SM320DM6446 datasheet(10/228 Pages) TI1

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2.3.5

Tightly Coupled Memory (TCM)

2.3.6

Advanced High-Performance Bus (AHB)

2.3.7

Embedded Trace Macrocell (ETM) and Embedded Trace Buffer (ETB)

2.3.8

ARM Memory Mapping

2.3.8.1 ARM Internal Memories

SM320DM6446

Digital Media System-on-Chip

SPRS607A – JUNE 2009 – REVISED JUNE 2009

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• Cache maintenance operations provide efficient invalidation of, the entire Dcache or Icache, regions of

the Dcache or Icache, and regions of virtual memory.

The write buffer is used for all writes to a noncachable bufferable region, write-through region and write

misses to a write-back region. A separate buffer is incorporated in the Dcache for holding write-back for

cache line evictions or cleaning of dirty cache lines. The main write buffer has 16-word data buffer and a

four-address buffer. The Dcache write-back has eight data word entries and a single address entry.

ARM internal RAM is provided for storing real-time and performance-critical code/data and the Interrupt

Vector table. ARM internal ROM enables non-EMIFA boot options, such as NAND and UART. The RAM

and ROM memories interfaced to the ARM926EJ-S via the tightly coupled memory interface that provides

for separate instruction and data bus connections. Since the ARM TCM does not allow instructions on the

D-TCM bus or data on the I-TCM bus, an arbiter is included so that both data and instructions can be

stored in the internal RAM/ROM. The arbiter also allows accesses to the RAM/ROM from extra-ARM

sources (e.g., EDMA or other masters). The ARM926EJ-S has built-in DMA support for direct accesses to

the ARM internal memory from a non-ARM master. Because of the time-critical nature of the TCM link to

the ARM internal memory, all accesses from non-ARM devices are treated as DMA transfers.

Instruction and Data accesses are differentiated via accessing different memory map regions, with the

instruction region from 0x0000 through 0x7FFF and data from 0x8000 through 0xFFFF. The instruction

region at 0x0000 and data region at 0x8000 map to the same physical 16KB TCM RAM. Placing the

instruction region at 0x0000 is necessary to allow the ARM Interrupt Vector table to be placed at 0x0000,

as required by the ARM architecture. The internal 16-KB RAM is split into two physical banks of 8KB

each, which allows simultaneous instruction and data accesses to be accomplished if the code and data

are in separate banks.

The ARM Subsystem uses the AHB port of the ARM926EJ-S to connect the ARM to the Config bus and

the external memories. Arbiters are employed to arbitrate access to the separate D-AHB and I-AHB by the

Config Bus and the external memories bus.

To support real-time trace, the ARM926EJ-S processor provides an interface to enable connection of an

Embedded Trace Macrocell (ETM). The ARM926ES-J Subsystem in the DM6446 also includes the

Embedded Trace Buffer (ETB). The ETM consists of two parts:

• Trace Port provides real-time trace capability for the ARM9.

• Triggering facilities provide trigger resources, which include address and data comparators, counter,

and sequencers.

The DM6446 trace port is not pinned out and is instead only connected to the Embedded Trace Buffer.

The ETB has a 4KB buffer memory. ETB enabled debug tools are required to read/interpret the captured

trace data.

The ARM memory map is shown in Section 2.5, Memory Map Summary of this document. The ARM has

access to memories shown in the following sections.

The ARM has access to the following ARM internal memories:

• 16KB ARM Internal RAM on TCM interface, logically separated into two 8KB pages to allow

simultaneous access on any given cycle if there are separate accesses for code (I-TCM bus) and data

(D-TCM) to the different memory regions.

• 8KB ARM Internal ROM

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