TMPR3911 datasheet(92/462 Pages) TOSHIBA

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Chapter 3 CPU Module

3-8

3.3.6.2

Memory System Architecture

The TX39/H’s virtual memory system logically expands the CPU’s physical memory space by

translating addresses composed in a large virtual address space into the physical memory space of

the TX39/H.

Figure 3.3.2 shows the form of an TX39/H virtual address. The most significant 20 bits of a 32-

bit virtual address are called the virtual page number, or VPN. The VPN allows mapping of 4

Kbyte pages, while the least significant 12 bits (the offset within a page) are passed along

unchanged to form the physical address. The three most significant bits of VPN (bits 31..29)

further define how addressed are mapped according to whether the TX39/H is in user mode or

kernel mode (these modes are described in the paragraphs that follow).

0 x x

Kuseg

1 0 0

Kseg0

1 0 1

Kseg1

1 1 x

Kseg2

Offset

VPN

Figure 3.3.2 Virtual Address Format

A 6-bit process identifier field is appended to each virtual address to form unique virtual

addresses for up to 64 processes. The mapping of these extended, process-unique virtual addresses

to physical addresses need not be one-to-one; virtual addresses of two or more different processes

may map to the same physical address.

TMPR3911 Datasheet(PDF) 92 Page - Toshiba Semiconductor