SH7730 Datasheet, PDF (233/1188 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer SuperHTM RISC engine Family / SH7780 Series

Section 7 Memory Management Unit (MMU)
7.5.5 Avoiding Synonym Problems
The following explanation is for the case with 32-Kbyte operand cache.
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.
Consequently, the following restrictions apply to the writing of address translation information as
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.
• 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.
• 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.
For cache sizes other than 32 Kbytes, the page sizes that can lead to synonym problems and the
bits in VPN the value of which should be matched at the time of writing entries to the UTBL are
different from those shown in the above explanation. The page sizes that can lead to synonym
problems are shown in table 7.3 for cache sizes of 8 Kbytes to 64 Kbytes.
Rev. 1.00 Sep. 19, 2007 Page 185 of 1136
REJ09B0359-0100