B4J Question RPi & B4j - How to delay BT.initialise

[Mark Read]

I am connecting a headless RPi 2 with bluetooth dongle to a tablet running a B4A App. Everything was working fine some months ago but suddenly I have a problem.

The b4j app is a non UI and can be started from the menu to debug etc. It is also started in the rc.local on boot.

If I boot the Rpi, it seems that the BT is not ready for about 5 seconds after the GUI appears (the icon is grey and then goes blue). During this time, my app has tried to initialise BT, fails and closes. If I start the app manually via the menu, it works fine as the icon is blue - clear I hope.
This is the code I am using(b4j ver. 4.70):

'Start bluetooth
    bt.Initialize("bt")
    If bt.IsEnabled = False Then
        Log("Bluetooth not available1")
        ExitApplication
    End If
   
    RPiStatus.State=True    ' turn on green LED to show ready status of RPi
   
    Log($"My address: ${GetBluetoothAddress}"$)
    Log("***************************************************************************")
    bt.Listen        'bt_Connected is called when connection is made
   
    StartMessageLoop

I think it would be better to use a

Wait For bt.IsEnabled = True

instead of the If-End. Am I correct or not and would this be the correct code?

Many thanks.

 

[Knoppi]

You can insert in rc.local a sleep 5s command before your b4j prg is called

 

[Mark Read]

Thx Knoppi, already tried 20 secs - didn't work.

 

[Knoppi]

Try

raspi-config

boot-options/wait-for-network

Edit:
Not ideal but it works in most cases
insert in crontab
sudo crontab -e
@reboot sleep 5 && /full/path/to/your/app

 

[Mark Read]

That only applies to the network or not. I need bluetooth.

 

[Erel]

This is the code I am using(b4j ver. 4.70):

You should use the latest version of B4J.

You can do something like:

Do While bt.IsEnabled = False
Sleep(1000)
Loop

Or better:

Dim start As Long = DateTime.Now
Do While bt.IsEnabled = False
If DateTime.Now > start + 30000 Then
  Log("BT not available.")
  ExitApplication
End If
Sleep(1000)
Loop

Note that this code can't be in AppStart sub. It should be in a different sub that you call from AppStart.

 

[OliverA]

It should be in a different sub that you call from AppStart

Why?

 

[Erel]

It is only relevant for non-ui programs.

Sub AppStart (Args() As String)
 Sleep(100)
 StartMessageLoop
End Sub

Sleep and Wait For are equivalent to Return. This means that AppStart will return before StartMessageLoop is called and the program will terminate before the sub will be resumed.

 

[OliverA]

It is only relevant for non-ui programs.

Whew... I already thought this (not to use in AppStart) may apply to UI apps too. Panic averted...

 

[Erel]

In UI projects (and B4A and B4i projects) the message loop is created for you before AppStart is called.

The only other relevant case is standard server handles: https://www.b4x.com/android/forum/t...t-for-sleep-in-server-handlers.81833/#content