Arm-Bit-Banding

Implementation of the ARM bit-banding mechanism which exist in Cortex-M3 and Cortex-M4 CPUs.

Bit-banding maps a complete word of memory onto a single bit in the bit-band region. For example, writing to one of the alias words sets or clears the corresponding bit in the bit-band region. This enables every individual bit in the bit-banding region to be directly accessible from a word-aligned address using a single LDR instruction. It also enables individual bits to be toggled without performing a read-modify-write sequence of instructions.

The processor memory map includes two bit-band regions. These occupy the lowest 1MB of the SRAM and Peripheral memory regions respectively. These bit-band regions map each word in an alias region of memory to a bit in a bit-band region of memory.

Warning

In the current moment implement work only with SRAM bit-banding region.

Installation

For installation you need to do 2 simply steps:

• Copy necessary arm_bit_banding.h file to your project
• Include arm_bit_banding.h into your source code.

Also this library requires definition of SRAM1_BB_BASE - SRAM base address in the bit-band region and SRAM1_BASE - SRAM base address in the alias region. You need define it manually or include special header files provided by vendor. For example stm32f407xx.h from STM.

Usage

Current library define special data type flag_t for work with bit-banding memory region. This data type is implementing of ARM bit-banding mechanism. It stores the alias address calculated for corresponding bit in the bit-band region.

For usage this library you need make next steps:

1. Define uint8_t flags state variables which placed within SRAM bit-band region.

As flag variable you can use only uin8_t variables!

uint8_t state = 0;

2. Next you need to create flag_t variable for each necessary bit (flag) inside state variable:

flag_t error_flag = abb_make(&state, 3);
flag_t ready_flag = abb_make(&state, 6);

3. After this you can use this flag_t variables for atomic bit manipulation:

//Set bit
abb_set(error_flag);

//Clear bit
abb_clear(error_flag);

//Read bit
bool is_error = abb_tst(error_flag);