NEC Network Controller uPD98502 - Manual (Page 102)

CHAPTER 2 V R 4120A
102 Preliminary User’s Manual S15543EJ1V0UM
2.4.2 Virtual address space
This section describes the virtual/physical address space and the manner in which virtual addresses are converted
or “translated” into physical addresses in the TLB. The V
R
4120A virtual address can be either 32 or 64 bits wide,
depending on whether the processor is operating in 32-bit or 64-bit mode.
In 32-bit mode, addresses are 32 bits wide. The maximum user process size is 2 Gbytes (2
31
).
In 64-bit mode, addresses are 64 bits wide. The maximum user process size is 1 Tbyte (2
40
).
As shown in Figure 2-25, the virtual address is extended with an address space identifier (ASID), which reduces
the frequency of TLB flushing when switching contexts. This 8-bit ASID is in the CP0 EntryHi register, described later
in this chapter. The Global (G) bit is in the EntryLo0 and EntryLo1 registers, described later in this section.
Figure 2-25. Virtual-to-Physical Address Translation
Virtual address
The offset is then added to the PFN
passing through the TLB.
If there is a match, the page frame
number (PFN) representing the high-
order bits of the physical address is
output from the TLB.
The virtual page number (VPN) in the
virtual address (VA) is compared with
the VPN in the TLB.
TLB
entry
Physical address
3
2
TLB
1
ASID Offset VPN
Offset
PFN
PFN
G ASID VPN