ARM r1p3, R4, R4F - page 452

Glossary
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Load Store Unit (LSU)
The part of a processor that handles load and store transfers.
LSU See Load Store Unit.
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.
Memory coherency A memory is coherent if the value read by a data read or instruction fetch is the value that was
most recently written to that location. Memory coherency is made difficult when there are
multiple possible physical locations that are involved, such as a system that has main memory,
a write buffer and a cache.
Memory Protection Unit (MPU)
Hardware that controls access permissions to blocks of memory. Unlike an MMU, an MPU does
not translate virtual addresses to physical addresses.
Microprocessor See Processor.
Miss See Cache miss.
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.
MPU See Memory Protection Unit.
NaN Not a number. A symbolic entity encoded in a floating-point format that has the maximum
exponent field and a nonzero fraction. An SNaN causes an invalid operand exception if used as
an operand and a most significant fraction bit of zero. A QNaN propagates through almost every
arithmetic operation without signaling exceptions and has a most significant fraction bit of one.
Penalty The number of cycles in which no useful Execute stage pipeline activity can occur because the
instruction flow is different from that assumed or predicted.
Power-on reset See Cold reset.
Prefetching In pipelined processors, the process of fetching instructions from memory to fill up the pipeline
before the preceding instructions have finished executing. Prefetching an instruction does not
mean that the instruction has to be executed.
Prefetch Abort An indication from a memory system to the processor that an instruction has been fetched from
an illegal memory location. An exception must be taken if the processor attempts to execute the
instruction. 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 contraction of microprocessor. A processor includes the CPU or core, plus additional
components such as memory, and interfaces. These are combined as a single macrocell, that can
be fabricated on an integrated circuit.
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 .
Region A partition of instruction or data memory space.