Bit-banding Alternatives for Modern ARM Cores

[Komal_Y]

Bit-banding Alternatives for Modern ARM Cores

Background Information:

The bit-banding feature available in ARM Cortex-M cores (ARMv7-M architecture including Cortex-M3 and Cortex-M4) provides hardware-level mapping of individual bits within a 1 MB memory region to words in a 32 MB alias region. This mechanism enables atomic bit manipulation without requiring read-modify-write operations.

Specific Query:

For ARM Cortex cores beyond M7 architecture that do not support the bit-banding feature, could you please provide detailed information regarding:

• Available alternative methods for atomic bit manipulation
• Performance implications of these alternatives
• Recommended implementation strategies for maintaining atomic operations
• Code examples demonstrating these alternative approaches
• Request for Documentation

[mƎALLEm]

Hello,

Indeed bit-banding is not available on Cortex-M7. According to ARM community from this post, the reason is the following:

Regarding an available alternative, I think the only solution is to use CMSIS:

void atomic_set_bit(volatile uint32_t *addr, uint32_t bit) {
    uint32_t old, status;
    do {
        old = __LDREXW(addr);
        old |= (1U << bit);
        status = __STREXW(old, addr);
    } while (status != 0);
}

Use __LDREXW/__STREXW for 32-bit, __LDREXH/__STREXH for 16-bit, and __LDREXB/__STREXB for 8-bit operations.

I don't think there is specific documentation regarding this subject

[Andrew Neil]

---

@Komal_Y wrote:

• Available alternative methods for atomic bit manipulation

---

Check if your particular chip has a register (or registers) to give atomic bit manipulation; eg,

That's for STM32H723/733, STM32H725/735 and STM32H730:

https://www.st.com/resource/en/reference_manual/rm0468-stm32h723733-stm32h725735-and-stm32h730-value-line-advanced-armbased-32bit-mcus-stmicroelectronics.pdf#page=521

PS:

You'll probably find that HAL uses this - it certainly does for F0.