Thanks for the responses, and especially the sample code.
The problem I was having was solved, it appears, when I changed my  
reference to IOFireWireAVCLibAsynchronousCommand creation.

// BEFORE
IOFireWireAVCLibAsynchronousCommand **async_command ;
// LATER..
result = (*avcUnit)->createAVCAsynchronousCommand( avcUnit, command,  
cmdLen, myCallback, (void*) pRef, async_command);

// NOW
IOFireWireAVCLibAsynchronousCommand *async_command ;
// LATER..
result = (*avcUnit)->createAVCAsynchronousCommand( avcUnit, command,  
cmdLen, myCallback, (void*) pRef, &async_command);

Don't ask me why but the 2nd version, where I create a pointer using  
'&' in last arg (as is done in the sample code), worked.
Tommy





On Nov 12, 2005, at 4:25 PM, Eric Anderson wrote:

> Could it be as simple as: asynch_command is an uninitialized  
> variable, and you passed it to createAVCAsynchronousCommand where a  
> pointer was expected, so createAVCAsynchronousCommand crashes/hangs/
> fails when trying to dereference your pointer?
>
> Maybe Niels or Andy can answer the part about where to get the  
> response.
>
> Eric
>
>
>
> On Nov 11, 2005, at 3:23 PM, Tommy Schell wrote:
>
>
>> Hi,
>>
>> I'm using the a/vc asynchronous interface, having a little trouble.
>>
>>
>> With the following declarations:
>>
>> // FIRST, A CALLBACK
>> void myCallback( void *pRefCon,  
>> IOFireWireAVCLibAsynchronousCommand *pCommandObject) {
>>
>>         printf("From my async callback!!\n");
>> }
>>
>> // THEN, IN MAIN().....
>>
>> void *pRef;
>>     IOFireWireAVCLibAsynchronousCommand  **async_command;
>>                UInt8   command[20];
>>                 UInt32  cmdLen = 0;
>> .......
>>
>> .......    // GET INTERFACE, ETC
>>             // SET UP COMMAND BUFFER
>>
>>                // open the AVC unit interface
>>                 result = (*avcUnit)->open( avcUnit );
>>
>> // HERE, IT CHOKES
>>  result = (*avcUnit)->createAVCAsynchronousCommand( avcUnit,  
>> command, cmdLen, (IOFireWireAVCLibAsynchronousCommandCallback)  
>> &myCallback, pRef, async_command);
>>
>>                 if( kIOReturnSuccess == result )
>>                         result = (*avcUnit)-
>> >AVCAsynchronousCommandSubmit( avcUnit, *async_command);
>>
>>                 result = (*avcUnit)->AVCAsynchronousCommandRelease  
>> ( avcUnit, *async_command);
>>
>>
>>
>> If, after opening the avcUnit, I use the AVCCommand() call  
>> instead, everything's fine.
>> But when I try the async calls, it chokes on the 1st one.
>> The most likely candidates for trouble in the argument list of the  
>> createAVCAsynchronousCommand call, I suppose, are the 4th and 5th  
>> args.
>> Especially the 5th call:  do I need to be passing in something  
>> besides a null pointer as void* pRefCon?
>> I tried passing a pointer to a UInt32, but that didn't help.
>>
>> Also, how does one get access to the response of the command?  
>> There's nowhere to pass a response pointer, as there is in the  
>> AVCCommand() call.
>>
>> Thanks,
>> Tommy Schell
>>
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