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

Glossary
Unindexed addressing
Means addressing in which the base register value is used directly as the virtual address to send to memory,
without adding or subtracting an offset. In most types of load/store instruction, unindexed addressing is
performed by using offset addressing with an immediate offset of 0. The LDC, LDC2, STC, and STC2 instructions
have an explicit unindexed addressing mode that permits the offset field in the instruction to be used to
specify additional coprocessor options.
UNKNOWN
An UNKNOWN value does not contain valid data, and can vary from moment to moment, instruction to
instruction, and implementation to implementation. An UNKNOWN value must not be a security hole.
UNKNOWN values must not be documented or promoted as having a defined value or effect.
UNK/SBOP
UNKNOWN on reads, Should-Be-One-or-Preserved on writes.
In any implementation, the bit must read as 1, or all 1s for a bit field, and writes to the field must be ignored.
Software must not rely on the bit reading as 1, or all 1s for a bit field, and must use an SBOP policy to write
to the field.
UNK/SBZP
UNKNOWN on reads, Should-Be-Zero-or-Preserved on writes.
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 must not rely on the bit reading as 0, or all 0s for a bit field, and must use an SBZP policy to write
to the field.
UNK Is an abbreviation indicating that software must treat a field as containing an UNKNOWN value.
In any implementation, the bit must read as 0, or all 0s for a bit field. Software must not rely on the field
reading as zero.
UNPREDICTABLE
Means the behavior cannot be relied upon. UNPREDICTABLE behavior must not represent security holes.
UNPREDICTABLE behavior must not halt or hang the processor, or any parts of the system. UNPREDICTABLE
behavior must not be documented or promoted as having a defined effect.
Unsigned data types
Represent a non-negative integer in the range 0 to +2 N −1, using normal binary format.
VA See Virtual address.
VFP Is a coprocessor extension to the ARM architecture. It provides single-precision and double-precision
floating-point arithmetic.
Virtual address (VA)
Is an address generated by an ARM processor. For a PMSA implementation, the virtual address is identical
to the physical address.
Watchpoint
Is a debug event triggered by an access to memory, specified in terms of the address of the location in
memory being accessed.
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