SH7751 Datasheet, PDF (191/1224 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

3. Memory Management Unit (MMU)
3.6.7 Initial Page Write Exception
An initial page write exception occurs when the D bit is 0 even though a UTLB entry contains
address translation information matching the virtual address to which a data access (write) is
made, and the access is permitted. The initial page write exception processing carried out by
hardware and software is shown below.
Hardware Processing: In the event of an initial page write 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'080 in EXPEVT.
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 initial page write exception handling routine.
Software Processing (Initial Page Write Exception Handling Routine): The following
processing should be carried out as the responsibility of software:
1. Retrieve the necessary page table entry from external memory.
2. Write 1 to the D bit in the external memory page table entry.
3. Write to PTEL the values of the PPN, PR, SZ, C, D, WT, SH, and V bits in the page table
entry recorded in external memory. If necessary, the values of the SA and TC bits should be
written to PTEA.
4. 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.
5. Execute the LDTLB instruction and write the contents of PTEH, PTEL, and PTEA to the
UTLB.
Rev.4.00 Oct. 10, 2008 Page 93 of 1122
REJ09B0370-0400