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Rev. 5.00, 09/03, page 70 of 760
3.4.3 MMU Instruction (LDTLB)
The load TLB instruction (LDTLB) is used to record TLB entries. When the IX bit in MMUCR is
0, the LDTLB instruction changes the TLB entry in the way specified by the RC bit in MMUCR
to the value specified by PTEH and PTEL, using VPN bits 16–12 specified in PTEH as the index
number. When the IX bit in MMUCR is 1, the EX-OR of VPN bits 16–12 specified in PTEH and
ASID bits 4–0 in PTEH are used as the index number.
Figure 3.9 shows the case where the IX bit in MMUCR is 0.
When an MMU exception occurs, the virtual page number of the virtual address that caused the
exception is set in PTEH by hardware. The way is set in the RC bit of MMUCR for each
exception (see figure 3.3). Consequently, if the LDTLB instruction is issued after setting only
PTEL in the MMU exception handling routine, TLB entry recording is possible. Any TLB entry
can be updated by software rewriting of PTEH and the RC bits in MMUCR.
As the LDTLB instruction changes address translation information, there is a risk of destroying
address translation information if this instruction is issued in the P0, U0, or P3 area. Make sure,
therefore, that this instruction is issued in the P1 or P2 area. Also, an instruction associated with an
access to the P0, U0, or P3 area (such as the RTE instruction) should be issued at least two
instructions after the LDTLB instruction.