Post History

Error handling in embedded systems

How do I handle errors in my embedded system? I have learned that it is a de facto standard for driver functions to return an error code that reveals if the function fulfilled its main purpose or if it encountered an error. If we take a look at the switch-case construct in [Lundin's state machine](https://electrical.codidact.com/posts/295939) for a coffee machine, we see that a special function `error_handler()` is called and takes the error code as input argument if the result is `COFFEE_NO_WATER`.

```C
#include <stdio.h>
int main()
{
  static coffee_state_t state = COFFEE_SCAN_BUTTONS;
  coffee_result_t result;

  for(;;)
  {
    result = state_machine[state]();
    state = evaluate_result(state, result);
  }
}

static coffee_state_t evaluate_result (coffee_state_t  current_state,
                                       coffee_result_t result)
{
  // stay in the same state as default behavior:
  coffee_state_t next_state = current_state;

  switch(current_state)
  {
    case COFFEE_MIX_WATER:
    {
      if(result == COFFEE_NO_WATER)
      {
        next_state = COFFEE_MAINTENANCE;
        error_handler(COFFEE_NO_WATER);
      }
      break;
    }
  }

  return next_state;
}

static void error_handler (coffee_result_t error_code)
{
  // do something meaningful here based on error code
  (void)error_code;
}
```

My question is, what is `error_handler()` supposed to do? What does its innards look like? Is its purpose to make visible to the user/programmer which errors has happened? Or is its purpose something else?

To this end, I might add that I have understood that there are at least two kinds of errors - "soft errors" and "hard errors". A soft error could be that an opcode is received correctly via UART, but it is an operation that our microcontroller program does not recognize/support. Since the UART connection is still intact we can send a message to the other end (which might be a PC) stating what went wrong, giving a clear indication that an error happened.

A hard error could be that the UART connection disconnects or that baud rates are not correctly configured. In such instances, how should the error be handled?