CSCI E-92: Application Note 14

ARM Acronym Glossary
--------------------

RAO
  See Read-As-One (RAO).

RAO/SBOP
  Read-As-One, Should-Be-One-or-Preserved on writes.

  Hardware must implement the field as Read-as-One, and must ignore
  writes to the field.

  Software can rely on the field reading as all 1s, but must use an
  SBOP policy to write to the field.

  This description can apply to a single bit that reads as 1, or to a
  field that reads as all 1s.

RAO/WI
  Read-As-One, Writes Ignored.

  Hardware must implement the field as Read-as-One, and must ignore
  writes to the field.

  Software can rely on the field reading as all 1s, and on writes
  being ignored.

  This description can apply to a single bit that reads as 1, or to a
  field that reads as all 1s.

RAZ
  See Read-As-Zero (RAZ).

RAZ/SBZP
  Read-As-Zero, Should-Be-Zero-or-Preserved on writes.

  Hardware must implement the field as Read-as-Zero, and must ignore
  writes to the field.

  Software can rely on the field reading as all 0s, but must use an
  SBZP policy to write to the field.

  This description can apply to a single bit that reads as 0, or to a
  field that reads as all 0s.

RAZ/WI
  Read-As-Zero, Writes Ignored.

  Hardware must implement the field as Read-as-Zero, and must ignore
  writes to the field.

  Software can rely on the field reading as all 0s, and on writes
  being ignored.

  This description can apply to a single bit that reads as 0, or to a
  field that reads as all 0s.

Read-As-One (RAO)
  Hardware must implement the field as reading as all 1s.

  Software can rely on the field reading as all 1s.

  This description can apply to a single bit that reads as 1, or to a
  field that reads as all 1s.

Read-As-Zero (RAZ)
  Hardware must implement the field as reading as all 0s.

  Software can rely on the field reading as all 0s.

  This description can apply to a single bit that reads as 0, or to a
  field that reads as all 0s.

SBO
    See Should-Be-One (SBO).

SBOP
    See Should-Be-One-or-Preserved (SBOP).

SBZ
    See Should-Be-Zero (SBZ).

SBZP
    See Should-Be-Zero-or-Preserved (SBZP).

Should-Be-One (SBO)
  Hardware must ignore writes to the field.

  Software should write the field as all 1s.  If software writes a
  value that is not all 1s, it must expect an unpredictable result.

  This description can apply to a single bit that should be written as
  1, or to a field that should be written as all 1s.

Should-Be-One-or-Preserved (SBOP)
  The Large Physical Address Extension modifies the definition of SBOP
  for register bits that are reallocated by the extension, and as a
  result are SBOP in some but not all contexts.  For more information
  see the ARM Architecture Reference Manual, ARMv7-A and ARMv7-R
  edition.  The generic definition of SBOP given here applies only to
  bits that are not affected by this modification.

  Hardware must ignore writes to the field.

  If software has read the field since the processor implementing the
  field was last reset and initialized, it should preserve the value
  of the field by writing the value that it previously read from the
  field.  Otherwise, it should write the field as all 1s.

  If software writes a value to the field that is not a value
  previously read for the field and is not all 1s, it must expect an
  unpredictable result.

  This description can apply to a single bit that should be written as
  its preserved value or as 1, or to a field that should be written as
  its preserved value or as all 1s.

Should-Be-Zero (SBZ)
  Hardware must ignore writes to the field.

  Software should write the field as all 0s.  If software writes a
  value that is not all 0s, it must expect an unpredictable result.

  This description can apply to a single bit that should be written as
  0, or to a field that should be written as all 0s.

Should-Be-Zero-or-Preserved (SBZP)
  The Large Physical Address Extension modifies the definition of SBZP
  for register bits that are reallocated by the extension, and as a
  result are SBZP in some but not all contexts.  For more information
  see the ARM Architecture Reference Manual, ARMv7-A and ARMv7-R
  edition.  The generic definition of SBZP given here applies only to
  bits that are not affected by this modification.

  Hardware must ignore writes to the field.

  If software has read the field since the processor implementing the
  field was last reset and initialized, it must preserve the value of
  the field by writing the value that it previously read from the
  field.  Otherwise, it must write the field as all 0s.

  If software writes a value to the field that is not a value
  previously read for the field and is not all 0s, it must expect an
  unpredictable result.

  This description can apply to a single bit that should be written as
  its preserved value or as 0, or to a field that should be written as
  its preserved value or as all 0s.

UNK
  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.

UNK/SBOP
  Hardware must implement the field as Read-As-One, and must ignore
  writes to the field.

  Software must not rely on the field reading as all 1s, and except
  for writing back to the register it must treat the value as if it is
  unknown.  Software must use an SBOP policy to write to the field.

  This description can apply to a single bit that should be written as
  its preserved value or as 1, or to a field that should be written as
  its preserved value or as all 1s.

UNK/SBZP
  Hardware must implement the field as Read-As-Zero, and must ignore
  writes to the field.

  Software must not rely on the field reading as all 0s, and except
  for writing back to the register it must treat the value as if it is
  unknown.  Software must use an SBZP policy to write to the field.

  This description can apply to a single bit that should be written as
  its preserved value or as 0, or to a field that should be written as
  its preserved value or as all 0s.

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 or
  documented or promoted as having a defined value or effect.

  When unknown appears in body text, it is always in small capitals.