMCR is 0 (initial value) before accessing the memory-mapped TLB, the
specific instruction does not need to be executed. However, note that the CPU processing
performance will be lowered because the instruction fetch is performed again for the next
instruction after MMUCR has been updated.
Note that the method 3 may not be guaranteed in the future SuperH Series. Therefore, it is
recommended that the method 1 or 2 should be used for being compatible with the future SuperH
Series.
The ITLB and UTLB are allocated to the P4 area in the virtual address space.
In TLB compatible mode, VPN, V, and ASID in the ITLB can be accessed as an address array,
PPN, V, SZ, PR, C, and SH as a data array. VPN, D, V, and ASID in the UTLB can be accessed as
an address array, PPN, V, SZ, PR, C, D, WT, and SH as a data array. V and D can be accessed
from both the address array side and the data array side.
In TLB extended mode, VPN, V, and ASID in the ITLB can be accessed as an address array, PPN,
V, ESZ, EPR, C, and SH as a data array. VPN, D, V, and ASID in the UTLB can be accessed as
an address array, PPN, V, ESZ, EPR, C, D, WT, and SH as a data array. V and D can be accessed
from both the address array side and the data array side.
In both TLB compatible mode and TLB extended mode, only longword access is possible.
Instruction fetches cannot be performed in these areas. For reserved bits, a write value of 0 should
be specified; their read value is undefined.