Renesas SH7781 - Manual (Page 218)

7. Memory Management Unit (MMU)
Rev.1.00 Jan. 10, 2008 Page 188 of 1658
REJ09B0261-0100
7.6.7 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.
(1) 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.
(2)
Software Processing (Initial Page Write Exception Handling Routine)
Software is responsible for the following processing:
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. In TLB compatible mode, write to PTEL the values of the PPN, PR, SZ, C, D, SH, V, and WT
bits in the page table entry stored in the address translation table for external memory.
In TLB extended mode, write to PTEL and PTEA the values of the PPN, EPR, ESZ, C, D, SH,
V, and WT bits in the page table entry stored in the address translation table for external
memory.
4. When the entry to be replaced in entry replacement is specified by software, write that value to
the URC bits in MMUCR. If URC is greater than URB at this time, the value should be
changed to an appropriate value after issuing an LDTLB instruction.