[BUG] Seems Pin's set_low method implementation has tiny differents with GPIO_XXXX from C language

[AlexiaChen]

Rust version of this project:

  #[inline(always)]
    fn _set_high(&mut self) {
        // NOTE(unsafe) atomic write to a stateless register
        unsafe { (*Gpio::<P>::ptr()).bsrr.write(|w| w.bits(1 << N)) }
    }

    #[inline(always)]
    fn _set_low(&mut self) {
        // NOTE(unsafe) atomic write to a stateless register
        unsafe { (*Gpio::<P>::ptr()).bsrr.write(|w| w.bits(1 << (16 + N))) }
    }

I found whatever state of the pin, it will write GPIO BSRR resgiter。 But C project with Keil, I Found three methods that are different from your project, you can find it only writes BSRR when set high and only write BRR when set_low

/**
  * @brief  Sets the selected data port bits.
  * @param  GPIOx: where x can be (A..G) to select the GPIO peripheral.
  * @param  GPIO_Pin: specifies the port bits to be written.
  *   This parameter can be any combination of GPIO_Pin_x where x can be (0..15).
  * @retval None
  */
void GPIO_SetBits(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin)
{
  /* Check the parameters */
  assert_param(IS_GPIO_ALL_PERIPH(GPIOx));
  assert_param(IS_GPIO_PIN(GPIO_Pin));

  GPIOx->BSRR = GPIO_Pin;
}

/**
  * @brief  Clears the selected data port bits.
  * @param  GPIOx: where x can be (A..G) to select the GPIO peripheral.
  * @param  GPIO_Pin: specifies the port bits to be written.
  *   This parameter can be any combination of GPIO_Pin_x where x can be (0..15).
  * @retval None
  */
void GPIO_ResetBits(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin)
{
  /* Check the parameters */
  assert_param(IS_GPIO_ALL_PERIPH(GPIOx));
  assert_param(IS_GPIO_PIN(GPIO_Pin));

  GPIOx->BRR = GPIO_Pin;
}

it same as with the two methods I mentioned above. When BitAction is Reset ( set_low ), it will write BRR, not BSRR. when BitAction is not RESET(set_high), it will write BSRR

/**
  * @brief  Sets or clears the selected data port bit.
  * @param  GPIOx: where x can be (A..G) to select the GPIO peripheral.
  * @param  GPIO_Pin: specifies the port bit to be written.
  *   This parameter can be one of GPIO_Pin_x where x can be (0..15).
  * @param  BitVal: specifies the value to be written to the selected bit.
  *   This parameter can be one of the BitAction enum values:
  *     @arg Bit_RESET: to clear the port pin
  *     @arg Bit_SET: to set the port pin
  * @retval None
  */
void GPIO_WriteBit(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin, BitAction BitVal)
{
  /* Check the parameters */
  assert_param(IS_GPIO_ALL_PERIPH(GPIOx));
  assert_param(IS_GET_GPIO_PIN(GPIO_Pin));
  assert_param(IS_GPIO_BIT_ACTION(BitVal)); 

  if (BitVal != Bit_RESET)
  {
    GPIOx->BSRR = GPIO_Pin;
  }
  else
  {
    GPIOx->BRR = GPIO_Pin;
  }
}

your project impl Pin's set_low underlayer logic might has some issues， they are different with C language implementation。

[AlexiaChen]

There is no bug, my fault. BSRR can do reset