HD6417751 Datasheet, PDF (114/1105 Pages) Renesas Technology Corp – SuperH RISC engine

3.5.5 Avoiding Synonym Problems
When 1- or 4-kbyte pages are recorded in 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 recorded in a number of cache entries, and it becomes impossible to
guarantee data integrity. This problem does not occur with the instruction TLB or instruction
cache. In the SH7751 Series, entry specification is performed using bits [13:5] of the virtual
address in order to achieve fast operand cache operation. However, bits [13:10] of the virtual
address in the case of a 1-kbyte page, and bits [13:12] of the virtual address in the case of a 4-
kbyte page, are subject to address translation. As a result, bits [13:10] of the physical address after
translation may differ from bits [13:10] of the virtual address.
Consequently, the following restrictions apply to the recording of address translation information
in UTLB entries.
1. When address translation information whereby a number of 1-kbyte page UTLB entries are
translated into the same physical address is recorded in the UTLB, ensure that the VPN [13:10]
values are the same.
2. When address translation information whereby a number of 4-kbyte page UTLB entries are
translated into the same physical address is recorded in the UTLB, ensure that the VPN [13:12]
values are the same.
3. Do not use 1-kbyte page UTLB entry physical addresses with UTLB entries of a different page
size.
4. 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. When cache index
mode is used, VPN [25] is used for the entry address instead of VPN [13], and therefore the above
restrictions apply to VPN [25].
Note:
When multiple items of address translation information use the same physical memory to
provide for future SH Series expansion, ensure that the VPN [20:10] values are the same.
Also, do not use the same physical address for address translation information of different
page sizes.
Rev. 3.0, 04/02, page 74 of 1064