Table of Contents
Advertisement
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 SH7750 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 SuperH RISC engine family 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. 4.0, 04/00, page 47 of 850
Advertisement
Table of Contents
