> Is it generally ok to have about 30 lines of code inside the interrupt
> routine?

Stephen, hi, you can have as many lines of code as you like inside
an ISR. The only proviso is that, generally, if you are expecting
another interrupt, the current interrupt processing is finished. Or
at least left in a state that you can return to if, for example, a higher
priority or other interrupt/event needs processing first

If an interrupting source is re-enabled before ISR completion then
it's possible to interrupt back into an uncompleted ISR. In that
case you'd have to look at something like POPping the stack

For example, if you had only one interrupt, say a 1 second timer
IRQ, then you could have code inside the ISR that took almost 1
second to complete. And that's a lot of code execution time

I think what most people would do is make the ISR short and, if
possible or necessary, pass information from the ISR to the main
loop. But there's nothing to say that an ISR can't be an entity in
itself which completes a task without help from the main loop

However, apart from the h/w side of things, which is important of
course, an ISR is basically only a sub-routine. The question is not
what happens inside the ISR, it's the overall s/w flow management.
You, the coder, are in charge, not the chip

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