Bugfix: 'on_get_cb': return value was swallowed

[hmaerki]

Bug

• If on_get_cb is defined, the second call to self._create_response() overwrites the value returned by on_get_cb.
• In other words: The value set by on_get_cb was swallowed.

Bugfix

• Simplified code
• Call self._create_response() only once.

[GimmickNG]

I think I did something like this earlier as well. The problem is that caching it this way means that on_get_cb also has no chance to update the vals the way it's implemented now -- so the tests where it calls set_ireg in the on_get_cb might fail, since it expects the register values to update after it is called - but it would end up returning the old value instead of the new one.

[hmaerki]

I think I did something like this earlier as well. The problem is that caching it this way means that on_get_cb also has no chance to update the vals the way it's implemented now -- so the tests where it calls set_ireg in the on_get_cb might fail, since it expects the register values to update after it is called - but it would end up returning the old value instead of the new one.

Hi @GimmickNG Thanks for your feedback. I could not follow your explanation as I do not know the library sufficiently. I was struggling due to lack of documentation or lack of examples (or I did just missed important parts).

Reading the documentation/examples, I failed to understand how to implement these concepts:

• Set synchron (set a value in a 'on_set_cb').
• Set asynchron (No 'on_set_cb'. Read the value from 'micropython-modbus' when it is needed)
• Get synchron (In 'on_get_cb', get the the value, lets say from a sensor, and update it) (This does not work - see this PR)
• Get asynchron: (No 'on_set_cb'. Ppoll for the sensor value and update the value stored in 'micropython-modbus'.)

Eventually, the developer has to decide between these two concepts

• The state(value) should be maintained by 'micropython-modbus': Then use Set/Get asynchron.
• The state (value) is maintained outside of 'micropython-modbus', for example in the sensor/actor. Then use Set/Get synchron.

It might be helpful to have the documentation and examples structured this way.

If you like, I could spend some hours in creating

• Proposal for update to the documentation
• Proposal for 4 examples as described above