Sub: add an external pressure failsafe #32090
Description
Feature request
Is your feature request related to a problem? Please describe.
If a vehicle goes too deep (e.g. beyond its component depth ratings), it can implode / get destroyed under the pressure. We don't currently have a means of directly warning about this before it starts happening.
Describe the solution you'd like
Make a dedicated external pressure failsafe, which monitors a baro specified as BARO_TYPE_WATER. That keeps setup, defaults, and user intuition simple, at the cost of some ambiguity around what to do if there is more than one water baro available (I vote just check the primary baro, and use it for the failsafe if it is a water baro).
Ideally it would be a multi-level failsafe, with low and critical depths specified (like with battery voltage). I believe the most logical supported actions are "Warn only", and "Surface", but "Depth hold" could potentially be an option in between 🤷♂️ .
Describe alternatives you've considered
We could alternatively expand the current internal pressure failsafe to more generally provide failsafes for each available barometer (similar to the battery failsafes, which exist per battery). That's more complex to set up because you need to know how many internal baros there are, but it does provide more control if that happens to be desired.
Platform
[ ] All
[ ] AntennaTracker
[ ] Copter
[ ] Plane
[ ] Rover
[X] Submarine
Additional context
The existing leak failsafe and internal pressure failsafe can potentially provide some warning of an imminent implosion as the enclosure starts to flex and/or leak, but that's much less comforting than being preemptively warned when close to component ratings.