Hitachi SH7751 Hardware Manual page 96

Longword access to MMUCR can be performed from H'FF00 0010 in the P4 area and H'1F00
0010 in area 7. The individual bits perform MMU settings as shown below. Therefore, MMUCR
rewriting should be performed by a program in the P1 or P2 area. After MMUCR is updated, an
instruction that performs data access to the P0, P3, U0, or store queue area should be located at
least four instructions after the MMUCR update instruction. Also, a branch instruction to the P0,
P3, or U0 area should be located at least eight instructions after the MMUCR update instruction.
MMUCR contents can be changed by software. The LRUI bits and URC bits may also be updated
by hardware.


LRUI: LRU bits that indicate the ITLB entry for which replacement is to be performed. The
LRU (least recently used) method is used to decide the ITLB entry to be replaced in the event
of an ITLB miss. The entry to be purged from the ITLB can be confirmed using the LRUI bits.
LRUI is updated by means of the algorithm shown below. A dash in this table means that
updating is not performed.
When ITLB entry 0 is used
When ITLB entry 1 is used
When ITLB entry 2 is used
When ITLB entry 3 is used
Other than the above
When the LRUI bit settings are as shown below, the corresponding ITLB entry is updated by
an ITLB miss. An asterisk in this table means "Don't care".
ITLB entry 0 is updated
ITLB entry 1 is updated
ITLB entry 2 is updated
ITLB entry 3 is updated
Other than the above
Ensure that values for which "Setting prohibited" is indicated in the above table are not set at
the discretion of software. After a power-on or manual reset the LRUI bits are initialized to 0,
and therefore a prohibited setting is never made by a hardware update.


URB: Bits that indicate the UTLB entry boundary at which replacement is to be performed.
Valid only when URB > 0.
[5] [4] [3]
0 0 0
1 — —
— 1 —
— — 1
— — —
[5] [4] [3]
1 1 1
0
* *
0
* *
0
* *
Setting prohibited
LRUI
[2] [1] [0]
— — —
0 0 —
1 — 0
— 1 1
— — —
LRUI
[2] [1] [0]
* * *
1 1
*
0 1
*
0 0
*
Rev. 3.0, 04/02, page 57 of 1064