AVR32AP datasheet(50/181 Pages) ATMEL

50 / 181 page

32001A–AVR32–06/06

AVR32

Figure 4-2.

The AVR32 segment translation map

4.2

Understanding the MMU

The AVR32 Memory Management Unit (MMU) is responsible for mapping virtual to physical

addresses. When a memory access is performed, the MMU translates the virtual address speci-

fied into a physical address, while checking the access permissions. If an error occurs in the

translation process, or operating system intervention is needed for some reason, the MMU will

issue an exception, allowing the problem to be resolved by software.

The MMU architecture uses paging to map memory pages from the 32-bit virtual address space

to a 32-bit physical address space. Page sizes of 1, 4, 64 Kbytes and 1 Mbyte are supported.

Each page has individual access rights, providing fine protection granularity.

The information needed in order to perform the virtual-to-physical mapping resides in a page

table. Each page has its own entry in the page table. The page table also contains protection

information and other data needed in the translation process. Conceptually, the page table is

accessed for every memory access, in order to read the mapping information for each page.

4.2.1

Virtual Memory Models

The MMU provides two different virtual memory models, selected by the Mode (M) bit in the

MMU Control Register:

• Shared virtual memory, where the same virtual address space is shared between all

processes

• Private virtual memory, where each process has its own virtual address space

In shared virtual memory, the virtual address uniquely identifies which physical address it should

be mapped to. Two different processes addressing the same virtual address will always access

2GB translated space

cacheable

512MB system space,

non-cacheable

512MB translated space,

cacheable

512MB non-translated

space, non-cacheable

512MB non-translated

space, cacheable

0x00000000

0x80000000

0xA0000000

0xC0000000

0xE0000000

0xFFFFFFFF

P0 / U0

2GB physical address

space

Virtual address space

512MB physical address

space

0x00000000

0x80000000

0xE0000000

0xFFFFFFFF

0x20000000

Physical address space

Segment

translation

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