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Compiler-specific Features
BB bb __attribute__((at(0x20000004)));
void foo(void)
{
bb.i = 1;
}
For peripherals that are width-sensitive, byte, halfword, and word stores or loads to the
alias space are generated for char, short, and int types of bitfields of bit-banded structs
respectively.
In Example 4-7 bit-banded access is generated for bb.i.
Example 4-7 Bitfield bit-band access
typedef struct {
char i: 1;
int j: 2;
int k: 3;
} BB __attribute__((bitband));
BB bb __attribute__((at(0x20000004)));
void foo()
{
bb.i = 1;
}
If you do not use __attribute__((at())) to place the bit-banded variable in the bit-band
region then you must relocate it using another method. You can do this by either using
an appropriate scatter-loading description file or by using the --rw_base linker
command-line option. See the Linker Reference Guide for more information.
Restrictions
The following restrictions apply:
• This type attribute can only be used with struct. Any union type or other
aggregate type with a union as a member cannot be bit-banded.
• Members of structs cannot be bit-banded individually.
• Bit-banded accesses are generated only for single-bit bitfields.
4-44 Copyright © 2007-2010 ARM. All rights reserved. ARM DUI 0348C
Non-Confidential,
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