Renesas SH7781 - Manual (Page 180)

7. Memory Management Unit (MMU)
Rev.1.00 Jan. 10, 2008 Page 150 of 1658
REJ09B0261-0100
(2) Physical Address Space
This LSI supports a 29-bit physical address space. The physical address space is divided into eight
areas as shown in figure 7.5. Area 7 is a reserved area. For details, see section 11, Local Bus State
Controller (LBSC) section of the hardware manual of the product.
Only when area 7 in the physical address space is accessed using the TLB, addresses H'1C00 0000
to H'1FFF FFFF of area 7 are not designated as a reserved area, but are equivalent to the control
register area in the P4 area, in the virtual address space.
H'0000 0000
H'0400 0000
H'0800 0000
H'0C00 0000
H'1000 0000
H'1400 0000
H'1800 0000
H'1C00 0000
H'1FFF FFFF
Area 0
Area 1
Area 2
Area 3
Area 4
Area 5
Area 6
Area 7 (reserved area)
Figure 7.5 Physical Address Space
(3)
Address Translation
When the MMU is used, the virtual address space is divided into units called pages, and
translation to physical addresses is carried out in these page units. The address translation table in
external memory contains the physical addresses corresponding to virtual addresses and additional
information such as memory protection codes. Fast address translation is achieved by caching the
contents of the address translation table located in external memory into the TLB. In this LSI,
basically, the ITLB is used for instruction accesses and the UTLB for data accesses. In the event
of an access to an area other than the P4 area, the accessed virtual address is translated to a
physical address. If the virtual address belongs to the P1 or P2 area, the physical address is
uniquely determined without accessing the TLB. If the virtual address belongs to the P0, U0, or P3
area, the TLB is searched using the virtual address, and if the virtual address is recorded in the
TLB, a TLB hit is made and the corresponding physical address is read from the TLB. If the
accessed virtual address is not recorded in the TLB, a TLB miss exception is generated and
processing switches to the TLB miss exception handling routine. In the TLB miss exception
handling routine, the address translation table in external memory is searched, and the
corresponding physical address and page management information are recorded in the TLB. After