ARM Architecture Reference Manual ARMv7-A and ARMv7-R edition

Software can rely on the bit reading as 1, or all 1s for a bit field, and on writes being ignored.
RAZ/SBZP
Read-As-Zero, Should-Be-Zero-or-Preserved on writes.
Glossary
In any implementation, the bit must read as 0, or all 0s for a bit field, and writes to the field must be ignored.
Software can rely on the bit reading as 0, or all 0s for a bit field, but must use an SBZP policy to write to the
field.
RAZ/WI Read-As-Zero, Writes Ignored.
In any implementation, the bit must read as 0, or all 0s for a bit field, and writes to the field must be ignored.
Software can rely on the bit reading as 0, or all 0s for a bit field, and on writes being ignored.
Read-allocate cache
Is a cache in which a cache miss on reading data causes a cache line to be allocated into the cache.
Read-As-One (RAO)
In any implementation, the bit must read as 1, or all 1s for a bit field.
Read-As-Zero (RAZ)
In any implementation, the bit must read as 0, or all 0s for a bit field.
Read, modify, write
In a read, modify, write instruction sequence, a value is read to a general-purpose register, the relevant fields
updated in that register, and the new value written back.
Reserved
Unless otherwise stated:
instructions that are reserved or that access reserved registers have UNPREDICTABLE behavior
bit positions described as Reserved are UNK/SBZP.
RISC Reduced Instruction Set Computer.
Rounding error
Is defined to be the value of the rounded result of an arithmetic operation minus the exact result of the
operation.
Rounding modes
Specify how the exact result of a floating-point operation is rounded to a value that is representable in the
destination format.
Round to Nearest (RN) mode
Means that the rounded result is the nearest representable number to the unrounded result.
Round towards Plus Infinity (RP) mode
Means that the rounded result is the nearest representable number that is greater than or equal to the exact
result.
Round towards Minus Infinity (RM) mode
Means that the rounded result is the nearest representable number that is less than or equal to the exact result.
ARM DDI 0406B Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. Glossary-9