Simple Maths results in Guru Meditation Error

[iamastic]

Hi,

I am working with the NodeMCU ESP32. I have a coin sensor built from two copper plates that detect when a coin rolls down the chute. I am using the interrupt function to detect the coin. It works well with the Arduino Uno R3, but when connected to the NodeMCU ESP32, a simple calculation in my function results in the following error:

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Guru Meditation Error: Core 1 panic'ed (Coprocessor exception)

It goes on to show me the Core 1 register dump, and then says:

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Core 1 was running in ISR context

Here is the breakdown of the code I am using:

1) I set up the interrupt on GPIO 17:

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attachInterrupt( digitalPinToInterrupt(INPUT_PIN_COIN), Interrupt_CoinDeposit, FALLING );

2) The Interrupt_CoinDeposit() calls another function:

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void IRAM_ATTR Interrupt_CoinDeposit()
{
    g_crOSCore.EnqueueCoin();
}

3) The Enqueue Coin function is supposed to check if one second has passed since the first time the coin struck the copper plates. This is to avoid the same coin being counted multiple times due to contact bounce:

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bool CCrowboxCore::EnqueueCoin()              
{
    //cros_time_t is a typedef of float
    cros_time_t n = GetUptimeSeconds();
    Serial.println(n);

    cros_time_t m = m_uptimeLastCoinDetected;
    Serial.println(m);

    cros_time_t x = n - m;
    Serial.println(x);

   if (x < 1.0) {      
      return false;
    }
  
    m_numEnqueuedDeposits++;    
    m_uptimeLastCoinDetected = GetUptimeSeconds();
    return true;
}

Notes:

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GetUptimeSeconds();

is a function that returns the time, in type float, that the NodeMCU has been running.

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m_uptimeLastCoinDetected

is another float that has been initiated in the setup() function.

My code runs into issues when I reach the

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x = n - m

line. I have tested this by using print lines as well as commenting out sections of the code. This code works with the Arduino Uno R3 but I can't seem to figure out why I am getting a segmentation fault with the ESP32.

[ESP_Sprite]

You're trying to do floating point math in an interrupt handler. Don't do that.

[iamastic]

I see, that's interesting! Do you know why that is? Is it specific to the ESP32 only? Because it appears to work on the Arduino Uno R3 / atmega328p.

I will try converting to an integer then instead and see if that works. Thanks!

[ESP_Sprite]

It has something to do with the fact that floating point numbers in the ESP32 are accelerated by a FPU that has registers that need to be saved and loaded every time there is a task switch, which is kind-of expensive in processing terms. That takes time and floating point numbers are generally only used in one or two tasks in an embedded system, so FreeRTOS uses a smart trick to only load and save those registers when needed. The logic used for that doesn't work in an interrupt, though, hence the exception. An Arduino Uno has no such hardware, so doesn't need logic like that.