NEC Network Controller uPD98502 - Manual (Page 104)

CHAPTER 2 V R 4120A
104 Preliminary User’s Manual S15543EJ1V0UM
2.4.2.2 32-bit mode address translation
Figure 2-26 shows the virtual-to-physical-address translation of a 32-bit mode address. The pages can have five
different sizes between 1 Kbyte (10 bits) and 256 Kbytes (18 bits), each being 4 times as large as the preceding one
in ascending order, that is 1 K, 4 K, 16 K, 64 K, and 256 K.
— Shown at the top of Figure 2-26 is the virtual address space in which the page size is 1 Kbyte and the offset
is 10 bits. The 22 bits excluding the ASID field represents the virtual page number (VPN), enabling selecting
a page table of 4 M entries.
— Shown at the bottom of Figure 2-26 is the virtual address space in which the page size is 256 Kbytes and the
offset is 18 bits. The 14 bits excluding the ASID field represents the VPN, enabling selecting a page table of
16 K entries.
Figure 2-26. 32-bit Mode Virtual Address Translation
Bits 31 to 29 of the virtual
address select the user,
supervisor, or kernel
address space.
31
PFN
Virtual address for 16 K (2
14
) 256-Kbyte pages
Virtual address for 4M (2 22 ) 1-Kbyte pages
22 bits = 4 M pages
The offset is passed to
physical address without
being changed.
The offset is passed to
physical address without
being changed.
Virtual-to-physical address
translation with the TLB
Virtual-to-physical address
translation with the TLB
10 22 8
0
0 9 10 28 29 31 32 39
ASID
Offset
VPN Offset
TLB
14 bits = 16 K pages
18 14 8
0 17 18 28 29 31 32 39
ASID VPN Offset
TLB
32-bit physical address