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Software Processing (Data TLB Miss Exception Handling Routine): Software is responsible
for searching the external memory page table and assigning the necessary page table entry.
Software should carry out the following processing in order to find and assign the necessary page
table entry.
1. Write to PTEL the values of the PPN, PR, SZ, C, D, SH, V, and WT bits in the page table
entry recorded in the external memory address translation table. If necessary, the values of the
SA and TC bits should be written to PTEA.
2. When the entry to be replaced in entry replacement is specified by software, write that value to
URC in the MMUCR register. If URC is greater than URB at this time, the value should be
changed to an appropriate value after issuing an LDTLB instruction.
3. Execute the LDTLB instruction and write the contents of PTEH, PTEL, and PTEA to the
UTLB.
4. Finally, execute the exception handling return instruction (RTE), terminate the exception
handling routine, and return control to the normal flow. The RTE instruction should be issued
at least one instruction after the LDTLB instruction.
3.6.6
Data TLB Protection Violation Exception
A data TLB protection violation exception occurs when, even though a UTLB entry contains
address translation information matching the virtual address to which a data access is made, the
actual access type is not permitted by the access right specified by the PR bit. The data TLB
protection violation exception processing carried out by hardware and software is shown below.
Hardware Processing: In the event of a data TLB protection violation exception, hardware
carries out the following processing:
1. Sets the VPN of the virtual address at which the exception occurred in PTEH.
2. Sets the virtual address at which the exception occurred in TEA.
3. Sets exception code H'0A0 in the case of a read, or H'0C0 in the case of a write, in EXPEVT
(OCBP, OCBWB: read; OCBI, MOVCA.L: write).
4. Sets the PC value indicating the address of the instruction at which the exception occurred in
SPC. If the exception occurred at a delay slot, sets the PC value indicating the address of the
delayed branch instruction in SPC.
5. Sets the SR contents at the time of the exception in SSR. The R15 contents at this time are
saved in SGR.
6. Sets the MD bit in SR to 1, and switches to privileged mode.
7. Sets the BL bit in SR to 1, and masks subsequent exception requests.
8. Sets the RB bit in SR to 1.
9. Branches to the address obtained by adding offset H'0000 0100 to the contents of VBR, and
starts the data TLB protection violation exception handling routine.
Rev. 4.0, 04/00, page 52 of 850
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