Renesas SH7781 用户手册
7. Memory Management Unit (MMU)
Rev.1.00 Jan. 10, 2008 Page 181 of 1658
REJ09B0261-0100
7.5.5
Avoiding Synonym Problems
When information on 1- or 4-Kbyte pages is written as TLB entries, a synonym problem may
arise. The problem is that, when a number of virtual addresses are mapped onto a single physical
address, the same physical address data is written to a number of cache entries, and it becomes
impossible to guarantee data integrity. This problem does not occur with the instruction TLB and
instruction cache because only data is read in these cases. In this LSI, entry specification is
performed using bits 12 to 5 of the virtual address in order to achieve fast operand cache
operation. However, bits 12 to 10 of the virtual address in the case of a 1-Kbyte page, and bit 12 of
the virtual address in the case of a 4-Kbyte page, are subject to address translation. As a result, bits
12 to 10 of the physical address after translation may differ from bits 12 to 10 of the virtual
address.
arise. The problem is that, when a number of virtual addresses are mapped onto a single physical
address, the same physical address data is written to a number of cache entries, and it becomes
impossible to guarantee data integrity. This problem does not occur with the instruction TLB and
instruction cache because only data is read in these cases. In this LSI, entry specification is
performed using bits 12 to 5 of the virtual address in order to achieve fast operand cache
operation. However, bits 12 to 10 of the virtual address in the case of a 1-Kbyte page, and bit 12 of
the virtual address in the case of a 4-Kbyte page, are subject to address translation. As a result, bits
12 to 10 of the physical address after translation may differ from bits 12 to 10 of the virtual
address.
Consequently, the following restrictions apply to the writing of address translation information as
UTLB entries.
UTLB entries.
• When address translation information whereby a number of 1-Kbyte page UTLB entries are
translated into the same physical address is written to the UTLB, ensure that the VPN[12:10]
values are the same.
values are the same.
• When address translation information whereby a number of 4-Kbyte page UTLB entries are
translated into the same physical address is written to the UTLB, ensure that the VPN[12]
value is the same.
value is the same.
• Do not use 1-Kbyte page UTLB entry physical addresses with UTLB entries of a different
page size.
• Do not use 4-Kbyte page UTLB entry physical addresses with UTLB entries of a different
page size.
The above restrictions apply only when performing accesses using the cache.