GPIO HAL Sanity Check

[Carl_G]

I need a second pair of eyes. I am trying to setup EXTI using the GPIO HAL. But it looks like its doing it wrong. It must be me but I need you to double check to be sure.

This is STM32G0 HAL so stm32g0xx_hal_gpio.c

/*--------------------- EXTI Mode Configuration ------------------------*/
      /* Configure the External Interrupt or event for the current IO */
      if ((GPIO_Init->Mode & EXTI_MODE) != 0x00u)
      {
        temp = EXTI->EXTICR[position >> 2u];
        temp &= ~(0x0FuL << (8u * (position & 0x03u)));
        temp |= (GPIO_GET_INDEX(GPIOx) << (8u * (position & 0x03u)));
        EXTI->EXTICR[position >> 2u] = temp;

In this code sample the macro GPIO_GET_INDEX is used. It takes the value "GPIO_TypeDef *GPIOx" and this value will enter the function as  GPIOB, GPIOA etc. The macro is 

#if defined(GPIOE)   
#define GPIO_GET_INDEX(__GPIOx__)    (((__GPIOx__) == (GPIOA))? 0uL :\
                                      ((__GPIOx__) == (GPIOB))? 1uL :\
                                      ((__GPIOx__) == (GPIOC))? 2uL :\
                                      ((__GPIOx__) == (GPIOD))? 3uL :\
                                      ((__GPIOx__) == (GPIOE))? 4uL : 5uL)
#else
#define GPIO_GET_INDEX(__GPIOx__)    (((__GPIOx__) == (GPIOA))? 0uL :\
                                      ((__GPIOx__) == (GPIOB))? 1uL :\
                                      ((__GPIOx__) == (GPIOC))? 2uL :\
                                      ((__GPIOx__) == (GPIOD))? 3uL : 5uL)
#endif /* GPIOE */

There is no GPIOE so the second macro. The problem is if you pass in GPIOA you get a 0. 0s don't shift. So the statement 

temp |= (GPIO_GET_INDEX(GPIOx) << (8u * (position & 0x03u)));

Will always result in a 0 for GPIOA. Which means EXTI is never setup for GPIOA. But even worse, GPIOB is also 1 position off. It seems this statement requires something indexed to 1 and not to 0. It is the result I am getting in my software. EXTI is not being setup correctly when I do this.

Am I misreading it??

[TDK]

GPIOA is selected when the field is zero, GPIOB is 1, etc. The statement before clears the field. Seems correct. Look at the description of exticr in the reference manual.

[Carl_G]

Spoiler

I guess i was confused because the reference manual says "these bits are written" implying its bitwise. But with PD being 3 it can't be bitwise.  This implies only one of any given numbered port can trigger an interrupt or be a wakeup. So either PA6 or PB6 or PC6 but only one of them. No one has ever mentioned this in their lessons or videos...

This is a bit strange though isn't it? If its not bitwise why the &=~ and the |=  Why even care about the previous value if its not bitwise?