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

Glossary
Round towards Zero (RZ) mode
Means that results are rounded to the nearest representable number that is no greater in magnitude than the
unrounded result.
Saturated arithmetic
Is integer arithmetic in which a result that would be greater than the largest representable number is set to
the largest representable number, and a result that would be less than the smallest representable number is
set to the smallest representable number. Signed saturated arithmetic is often used in DSP algorithms. It
contrasts with the normal signed integer arithmetic used in ARM processors, in which overflowing results
wrap around from +2 31–1 to –2 31 or vice versa.
SBO See Should-Be-One.
SBOP See Should-Be-One-or-Preserved.
SBZ See Should-Be-Zero.
SBZP See Should-Be-Zero-or-Preserved.
Security hole
Is a mechanism that bypasses system protection.
Self-modifying code
Is code that writes one or more instructions to memory and then executes them. When using self-modifying
code you must use cache maintenance and barrier instructions to ensure synchronization. For details see
Ordering of cache and branch predictor maintenance operations on page B2-21.
Set-associativity
Is the number of cache lines in each of the cache sets in a cache. It can be any number ≥ 1, and is not
restricted to being a power of two.
Should-Be-One (SBO)
Should be written as 1, or all 1s for a bit field, by software. Values other than 1 produce UNPREDICTABLE
results.
Should-Be-One-or-Preserved (SBOP)
Must be written as 1, or all 1s for a bit field, by software if the value is being written without having been
previously read, or if the register has not been initialized. Where the register was previously read on the same
processor, since the processor was last reset, the value in the field should be preserved by writing the value
that was previously read.
Hardware must ignore writes to these fields.
If a value is written to the field that is neither 1 (or all 1s for a bit field), nor a value previously read for the
same field on the same processor, the result is UNPREDICTABLE.
Should-Be-Zero (SBZ)
Should be written as 0, or all 0s for a bit field, by software. Values other than 0 produce UNPREDICTABLE
results.
Glossary-10 Copyright © 1996-1998, 2000, 2004-2008 ARM Limited. All rights reserved. ARM DDI 0406B