在STM的官方的固件库下面有个Examples里有个CortexM3文件夹，Example1给出了bitbanding详解的使用描述。
偏移用的基地址都是固定的
#define RAM_BASE 0x20000000
#define RAM_BB_BASE 0x22000000
三个对位操作的宏定义，清零、置位、读位：
#define Var_ResetBit_BB(VarAddr, BitNumber)
(*(vu32 *) (RAM_BB_BASE | ((VarAddr - RAM_BASE) << 5) | RAM_BB_BASE | ((BitNumber) << 2)) = 0)
#define Var_SetBit_BB(VarAddr, BitNumber)
(*(vu32 *) (RAM_BB_BASE | ((VarAddr - RAM_BASE) << 5) | RAM_BB_BASE | ((BitNumber) << 2)) = 1)
#define Var_GetBit_BB(VarAddr, BitNumber)
(*(vu32 *) (RAM_BB_BASE | ((VarAddr - RAM_BASE) << 5) | RAM_BB_BASE | ((BitNumber) << 2)))
使用方法：
/* A mapping formula shows how to reference each word in the alias region to a corresponding bit in the bit-band region. The mapping formula is:
bit_word_addr = bit_band_base + (byte_offset x 32) + (bit_number x4)
where:
- bit_word_addr: is the address of the word in the alias memory region that maps to the targeted bit.
- bit_band_base is the starting address of the alias region
- byte_offset is the number of the byte in the bit-band region that contains the targeted bit
- bit_number is the bit position (0-31) of the targeted bit */
/* Get the variable address --------------------------------------------------*/
VarAddr = (u32)&Var;
/* Modify variable bit using bit-band access ---------------------------------*/
/* Modify Var variable bit 0 -----------------------------------------------*/
Var_ResetBit_BB(VarAddr, 0); /* Var = 0x00005AA4 */
Var_SetBit_BB(VarAddr, 0); /* Var = 0x00005AA5 */
/* Modify Var variable bit 11 -----------------------------------------------*/
Var_ResetBit_BB(VarAddr, 11); /* Var = 0x000052A5 */
/* Get Var variable bit 11 value */
VarBitValue = Var_GetBit_BB(VarAddr, 11); /* VarBitValue = 0x00000000 */
Var_SetBit_BB(VarAddr, 11); /* Var = 0x00005AA5 */
/* Get Var variable bit 11 value */
VarBitValue = Var_GetBit_BB(VarAddr, 11); /* VarBitValue = 0x00000001 */
/* Modify Var variable bit 31 -----------------------------------------------*/
Var_SetBit_BB(VarAddr, 31); /* Var = 0x80005AA5 */
/* Get Var variable bit 31 value */
VarBitValue = Var_GetBit_BB(VarAddr, 31); /* VarBitValue = 0x00000001 */
Var_ResetBit_BB(VarAddr, 31); /* Var = 0x00005AA5 */
/* Get Var variable bit 31 value */
VarBitValue = Var_GetBit_BB(VarAddr, 31); /* VarBitValue = 0x00000000 */
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