APU Start L:Var/Lua for FSUIPC7 on Fenix A321

[Jacques Balayla]

Hi,

I've recently purchased a stream controller (Soomfon) and it's working beautifully with the Fenix L:Var/Lua file in FSUIPC - I assign a keyboard key and it binds to that function - then use the box to call on that key combo and absolutely everything works perfectly (overhead panel buttons, FCU, Lights, etc) but the APU start button does not seem to work after following normal procedures - APU Master SW - APU start - APU bleed. The master switch works and so does the bleed - but not the APU start - any ideas why?

My Lua file is the following:

-- Toggle APU Start Button
local val = ipc.readLvar("S_OH_ELEC_APU_START")

if val == 0 then
    ipc.writeLvar("S_OH_ELEC_APU_START", 1)
else
    ipc.writeLvar("S_OH_ELEC_APU_START", 0)
end
 

[John Dowson]

Does the lvar change values? Ifthe script is sunning as expected and the lvar is changing values, then you need something more than just to set that lvar.
Why not try the presets instead: APU Start Button Push and APU Start Button Release

Use logging to see if the script is running and the lvar is being updated: set logging for Lua Plugins and WAPI debug level logging.

[Jacques Balayla]

Will try and report back. Do you have the APU Start Button Push and APU Start Button Release  l:var functions for the fenix?

[John Dowson]

  On 6/9/2025 at 5:43 PM, Jacques Balayla said:

Do you have the APU Start Button Push and APU Start Button Release  l:var functions for the fenix?

Expand  

They are MF presets, and there is also FNX320_APU_START_SWITCH.
You can assign to presets directly (check the select fir Preset checkbox), or in lua you can use ipc.execPreset function.

I don't have the fenix to check these.

John

 

[John Dowson]

Btw, the calc code for FNX320_APU_START_SWITCH is:
    (L:S_OH_ELEC_APU_START) 2 +  (>L:S_OH_ELEC_APU_START)

i.e. it is incrementing the lvar by 2, not 1. So maybe try:

- Toggle APU Start Button
local val = ipc.readLvar("S_OH_ELEC_APU_START")

if val == 0 then
    ipc.writeLvar("S_OH_ELEC_APU_START", 2)
else
    ipc.writeLvar("S_OH_ELEC_APU_START", 0)
end

The calc code for the press/release presets looks rather strange to me, as it seems to be sending two values to the lvar, which I didn't think possible:
    push: 1 (L:S_OH_ELEC_APU_START) ++ (>L:S_OH_ELEC_APU_START)
    release: 0 (L:S_OH_ELEC_APU_START) ++ (>L:S_OH_ELEC_APU_START)
    
If the presets are not working, you can ask about this on the MF support discord server (MSFS2020 channel).

John

[Jacques Balayla]

Hi John,

Tried your code - im afraid it doesn't work.

So odd that it's just the APU start - even with the right variables.

Im really at a loss here...

 

[John Dowson]

  On 6/10/2025 at 4:40 PM, Jacques Balayla said:

Tried your code - im afraid it doesn't work.

Expand  

Did you try the presets? As I said, if they are not working, you can ask about this on the MobiFligh support on Discord.

  On 6/10/2025 at 4:40 PM, Jacques Balayla said:

So odd that it's just the APU start - even with the right variables.

Im really at a loss here...

Expand  

How does that variable change when you start it manually? Do you also see any events or input events  when starting it manually?
It could be that something else is needed.

You can also try inspecting the switch behavior to see how it works - see https://www.badcasserole.com/uncovering-input-events-using-the-msfs2020-model-behavior-dialog/