ARM R4 Manuale Utente

ARM DDI 0363E

2-5

ID013010

The processor supports these data types:
•

doubleword, 64-bit

•

word, 32-bit

•

halfword, 16-bit

•

byte, 8-bit.

 •

When any of these types are described as unsigned, the N-bit data value represents a 
non-negative integer in the range 0 to +2

N

-1, using normal binary format.

•

When any of these types are described as signed, the N-bit data value represents an integer 
in the range -2

N-1

 to +2

N-1

-1, using two’s complement format.

For best performance you must align these data types in memory as follows:
•

doubleword quantities aligned to 8-byte boundaries, doubleword aligned

•

word quantities aligned to 4-byte boundaries, word aligned

•

halfword quantities aligned to 2-byte boundaries halfword aligned

•

byte quantities can be placed on any byte boundary.

The processor supports mixed-endian and unaligned access. For more information, see 
Unaligned and mixed-endian data access support on page 2-28.

 You  cannot  use 

LDRD

, 

LDM

, 

STRD

, or 

STM

 instructions to access 32-bit quantities if they are not 

32-bit aligned.