fix(a32nx/fcu) Fixed FCU ALT selector immediately switching to 1000s when interval selected

[elliot747]

Fixes #9699

Summary of Changes

Updated FcuComputer.cpp so that it doesn't run the code if number of turns of the ALT knob are 0 (which is the case where the increment knob is turned). Also had to add logic so that if the currently selected altitude is in hundreds (interval=1000ft), when the ALT knob is moved it doesn't jump by more than 1000ft - e.g. the code would have gone from 6300ft straight to 5000ft when dialling the altitude down with the previous version of the code as round(6300ft - 1000ft) = 5000ft - but we just want 6300ft to go to 6000ft on the first turn of the knob.

Screenshots (if necessary)

References

Behaviour observed on IRL aircraft

Additional context

First time contributing to an opensource project - so I hope I've followed the process right, but I was software engineer at Thales before my 320 TR flying for about 5 years now so hopefully I can contribute a little more going forward.

Discord username (if different from GitHub):

Testing instructions

Select an altitude in 100s of feet. Change the interval selector to 1000s of feet. Note the selected altitude doesn't change, it remains in 100s of feet.
Select an altitude with 100s of feet between 100 and 400ft. Change the interval selector to 1000s of feet. Turn the ALT selector knob to increase altitude, observe it increases the altitude to the next thousand. Repeat, but turn the ALT selector knob to decrease altitude, observe the altitude is just rounded down.
Select an altitude with 100s of feet between 600 and 900ft. Change the interval selector to 1000s of feet. Turn the ALT selector knob to increase altitude, observe it increases the altitude to the next thousand. Repeat, but turn the ALT selector knob to decrease altitude, observe the altitude is rounded down.
Select an altitude with 100s of feet with 500ft (e.g. 1500ft). Change the interval selector to 1000s of feet. Turn the ALT selector knob to increase altitude, observe it increases the altitude to the next thousand. Repeat, but turn the ALT selector knob to decrease altitude, observe the altitude is rounded down.
General testing of other altitude selection behaviour, also check that the minimum selection of 100ft and maximum of 49000ft has been unaffected.

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[alepouna]

Thank you for the contribution 🙌