What is this: Unhandled exception in interrupt handler TypeError: 'str' object is not callable

[constantinos]

It occures when an interrupt is triggered after a Timer.Alarm invoked for the first time.
The code running inside the ISR handler is something like P += 1.

Any help is appreciated.
Constantinos

[robert-hh]

Do you have more insight to your code, especially the statement where yoe set up the timer alarm and the interrupt handler itself?

[constantinos]

@robert-hh Maybe I found the problem. I was initializing the callback handler for the Pin inside a class. The call back method was a class method. I realized that callback handlers must be single functions.

[robert-hh]

No, the callback handler can be inside a class. But then the handler must have self as first additional argument. Example (ESP8266 one, but principle should work) with ISR fucntion sample.

class acquire:

    def __init__(self):
        self.adc_read = machine.ADC(0).read
        self.data = array.array("L", [0] * _BUFFERSIZE)
        self.index_put = 0

    def sample(self, x):
        self.data[self.index_put] = self.adc_read()
        self.index_put = (self.index_put + 1) % _BUFFERSIZE
        self.irq_busy = False