The --bitband command-line option bit-bands all non const global structure objects.

When --bitband is applied to foo.c in Example 30, 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.

/* 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 31, the access to rts is bit-banded.

/* 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 */