ARM Cortex R4F - Manual (Page 51)

Programmer’s Model
ARM DDI 0363E Copyright © 2009 ARM Limited. All rights reserved. 2-5
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2.4 Data types
The processor supports these data types:
•
doubleword, 64-bit
• word, 32-bit
• halfword, 16-bit
• byte, 8-bit.
Note
• 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.
Note
You cannot use LDRD , LDM , STRD , or STM instructions to access 32-bit quantities if they are not
32-bit aligned.