deco code rewrite

[Jan Schubert]

On 12/06/12 16:15, Dirk Hohndel wrote:
> On Dec 6, 2012, at 4:59 AM, Jef Driesen wrote:
>
>> On 2012-12-05 23:47, Dirk Hohndel wrote:
>>> Fundamentally we are of course missing CC support (as that was a
>>> rebreather dive, correct?). That is something that you and I should
>>> discuss in more detail to understand how we should add this to
>>> Subsurface.
>> Keep me CC'ed on that discussion!
> I think I'll do that here on the list so everyone gets to see it…
>
> From my discussions with Jan so far I think the first thing that we will need is the setpoints from the dive computer. This is basically the setting that tells the us what the "constant pO2" is that the diver is diving with. Depending on the model of dive computer there are either a number of pre-defined setpoints (that's what the OSTC does) or they can be changed in increments during the dive (Shearwater).
>
> If we get those and the gas mix of the dilutant we can do correct partial pressure graphs (and can do deco calculations, once that code has been added).
>
> So maybe this is something we could still add for libdivecomputer 0.3? I think the easiest way to extend the current libdivecomputer design to deal with this is to model these as events:
>
> if the diver is in CC mode (or enters CC mode), then send a DC_EVENT_SETPOINT on the first sample that gives us the current setpoint.
> if the dive computer reports a change in setpoint, then send another DC_EVENT_SETPOINT event.
> value should simply be the pO2 (since the current design uses floating point we can simply use a double with the correct value)
>
> Does that work?
>
> Jan, is there something else we need to add right now?

OK, from a users point of view we just need to know if a dive (or parts
of it) has been OC or CC. Using DC_EVENT_SETPOINT is just half way
through as in real life the setpoint is not constant. Depending on the
type of the (C)CR the real pO2 will fluctuate, drift and spike. Also the
pO2 can vary in quite huge ways when the user decides to manually
(over)steer the unit, flashes the loop, there is an accident, or some
other issues. My hardwired Predator will record the real pO2 and report
it when dowloading the log. There are other Computers which are not
connected to the unit (including OSTC and unwired Predators, Pretels)
but just use predefined set points for deco calculation. In case we get
real pO2 data we should use them of course. In this case there would
even be no strong need to know the real set point but would be nice and
will be reported anyway. In all other cases subsurface should just use a
constant pO2, the same as the defined set point.

Please note: All of the above is not valid anymore when it comes to
pSCR, we only address [e|m|h|whatever]CCR with this. But as pSCR uses
pSCR because they not trust any electronics and do not even use dive
computers at all there is no need to cover this topic for a dive
computer software (whoa, seeing some complains coming now :-).

Personaly I use a hardwired Predator (meaning reading all my thre O2
cells, calculating the pO2 from this and steering the O2 injection), a
OSTC (using fixed setpoint) and my good old Gekko on every dive.
OffTopic: Would be nice to enrich the Gekko profile manually with CC
mode, setpoint and gas actually used (set to air all the time in my case
as there is no Trimix support but having time and depth might be helpful
in case all my other electronics is failing). Might also be an issue
when merging dives from different computers and recognizing different
gas settings, different OC/CC mode, different deco...

Back to the Predator and downloading dive data: This unit reports some
more interesting stuff which I'd like to see in subsurface as well. So
Jef, this most likely addresses you in the first place:
- GF Settings (would be really nice to know, have not seen this in the
OSTC logs so far!?)
- Battery voltages (nice to have)
- CNS % (quite nice, recorded by Computer??)
- Firmware (nice to have)

Check this profile for what the Shearwater software is reporting:
http://trac.hohndel.org/attachment/ticket/5/tg.png
This also shows the not constant pO2. What would be interessting is what
the reports when one changes the GF settings while diving which is
possible for the Predator and with newest OSTC firmwares. If there is a
need, I would offer to do some test dives for this :-).

HTH,
Jan


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