ARM > Introduction to ARM > Architecture 4

by David Thomas on —

Architecture 4

  • v4 is the oldest supported architecture today. It added:
    • Load/store instructions for signed and unsigned halfwords and bytes.
    • LDRH, LDRSH, LDRSB.
    • System mode – privileged mode using user registers.
    • 26-bit addressing no longer supported.
  • v4T added:
    • Thumb mode.

Remarks

This is the first architecture to have a full formal definition.

  • Ops which yielded PC+12 in earlier ARMs are declared UNPREDICTABLE.
  • Reserves some of the SWI space for architecturally-defined operations.