Glossary

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

Abort

A mechanism that indicates to a core that it must halt execution of an attempted illegal memory access. An abort can be caused by the external or internal memory system as a result of attempting to access invalid instruction or data memory. An abort is classified as either a Prefetch or Data Abort, and an internal or External Abort.

See Also Data Abort, External Abort and Prefetch Abort.

Advanced eXtensible Interface (AXI)

This is a bus protocol that supports separate address/control and data phases, unaligned data transfers using byte strobes, burst-based transactions with only start address issued, separate read and write data channels to enable low-cost DMA, ability to issue multiple outstanding addresses, out-of-order transaction completion, and easy addition of register stages to provide timing closure.The AXI protocol also includes optional extensions to cover signaling for low-power operation.

AXI is targeted at high performance, high clock frequency system designs and includes a number of features that make it very suitable for high speed sub-micron interconnect.

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)

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.

AHB Access Port (AHB-AP)

An optional component of the DAP that provides an AHB interface to an SoC.

AHB-AP

See AHB Access Port.

AHB-Lite

AHB-Lite is a subset of the full AHB specification. It is intended for use in designs where only a single AHB master is used. This can be a simple single AHB master system or a multi-layer AHB system where there is only one AHB master on a layer.

AMBA

See Advanced Microcontroller Bus Architecture.

AMBA Trace Bus (ATB)

A bus used by trace devices to share CoreSight capture resources.

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.

Architecture

The organization of hardware and/or software that characterizes a processor and its attached components, and enables devices with similar characteristics to be grouped together when describing their behavior, for example, Harvard architecture, instruction set architecture, ARMv6 architecture.

ASIC

See Application Specific Integrated Circuit.

ATB

See AMBA Trace Bus.

ATB bridge

A synchronous ATB bridge provides a register slice to facilitate timing closure through the addition of a pipeline stage. It also provides a unidirectional link between two synchronous ATB domains.

An asynchronous ATB bridge provides a unidirectional link between two ATB domains with asynchronous clocks. It is intended to support connection of components with ATB ports residing in different clock domains.

ATPG

See Automatic Test Pattern Generation.

Automatic Test Pattern Generation (ATPG)

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

AXI

See Advanced eXstensible Interface.

Banked registers

Those physical registers whose use is defined by the current processor mode. The banked registers are r8 to r14.

Beat

Alternative word for an individual transfer within a burst. For example, an INCR4 burst comprises four beats.

See Also Burst.

Boundary scan chain

A boundary scan chain is made up of serially-connected devices that implement boundary scan technology using a standard JTAG TAP interface. Each device contains at least one TAP controller containing shift registers that form the chain connected between TDI and TDO, through which test data is shifted. Processors can contain several shift registers to enable you to access selected parts of the device.

Breakpoint

A breakpoint is a mechanism provided by debuggers to identify an instruction at which program execution is to be halted. Breakpoints are inserted by the programmer to enable inspection of register contents, memory locations, variable values at fixed points in the program execution to test that the program is operating correctly. Breakpoints are removed after the program is successfully tested.

See Also Watchpoint.

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, four-beat, eight-beat, or 16-beat bursts, and to specify how the addresses are incremented.

See Also Beat.

Byte

An 8-bit data item.

Byte lane strobe

An AHB signal, HBSTRB, that is used for unaligned or mixed-endian data accesses to determine which byte lanes are active in a transfer. One bit of HBSTRB corresponds to eight bits of the data bus.

Clock gating

Gating a clock signal for a macrocell with a control signal and using the modified clock that results to control the operating state of the macrocell.

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.

Coprocessor

A processor that supplements the main processor. It carries out additional functions that the main processor cannot perform. Usually used for floating-point math calculations, signal processing, or memory management.

Core

A core is that part of a processor that contains the ALU, the datapath, the general-purpose registers, the Program Counter, and the instruction decode and control circuitry.

Core reset

See Warm reset.

Cross Trigger Interface (CTI)

Part of an Embedded Cross Trigger device. The CTI provides the interface between a core/ETM and the CTM within an ECT.

Cross Trigger Matrix (CTM)

The CTM combines the trigger requests generated from CTIs and broadcasts them to all CTIs as channel triggers within an Embedded Cross Trigger device.

CTI

See Cross Trigger Interface.

CTM

See Cross Trigger Matrix.

CoreSight

The infrastructure for monitoring, tracing, and debugging a complete system on chip.

DBGTAP

See Debug Test Access Port.

Debug Access Port (DAP)

A TAP block that acts as an AMBA (AHB or AHB-Lite) master for access to a system bus. The DAP is the term used to encompass a set of modular blocks that support system wide debug. The DAP is a modular component, intended to be extendable to support optional access to multiple systems such as memory mapped AHB and CoreSight APB through a single debug interface.

Debugger

A debugging system that includes a program, used to detect, locate, and correct software faults, together with custom hardware that supports software debugging.

