ARM Compiler toolchain v4.1 for µVision Using the Compiler

Compiler Features
4.16 Compiler type attribute, __attribute__((bitband))
__attribute__((bitband)) is a type attribute that is used to bit-band type definitions of
structures.
In Example 4-7, the unplaced bit-banded objects must be relocated into the bit-band region. This
can be achieved by either using an appropriate scatter-loading description file or by using the
--rw_base linker command-line option.
Example 4-7 Unplaced object
/* foo.c */
typedef struct {
int i : 1;
int j : 2;
int k : 3;
} BB __attribute__((bitband));
BB value; // Unplaced object
void update_value(void)
{
value.i = 1;
value.j = 0;
}
/* end of foo.c */
Alternatively, __attribute__((at())) can be used to place bit-banded objects at a particular
address in the bit-band region. See Example 4-8.
Example 4-8 Placed object
/* foo.c */
typedef struct {
int i : 1;
int j : 2;
int k : 3;
} BB __attribute((bitband));
BB value __attribute__((at(0x20000040))); // Placed object
void update_value(void)
{
value.i = 1;
value.j = 0;
}
/* end of foo.c */
4.16.1 See also
Concepts
• Compiler and processor support for bit-banding on page 4-21.
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