Using the ODR register directly On STM32

Question

Modify the code for WriteLED() to use the ODR register directly. The code should read the current value of the register and then write back a modified value depending on what LEDs are to be turns on or off.

Example Code Given to me

void HAL_GPIO_TogglePin(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin)
{
/* Check the parameters */
assert_param(IS_GPIO_PIN(GPIO_Pin));
GPIOx->ODR ˆ= GPIO_Pin;
}

Code That Needs to be Altered

WriteLED (uint8_t LED, uint8_t State)
{
  // Check for correct state
 if ((State != LED_OFF) && (State != LED_ON))
  {
    return;
  }

  // Turn on/off the LED
  switch (LED)
    {
    case 'L':
      HAL_GPIO_WritePin (LD4_GPIO_Port, LD4_Pin, State);
      break;
    case 'T':
      HAL_GPIO_WritePin (LD3_GPIO_Port, LD3_Pin, State);
      break;
    case 'B':
      HAL_GPIO_WritePin (LD6_GPIO_Port, LD6_Pin, State);
      break;
    case 'R':
      HAL_GPIO_WritePin (LD5_GPIO_Port, LD5_Pin, State);
      break;
    }

  return;
}

What should the above code look like when outputting to ODR register

Answer 1

You need to understand C bitwise operations. The three are ^ (exclusive OR), & (bitwise and), | (bitwise or)

To clear a bit GPIO->ODR &= ~pin_mask;

To set a bit GPIO->ODR |= pin_mask;

This should give you enough information.