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CS 220 / ARM / ARM1176JZ-S Technical Reference Mmanual.pdf
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Chapter 7

Level One Memory System

This chapter describes the processor level one memory system. It contains the following sections:

About the level one memory system on page 7-2

Cache organization on page 7-3

Tightly-coupled memory on page 7-7

DMA on page 7-10

TCM and cache interactions on page 7-12

Write buffer on page 7-16.

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Level One Memory System

7.1About the level one memory system

The processor level one memory system consists of:

separate Instruction and Data Caches in a Harvard arrangement

separate Instruction and Data Tightly-Coupled Memory (TCM) areas

a DMA system for accessing the TCMs

a Write Buffer

two MicroTLBs, backed by a main TLB.

Each cache line can contain Secure or Non-secure data. In parallel with each of the caches is an area of dedicated RAM on both the instruction and data sides. These regions are referred to as TCM. You can implement 0, 1 or 2 TCMs on each of the Instruction and Data sides.

You can configure each TCM to contain Secure or Non-secure data. Each TCM has a dedicated base address that you can place anywhere in the physical address map, and does not have to be backed by memory implemented externally. The Instruction and Data TCMs have separate base addresses. A DMA mechanism can access TCMs and this enables loads from or stores to another location in memory while the processor core is running.

The MMU provides the facilities required by sophisticated operating systems to deliver protected virtual memory environments and demand paging. It also supports real-time tasks with features that provide predictable execution time.

A full MMU handles address translation for each of the instruction and data sides. The MMU is responsible for protection checking, address translation, and memory attributes, some of which can be passed to the level two memory system. The cache stores each Non-secure memory region attribute, NS attribute, along with each cache line as an NS Tag.

The processor caches memory translations in MicroTLBs for each of the instruction and data sides and for the DMA, with a single main TLB backing the MicroTLBs.

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