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Glossary

This glossary describes some of the terms used in this manual. Where terms can have several meanings, the meaning presented here is intended.

Advanced High-performance Bus (AHB)

The AMBA Advanced High-performance Bus system connects embedded processors such as an ARM core to high-performance peripherals, DMA controllers, on-chip memory, and interfaces. It is a high-speed, high-bandwidth bus that supports multi-master bus management to maximize system performance.

See Also Advanced Microcontroller Bus Architecture and AHB-Lite.

Advanced Microcontroller Bus Architecture (AMBA)

The ARM open standard for on-chip buses. AHB conforms to this standard.

AMBA is the ARM open standard for multi-master on-chip buses, capable of running with multiple masters and slaves. It is an on-chip bus specification that details a strategy for the interconnection and management of functional blocks that make up a System-on-Chip (SoC). It aids in the development of embedded processors with one or more CPUs or signal processors and multiple peripherals. AMBA complements a reusable design methodology by defining a common backbone for SoC modules. AHB conforms to this standard.

Advanced Peripheral Bus (APB)

The AMBA Advanced Peripheral Bus is a simpler bus protocol than AHB. It is designed for use with ancillary or general-purpose peripherals such as timers, interrupt controllers, UARTs, and I/O ports. Connection to the main system bus is through a system-to-peripheral bus bridge that helps to reduce system power consumption.

See Also Advanced High-performance Bus.

AHB

See Advanced High-performance Bus.

Aligned

Aligned data items are stored so that their address is divisible by the highest power of two that divides their size. Aligned words and halfwords have addresses that are divisible by four and two respectively. The terms word-aligned and halfword-aligned therefore stipulate addresses that are divisible by four and two respectively. Other related terms are defined similarly.

AMBA

See Advanced Microcontroller Bus Architecture.

APB

See Advanced Peripheral Bus.

Application Specific Integrated Circuit (ASIC)

An integrated circuit that has been designed to perform a specific application function. It can be custom-built or mass-produced.

ASIC

See Application Specific Integrated Circuit.

Automatic Test Pattern Generation (ATPG)

The process of automatically generating manufacturing test vectors for an ASIC design, using a specialized software tool.

Big-endian

Byte ordering scheme in which bytes of decreasing significance in a data word are stored at increasing addresses in memory.

See Also Little-endian and Endianness.

Big-endian memory

Memory in which:- a byte or halfword at a word-aligned address is the most significant byte or halfword within the word at that address - a byte at a halfword-aligned address is the most significant byte within the halfword at that address.

See Also Little-endian memory.

Burst

A group of transfers to consecutive addresses. Because the addresses are consecutive, there is no requirement to supply an address for any of the transfers after the first one. This increases the speed at which the group of transfers can occur. Bursts over AHB buses are controlled using the HBURST signals to specify if transfers are single, 4-beat, 8-beat, or 16-beat bursts, and to specify how the addresses are incremented.

See Also Beat.

Byte

An 8-bit data item.

Cold reset

Also known as power-on reset. Starting the processor by turning power on. Turning power off and then back on again clears main memory and many internal settings. Some program failures can lock up the processor and require a cold reset to enable the system to be used again. In other cases, only a warm reset is required.

See Also Warm reset.

DNM

See Do Not Modify.

Do Not Modify (DNM)

In Do Not Modify fields, the value must not be altered by software. DNM fields read as Unpredictable values, and must only be written with the same value read from the same field on the same processor. Throughout this manual, DNM fields are sometimes followed by RAZ or RAO in parentheses to show which way the bits should read for future compatibility, but programmers must not rely on this behavior.

Endianness

Byte ordering. The scheme that determines the order in which successive bytes of a data word are stored in memory. An aspect of the system’s memory mapping.

See Also Little-endian and Big-endian.

Halfword

A 16-bit data item.

Little-endian

Byte ordering scheme in which bytes of increasing significance in a data word are stored at increasing addresses in memory.

See Also Big-endian and Endianness.

Little-endian memory

Memory in which: - a byte or halfword at a word-aligned address is the least significant byte or halfword within the word at that address - a byte at a halfword-aligned address is the least significant byte within the halfword at that address.

See Also Big-endian memory.

Microprocessor

See Processor.

Power-on reset

See Cold reset.

Processor

A processor is the circuitry in a computer system required to process data using the computer instructions. It is an abbreviation of microprocessor. A clock source, power supplies, and main memory are also required to create a minimum complete working computer system.

Remapping

Changing the address of physical memory or devices after the application has started executing. This is typically done to allow RAM to replace ROM when the initialization has been completed.

Reserved

A field in a control register or instruction format is reserved if the field is to be defined by the implementation, or produces Unpredictable results if the contents of the field are not zero. These fields are reserved for use in future extensions of the architecture or are implementation-specific. All reserved bits not used by the implementation must be written as 0 and read as 0.

Warm reset

Also known as a core reset. Initializes the majority of the processor excluding the debug controller and debug logic. This type of reset is useful if you are using the debugging features of a processor.

Word

A 32-bit data item.

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