ARM Compiler toolchain v4.1 for µVision Using the Compiler

Compiler Features
4.17 --bitband compiler command-line option
The --bitband command-line option bit-bands all non const global structure objects.
When --bitband is applied to foo.c in Example 4-9, the write to value.i is bit-banded. That is,
the value 0x00000001 is written to the bit-band alias word that value.i maps to in the bit-band
region.
Accesses to value.j and value.k are not bit-banded.
Example 4-9 Using the --bitband command-line option
/* foo.c */
typedef struct {
int i : 1;
int j : 2;
int k : 3;
} BB;
BB value __attribute__((at(0x20000040))); // Placed object
void update_value(void)
{
value.i = 1;
value.j = 0;
}
/* end of foo.c */
armcc supports the bit-banding of objects accessed through absolute addresses. When --bitband
is applied to foo.c in Example 4-10, the access to rts is bit-banded.
Example 4-10 Bit-banding of objects accessed through absolute addresses
/* foo.c */
typedef struct {
int rts : 1;
int cts : 1;
unsigned int data;
} uart;
#define com2 (*((volatile uart *)0x20002000))
void put_com2(int n)
{
com2.rts = 1;
com2.data = n;
}
/* end of foo.c */
4.17.1 See also
Concepts
• Compiler and processor support for bit-banding on page 4-21.
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