Callback fuzziness???

[srogers]

I am trying to understand the meaning of the following 'tip' for the building of interrupt handling code. The following tip can be found at:

https://docs.micropython.org/en/latest/ ... rules.html

• Where an ISR returns multiple bytes use a pre-allocated bytearray. If multiple integers are to be shared between an ISR and the main program consider an array (array.array).

When I looked at how to set up an interrupt handler (for a Timer class),I've seen examples like this:

Code: Select all

# -----------------------------------------
def mycallback(t):
    pass.

tim = machine.Timer()
tim.init(mode = Timer.PERIODIC, period = 1000, callback = mycallback)
# -----------------------------------------------

What I do not understand is how does a callback (interrupt handler) like mycallback(t) above return anything, much less a pre-allocated buffer?

Did the hint mean to say something other than return'? Did the hint mean to say that the ISR should update a pre-allocated memory buffer like a pre-allocated bytearray or a pre-allocated array.array? If this is not the case, how does one construct an ISR that 'returns' a pre-allocated buffer with the 'return' reserved word, and how does it get passed back via the callback function return?

[fivdi]

Did the hint mean to say something other than return'?

I guess the word return is overloaded. In the context of an ISR the returned data doesn't mean the value sent back to the ISR caller with a return statement. It means the data that the ISR knows about that it needs to share with (or return to) the main program.

Did the hint mean to say that the ISR should update a pre-allocated memory buffer like a pre-allocated bytearray or a pre-allocated array.array?

Yes, this is what it means.

The "Writing interrupt handlers" documentation has a section titled Critical sections showing how this can be done.