Debug Test Access Port (DBGTAP)

The collection of four mandatory and one optional terminals that form the input/output and control interface to a JTAG boundary-scan architecture. The mandatory terminals are DBGTDI, DBGTDO, DBGTMS, and TCK. The optional terminal is TRST. This signal is mandatory in ARM cores because it is used to reset the debug logic.

ECT

See Embedded Cross Trigger.

Embedded Cross Trigger (ECT)

The ECT is a modular component to support the interaction and synchronization of multiple triggering events with an SoC.

EmbeddedICE logic

An on-chip logic block that provides TAP-based debug support for ARM processor cores. It is accessed through the TAP controller on the ARM core using the JTAG interface.

EmbeddedICE-RT

The JTAG-based hardware provided by debuggable ARM processors to aid debugging in real-time.

Embedded Trace Buffer

The ETB provides on-chip storage of trace data using a configurable sized RAM.

Embedded Trace Macrocell (ETM)

A hardware macrocell that, when connected to a processor core, outputs instruction and data trace information on a trace port. The ETM provides processor driven trace through a trace port compliant to the ATB protocol.

ETB

See Embedded Trace Buffer.

ETM

See Embedded Trace Macrocell.

Event

1 (Simple) An observable condition that can be used by an ETM to control aspects of a trace.

2 (Complex) A boolean combination of simple events that is used by an ETM to control aspects of a trace.

External Abort

An indication from an external memory system to a core that it must halt execution of an attempted illegal memory access. An External Abort is caused by the external memory system as a result of attempting to access invalid memory.

See Also Abort, Data Abort and Prefetch Abort.

Formatter

The formatter is an internal input block in the ETB and TPIU that embeds the trace source ID within the data to create a single trace stream.

Half-rate clocking (ETM)

Dividing the trace clock by two so that the TPA can sample trace data signals on both the rising and falling edges of the trace clock. The primary purpose of half-rate clocking is to reduce the signal transition rate on the trace clock of an ASIC for very high-speed systems.

Halfword

A 16-bit data item.

Host

A computer that provides data and other services to another computer. Especially, a computer providing debugging services to a target being debugged.

IEM

See Intelligent Energy Management.

Illegal instruction

An instruction that is architecturally Undefined.

Implementation-defined

Means that the behavior is not architecturally defined, but should be defined and documented by individual implementations.

Implementation-specific

Means that the behavior is not architecturally defined, and does not have to be documented by individual implementations. Used when there are a number of implementation options available and the option chosen does not affect software compatibility.

Imprecise tracing

A filtering configuration where instruction or data tracing can start or finish earlier or later than expected. Most cases cause tracing to start or finish later than expected.

For example, if TraceEnable is configured to use a counter so that tracing begins after the fourth write to a location in memory, the instruction that caused the fourth write is not traced, although subsequent instructions are. This is because the use of a counter in the TraceEnable configuration always results in imprecise tracing.

Intelligent Energy Management (IEM)

A technology that enables dynamic voltage scaling and clock frequency variation to be used to reduce power consumption in a device.

Internal scan chain

A series of registers connected together to form a path through a device, used during production testing to import test patterns into internal nodes of the device and export the resulting values.

Joint Test Action Group (JTAG)

The name of the organization that developed standard IEEE 1149.1. This standard defines a boundary-scan architecture used for in-circuit testing of integrated circuit devices. It is commonly known by the initials JTAG.

JTAG

See Joint Test Action Group.

JTAG Access Port (JTAG-AP)

An optional component of the DAP that provides JTAG access to on-chip components, operating as a JTAG master port to drive JTAG chains throughout a SoC.

JTAG-AP

See JTAG Access Port.

JTAG Debug Port (JTAG-DP)

An optional external interface for the DAP that provides a standard JTAG interface for debug access.

JTAG-DP

See JTAG Debug Port.

Macrocell

A complex logic block with a defined interface and behavior. A typical VLSI system comprises several macrocells (such as a processor, an ETM, and a memory block) plus application-specific logic.

Microprocessor

See Processor.

Monitor debug-mode

One of two mutually exclusive debug modes. In Monitor debug-mode the processor enables a software abort handler provided by the debug monitor or operating system debug task. When a breakpoint or watchpoint is encountered, this enables vital system interrupts to continue to be serviced while normal program execution is suspended.

See Also Halt mode.

Multi-ICE

A JTAG-based tool for debugging embedded systems.

Multi-layered

An AMBA scheme to break a bus into segments that are controlled in access. This enables local masters to reduce lock overhead.

Multi master

An AMBA bus sharing scheme (not in AMBA Lite) where different masters can gain a bus lock (Grant) to access the bus in an interleaved fashion.

Power-on reset

See Cold reset.

Prefetch Abort

An indication from a memory system to a core that it must halt execution of an attempted illegal memory access. A Prefetch Abort can be caused by the external or internal memory system as a result of attempting to access invalid instruction memory.

