How does the HAL/LL function LL_GPIO_SetPinMode() work?

[Kmax18]

Ok, I scratched my head long enough and now my hope lies with the ST Community. =)

I would like to understand how this code in the header file stm32f1xx_ll_gpio.h works. In particular, what does (Pin >> 24) do? I suspect that the code sets two registers: GPIOx_BSRR and GPIOx_CRL. Here:

Pin = LL_GPIO_PIN_5

GPIOx = GPIOC

Thank you.

__STATIC_INLINE void LL_GPIO_SetPinMode(GPIO_TypeDef *GPIOx, uint32_t Pin, uint32_t Mode)

{

 register uint32_t *pReg = (uint32_t *)((uint32_t)(&GPIOx->CRL) + (Pin >> 24));

 MODIFY_REG(*pReg, ((GPIO_CRL_CNF0 | GPIO_CRL_MODE0) << (POSITION_VAL(Pin) * 4U)),

Mode << (POSITION_VAL(Pin) * 4U)));

}

[TDK · Accepted solution]

The 26th bit is 1 for pins 8 and higher which makes the code set pReg to point to GPIOx->CRH rather than GPIOx->CRL.

#define LL_GPIO_PIN_0                    ((GPIO_BSRR_BS0  << GPIO_PIN_MASK_POS) | 0x00000001U)  /*!< Select pin 0  */
#define LL_GPIO_PIN_1                    ((GPIO_BSRR_BS1  << GPIO_PIN_MASK_POS) | 0x00000002U)  /*!< Select pin 1  */
#define LL_GPIO_PIN_2                    ((GPIO_BSRR_BS2  << GPIO_PIN_MASK_POS) | 0x00000004U)  /*!< Select pin 2  */
#define LL_GPIO_PIN_3                    ((GPIO_BSRR_BS3  << GPIO_PIN_MASK_POS) | 0x00000008U)  /*!< Select pin 3  */
#define LL_GPIO_PIN_4                    ((GPIO_BSRR_BS4  << GPIO_PIN_MASK_POS) | 0x00000010U)  /*!< Select pin 4  */
#define LL_GPIO_PIN_5                    ((GPIO_BSRR_BS5  << GPIO_PIN_MASK_POS) | 0x00000020U)  /*!< Select pin 5  */
#define LL_GPIO_PIN_6                    ((GPIO_BSRR_BS6  << GPIO_PIN_MASK_POS) | 0x00000040U)  /*!< Select pin 6  */
#define LL_GPIO_PIN_7                    ((GPIO_BSRR_BS7  << GPIO_PIN_MASK_POS) | 0x00000080U)  /*!< Select pin 7  */
#define LL_GPIO_PIN_8                    ((GPIO_BSRR_BS8  << GPIO_PIN_MASK_POS) | 0x04000001U)  /*!< Select pin 8  */
#define LL_GPIO_PIN_9                    ((GPIO_BSRR_BS9  << GPIO_PIN_MASK_POS) | 0x04000002U)  /*!< Select pin 9  */
#define LL_GPIO_PIN_10                   ((GPIO_BSRR_BS10 << GPIO_PIN_MASK_POS) | 0x04000004U)  /*!< Select pin 10 */
#define LL_GPIO_PIN_11                   ((GPIO_BSRR_BS11 << GPIO_PIN_MASK_POS) | 0x04000008U)  /*!< Select pin 11 */
#define LL_GPIO_PIN_12                   ((GPIO_BSRR_BS12 << GPIO_PIN_MASK_POS) | 0x04000010U)  /*!< Select pin 12 */
#define LL_GPIO_PIN_13                   ((GPIO_BSRR_BS13 << GPIO_PIN_MASK_POS) | 0x04000020U)  /*!< Select pin 13 */
#define LL_GPIO_PIN_14                   ((GPIO_BSRR_BS14 << GPIO_PIN_MASK_POS) | 0x04000040U)  /*!< Select pin 14 */
#define LL_GPIO_PIN_15                   ((GPIO_BSRR_BS15 << GPIO_PIN_MASK_POS) | 0x04000080U)  /*!< Select pin 15 */

[Kmax18]

Thank you for your response. Would it not be easier to point to point to GPIOx->CRH instead of manipulating the register address? What is the motivation for the algorithm?

[TDK]

Pointing to CRH doesnt help if half the pins need CRL and the other half need CRH. There are other ways to implement it but this one seems okay if a bit obfuscated.
Of note, doing shifts to implement this rather than conditional if statements allows instructions to be streamlined, not that it matters much for the M0 core.