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Compiler-specific Features
4.4 Type attributes
The __attribute__ keyword enables you to specify special attributes of variables or
structure fields, functions, and types. The keyword format is either:
__attribute__ ((attribute1, attribute2, ...))
__attribute__ ((__attribute1__, __attribute2__, ...))
For example:
void * Function_Attributes_malloc_0(int b) __attribute__ ((malloc));
static int b __attribute__ ((__unused__));
Table 4-4 summarizes the available type attributes.
Table 4-4 Type attributes supported by the compiler and their equivalents
Type attribute
non-attribute equivalent
__attribute__((bitband)) -
__attribute__((aligned))
__attribute__((packed))
__align
__packed a
__attribute__((transparent_union)) -
a. The __packed qualifier does not affect type in GNU mode.
4.4.1 __attribute__((bitband))
__attribute__((bitband)) is a type attribute that gives you efficient atomic access to
single-bit values in SRAM and Peripheral regions of the memory architecture. It is
possible to set or clear a single bit directly with a single memory access in certain
memory regions, rather than having to use the traditional read, modify, write approach.
It is also possible to read a single bit directly rather than having to use the traditional
read then shift and mask operation. Example 4-6 illustrates the use of
__attribute__((bitband)).
Example 4-6 Using __attribute__((bitband))
typedef struct {
int i: 1;
int j: 2;
int k: 3;
} BB __attribute__((bitband));
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