Introduction to ARM

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.

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