Arm Cortex R4F Bedienungsanleitung Seite 51

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Programmer’s Model
ARM DDI 0363E Copyright © 2009 ARM Limited. All rights reserved. 2-5
ID013010 Non-Confidential, Unrestricted Access
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.
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