HD6417706 Datasheet, PDF (108/709 Pages) Renesas Technology Corp – Renesas 32-Bit RISC Microcomputer Super RISC engine Family/SH7700 Series

3.3.3 TLB Address Comparison
The results of address comparison determine whether a specific virtual page number is registered
in the TLB. The virtual page number of the virtual address that accesses external memory is
compared to the virtual page number of the indexed TLB entry. The ASID within the PTEH is
compared to the ASID of the indexed TLB entry. All four ways are searched simultaneously. If the
compared values match, and the indexed TLB entry is valid (V bit = 1), the hit is registered.
It is necessary to have software ensure that TLB hits do not occur simultaneously in more than one
way, as hardware operation is not guaranteed if this occurs. For example, if there are two identical
TLB entries with the same VPN and a setting is made such that a TLB hit is made only by a
process with ASID = H'FF when one is in the shared state (SH = 1) and the other in the non-shared
state (SH = 0), then if the ASID in PTEH is set to H'FF, there is a possibility of simultaneous TLB
hits in both these ways. It is therefore necessary to ensure that this kind of setting is not made by
software.
The object compared varies depending on the page management information (SZ, SH) in the TLB
entry. It also varies depending on whether the system supports multiple virtual memory or single
virtual memory.
The page-size information determines whether VPN (11, 10) is compared. VPN (11, 10) is
compared for 1-kbyte pages (SZ = 0) but not for 4-kbyte pages (SZ = 1).
The sharing information (SH) determines whether the PTEH.ASID and the ASID in the TLB entry
are compared. ASIDs are compared when there is no sharing between processes (SH = 0) but not
when there is sharing (SH = 1).
When single virtual memory is supported (MMUCR.SV = 1) and privileged mode is engaged
(SR.MD = 1), all process resources can be accessed. This means that ASIDs are not compared
when single virtual memory is supported and privileged mode is engaged. The objects of address
comparison are shown in figure 3.7.
Rev. 4.00, 03/04, page 62 of 660