Re: iPad Class 1 Audio---Corrections
Re: iPad Class 1 Audio---Corrections
- Subject: Re: iPad Class 1 Audio---Corrections
- From: Dominik Peklo <email@hidden>
- Date: Tue, 4 May 2010 00:45:28 +0800
That's kind of disappointing :( It should really refuse to enumerate async sink straight away if it can't handle it.
Ever since I heard about iPad supporting USB Audio as a host, I was expecting a port of Mac OS X's existing, fully capable and proven driver. I wonder why it's not being used - after all iPhone OS should be pretty much the same as Mac OS at the Darwin & CoreAudio level? Guess there's much less commonality then I suspected.
Any plans to develop this further into a fully functional USB Audio Class driver as in Mac OS?
Regards,
Dominik
On May 3, 2010, at 22:30 , Gordon Rankin wrote:
> Gang,
>
> Spoke a little early.... Put the Total Phase Beagle USB 480 Analyzer on the link.
>
> 1) Even though the iPad + Camera USB Connection kit selects the Asynchronous DAC and plays out of it... it does fail to send the feedback pipe any in's (0x83) which means there is no feedback associated with the link and in some cases this will cause over or underruns sometime down the pike. In my case it must be because I do some stuff internally to pre-buffer the interface and therefore I did not hear anything.
>> Endpoint 0x01 - Isochronous Output Address: 0x01 (OUT)
>> Attributes: 0x05 (Isochronous asynchronous data endpoint)
>> Max Packet Size: 192
>> Polling Interval: 1 ms
>> Class-Specific AS Audio EndPoint - Control output Attributes: 0x00 bLockDelayUnits: 0x00 (UNDEFINED)
>> wLockDelay: 0 Endpoint 0x83 - Isochronous Input Address: 0x83 (IN)
>> Attributes: 0x01 (Isochronous no synchronization data endpoint)
>> Max Packet Size: 3
>> Polling Interval: 1 ms
>
> 2) The suspend sequence does work but it is a little weird... When the iPad is turned off, it sends like 10 seconds of standard zero packets (i.e. 44.1 nine 176 + one 180) for silence and then set's the interface to OFF waits for the ACK then delays 10 more seconds and does a Host Disconnect.
>
> 3) Standard HID stuff like volume, mute etc... seem to work fine.
>
> 4) Multichannel... I plugged the Creative Labs xFi/xMod into the iPad which does 5.1 virtual stuff at 44.1/16. The iPad did select it and it did send the correct amount of data (i.e. nine 528 byte and one 540 byte) per 1ms frame. But the data was not sequenced right and it sounded like the chipmunks. This is also an async unit and it did verify #1 and the iPad did not send in's (0x81) to the xMod.
>
>> Endpoint 0x01 - Isochronous Output Address: 0x01 (OUT)
>> Attributes: 0x05 (Isochronous asynchronous data endpoint)
>> Max Packet Size: 540
>> Polling Interval: 1 ms
>> Class-Specific AS Audio EndPoint - Control output Attributes: 0x00 bLockDelayUnits: 0x00 (UNDEFINED)
>> wLockDelay: 0 Endpoint 0x81 - Isochronous Input Address: 0x81 (IN)
>> Attributes: 0x01 (Isochronous no synchronization data endpoint)
>> Max Packet Size: 3
>> Polling Interval: 1 ms
> 5) First attempt at multiple interfaces (i.e. 16 bit and 24 bit) did not work. I will have to try a couple more things as I did still offer up 44.1, 48, 88.2 and 96 which we know are not all supported. But basically it loops in a reset, get Descriptor, Set Interface then loop. Audio comes out of internal speakers.
>
> 6) I had an old iMic from Griffin here and plugged that in. It has stereo Adaptive output and mono microphone. Both iPod and Videos output at 16/44.1. I did not see any activity on the in port for the Microphone. But I have seen elsewhere were someone tested a USB headset ok. So I imagine that depends on if an application opens the microphone input on the iPad.
>
> More soon, but it looks like presently only Adaptive is really supported.
>
> Thanks
> Gordon
>
> --
> J. Gordon Rankin
> Owner and Chief Scientist
> ====== Wavelength Audio, ltd ======
>
> --
> J. Gordon Rankin
> Owner and Chief Scientist
> ====== Wavelength Audio, ltd ======
> High-End Audio since 1981
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> http://www.WavelengthAudio.com
> ===================================
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> ===================================
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