See Also Data Abort, External Abort and Abort.

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.

Read

Reads are defined as memory operations that have the semantics of a load. That is, the ARM instructions LDM, LDRD, LDC, LDR, LDRT, LDRSH, LDRH, LDRSB, LDRB, LDRBT, LDREX, RFE, STREX, SWP, and SWPB, and the Thumb instructions LDM, LDR, LDRSH, LDRH, LDRSB, LDRB, and POP. Java instructions that are accelerated by hardware can cause a number of reads to occur, according to the state of the Java stack and the implementation of the Java hardware acceleration.

RealView ICE

A system for debugging embedded processor cores using a JTAG interface.

Replicator

A replicator enables two trace sinks to be wired together and to operate independently on the same incoming trace stream. The input trace stream is output onto two (independent) ATB ports.

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.

SBO

See Should Be One.

SBZ

See Should Be Zero.

SBZP

See Should Be Zero or Preserved.

Scan chain

A scan chain is made up of serially-connected devices that implement boundary scan technology using a standard JTAG TAP interface. Each device contains at least one TAP controller containing shift registers that form the chain connected between TDI and TDO, through which test data is shifted. Processors can contain several shift registers to enable you to access selected parts of the device.

SCREG

The currently selected scan chain number in an ARM TAP controller.

Serial Wire Debug Port

An optional external interface for the DAP that provides a serial-wire bidirectional debug interface.

Should Be One (SBO)

Should be written as 1 (or all 1s for bit fields) by software. Writing a 0 produces Unpredictable results.

Should Be Zero (SBZ)

Should be written as 0 (or all 0s for bit fields) by software. Writing a 1 produces Unpredictable results.

Should Be Zero or Preserved (SBZP)

Should be written as 0 (or all 0s for bit fields) by software, or preserved by writing the same value back that has been previously read from the same field on the same processor.

SW-DP

See Serial Wire Debug Port.

TAP

See Test access port.

TCD

See Trace Capture Device.

Test Access Port (TAP)

The collection of four mandatory and one optional terminals that form the input/output and control interface to a JTAG boundary-scan architecture. The mandatory terminals are TDI, TDO, TMS, and TCK. The optional terminal is TRST. This signal is mandatory in ARM cores because it is used to reset the debug logic.

TPA

See Trace Port Analyzer.

TPIU

See Trace Port Interface Unit.

Trace Capture Device (TCD)

A generic term to describe Trace Port Analyzers, logic analyzers, and on-chip trace buffers.

Trace driver

A Remote Debug Interface target that controls a piece of trace hardware. That is, the trigger macrocell, trace macrocell, and trace capture tool.

Trace funnel

A device that combines multiple trace sources onto a single bus.

Trace hardware

A term for a device that contains an Embedded Trace Macrocell.

Trace port

A port on a device, such as a processor or ASIC, used to output trace information.

Trace Port Analyzer (TPA)

A hardware device that captures trace information output on a trace port. This can be a low-cost product designed specifically for trace acquisition, or a logic analyzer.

Trace Port Interface Unit (TPIU)

The TPIU is used to drain trace data and acts as a bridge between the on-chip trace data and the data stream captured by a TPA.

Undefined

Indicates an instruction that generates an Undefined instruction trap. See the ARM Architecture Reference Manual for more details on ARM exceptions.

UNP

See Unpredictable.

Unpredictable

Means that the behavior of the ETM cannot be relied upon. Such conditions have not been validated. When applied to the programming of an event resource, only the output of that event resource is Unpredictable.Unpredictable behavior can affect the behavior of the entire system, because the ETM is capable of causing the core to enter debug state, and external outputs may be used for other purposes.

Unpredictable

For reads, the data returned when reading from this location is unpredictable. It can have any value. For writes, writing to this location causes unpredictable behavior, or an unpredictable change in device configuration. Unpredictable instructions must not halt or hang the processor, or any part of the system.

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.

Watchpoint

A watchpoint is a mechanism provided by debuggers to halt program execution when the data contained by a particular memory address is changed. Watchpoints are inserted by the programmer to allow inspection of register contents, memory locations, and variable values when memory is written to test that the program is operating correctly. Watchpoints are removed after the program is successfully tested.

See Also Breakpoint.

Word

A 32-bit data item.

Write

Writes are defined as operations that have the semantics of a store. That is, the ARM instructions SRS, STM, STRD, STC, STRT, STRH, STRB, STRBT, STREX, SWP, and SWPB, and the Thumb instructions STM, STR, STRH, STRB, and PUSH. Java instructions that are accelerated by hardware can cause a number of writes to occur, according to the state of the Java stack and the implementation of the Java hardware acceleration.

Write buffer

A block of high-speed memory, arranged as a FIFO buffer, between the data cache and main memory, whose purpose is to optimize stores to main memory.

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