Krog Kronos Intro Videos

Timing in iOS

See this link: http://atastypixel.com/blog/experiments-with-precise-timing-in-ios/

The bottom line is that no form of NSTimer/RunLoop/etc. is going to provide sufficiently accurate timing for anything musical....

Misery (Continued)

So I move the project over to the iPhone.

Everything works perfectly - no problems with NSLog() or breakpoints flaking out...

What the hell!

Misery (Continued)

So I found this link.  A way to reset the debugger to some degree:

1. Close XCode

2. Delete the $project/build/*

3. Delete /Developer/Platforms/iPhoneOS.platform/DeviceSupport/4.2.1

4. Restart XCode

5. Go to organizer and agree to let it download "collect" what it wants (symbols) from the device

6. In Organizer, again right click -> Add device to provisioning portal


Doing this I now have a project which ignores breakpoints and/or NSLog statements about 10% or so of the time - which is almost tolerable.  I set a breakpoint at the start of the project - if it doesn't stop I just restart it.


Its really hard to imagine what these folders have to do with NSLog and breakpoints...

Misery (Continued)

So the best I can do to fix the NSLog() and breakpoint problem on this particular project (or a project using the same file, i.e., another independently constructed duplicate project) is to diddle the Code Signing settings for "Any iOS" between "iPhone Developer" and "iPhone Developer: me XXXXXX".

Good news on the audio front...

It turns out that when you instantiate an AudioUnit the settings of "[ AVAudioSession sharedInstance] setCategory:" matter. 

For example, with the category set to "AVAudioSessionCategoryPlayback" you can instantiate an AudioUnit with input but the render loop will not be called.  Changing the category to "AVAudioSessionCategoryPlayAndRecord" after instantiation does not change this - even if you stop and restart the AudioUnit. 

So if you don't use the Record category your render loop will simply not be called.

I have been looking around at various documentation for AudioUnits wonder what you are allowed to do and not do with multiple AudioUnits simultaneously.  Certainly it seems you should be able to have more than one at any given time and in fact as long as they don't overlap on input and output and you have the right category set on instantiation this seems to be true from my experiments.

But there is little documentation of this - at least I could not find it.

AudioUnits and AVAudioPlayer do not work well together either.  However, I probably did not have the categories set properly so this might be part of the cause though some other testing leads me to believe there are other incompatibilities.

Basically I eliminated AVAudioPlayer as well as some other MixerHostAudio code I was using.  I now do my own mixing and sound triggering in a pair of AudioUnits and it seems far simpler and more efficient.

Misery (Continued)

So I have still not been able to figure out completely what's going on with the NSLog() and breakpoints.

I tried Googling this 'xcode gdb "sharedlibrary apply-load-rules all" ' where I did find this post (here) on various "code signing" issues.

It seems like the gdb debugger does not always attach to the remote iOS process unless some voodoo in the "code signing" section of the "Build" configuration is set to the proper phase of the moon.

Diddling this seems to make NSLog() and breakpoints work again:

I changed the 'Any OS' tag to some default.

This Apple software is totally flaky and unreliable in this regard.

[ UPDATE ]  While this worked a few times in a row on XCode 3 no dice in XCode 4.

Diddling the same parameter does not cause NSLog() or breakpoints to work.

[ UPDATE ] I regenerated the provisioning profiles and upgraded a different iPad to 4.3.5 (I was on 4.3.3 for the problems above).  After reinstalling all of this it seems to be working ("seems to be working" basically means I have several time connected and disconnect the iPad over an hour or so and each time breakpoints continue to work.

Now that I think about it I probably updated iTunes to 10.4.1 (10) - but I cannot recall if the problems started before that or not - I think not in this case.

Is it fixed?

The jury is still out...

XCode, AudioUnits, Breakpoints and NSLog Misery...

So I am debugging an iOS AudioUnit render callback function.

I have the exact same code working in a standalone project so I know that everything is correct.  The code in question looks something like this:

OSStatus recordingCallback(void *inRefCon,
                 AudioUnitRenderActionFlags * ioActionFlags,
                 const AudioTimeStamp *inTimeStamp,
                 UInt32 inBusNumber,
                 UInt32 inNumberFrames,
                  AudioBufferList *ioData)
{   
  AudioBuffer buffer;
  AudioBufferList bufferList;
      ...
 
   buffer.mNumberChannels = 1;
  buffer.mDataByteSize = inNumberFrames * 2;
  buffer.mData = malloc( inNumberFrames * 2 );
  bufferList.mNumberBuffers = 1;
  bufferList.mBuffers[0] = buffer;

  ...

  status = AudioUnitRender(audioUnit,
                           ioActionFlags,
                           inTimeStamp,
                           inBusNumber,
                           inNumberFrames,
                           &bufferList);

  if (status != noErr)
  {
    NSLog(@"An AudioUnitRender error occurred (%d).", status);
  }
  ...
}
 
The buffer arrangement is such that only a single buffer is being used.

In the stand alone project status is always equal to noErr and the NSLog function is never called and the render works fine.

When I copy this code without change into the main project suddenly all hell breaks loose.

First off, status starts reliably returning -50 (which indicates a bad parameter is being passed to AudioUnitRender).  

Bad parameter? 

How on earth can that be as the exact same parameters work perfectly in the standalone project.  After endless diddling to ensure that I am not doing something stupid I start to look for other reasons this might be failing.

Eventually I discover a post on some Apple developer list where someone else has a similar problem.  They trace this to the use of AVAudioPlayer and its associated start method.  (Basically this means if you have some other part of the project playing background music the above code ceases to work correctly and indicates bad parameters are being passed.)

Commenting out this code (the AVAudioPlayer code along with some MixerHostAudio-derived code) appears to make the project work but I notice that I am no longer seeing NSLog output (the project barfs out all kinds of status as it boots up).  Then breakpoints seem to no longer work so I cannot tell if removing the use of AVAudioPlayer is really working or not.

Now I become extremely frustrated. 

How can NSLog simply cease to work?

So I think - well, this must be an XCode 4 problem...

I open the project in the latest version of XCode 3 and NSLog does not work there either nor do breakpoints...!!!

What the hell?  I curse Apple, Jobs, and the iOS development staff.

(This is made worse by recently discovering that Adobe CS 2 will not work on Lion, Lion being required to have the newest XCode 4 and no doubt iOS 5.  I want a law passed that requires Apple to compensate me for taking away functionality with required software releases...)

Now what?

More hours of Googling and diddling until if find this on StackOverflow (with some changes):

    1. Quit XCode 3/4.
    2. Open a terminal window and cd to the project directory
    3. cd into the .xcodeproj directory
    4. Delete everything except the .pbxproj file.

Or, in Finder Right/Option-Clicking on the .xcodeproj bundle, pick "Show Package Contents," and remove all but the .pbxproj file.

This seems to work - at least some of the time and sort of magically the breakpoints and NSLog output reappear and work as expected!

But then it flakes out again - sometimes working - sometime not.

I guess at this point the only things I can come up with are either

A) Somehow the render function is messing things up.  Everything works save for the microphone callback just fine - or at least it did - no flakies until I added in that extra AudioUnit code.  It seems as if this addition permanently wacked out XCode4 for this project (others at least appear to still work correctly including the standalone version of the AudioUnit.

B) Mixing to much AudioUnit stuff is a problem or flakey...  Others report the AVAudioPlayer problem with AudioUnit and other things (like playing movies).

More to come...