What sort of devices would use Iso transfers with Packets larger than 512 bytes

[tkafafi]

In the system I'm using, the host cannot support Isochronous transfers with packet sizes larger than 512 bytes.
So I'm trying to get an idea how limiting is this restriction in real life.

1) What sort of devices use Iso with large packets?  Webcam are the first that come to mind, any others ?
2) If a device is used which requests large iso , is there a way for the host driver to inform a device driver that it doesn't support  this configuration?
3) for the case of a webcam, does this result in the webcam crashing, failing gracefully or operating at a lower setting ? I.e Would the webcam not enumerate at all or would the class driver configure the webcam to use lower bandwidth (e.g lower reolution or lower frame rate or lower pixel size settings) so it will still work in a lower setting ?
4) What packet size range do webcams typically use ?

Thanks
Tamer
 

[Barry Twycross]

Is this high speed or full speed?

Webcams are the obvious answer. You might find high end audio devices (with lots of channels, high sample rates, and high bit depth could get there).

There is really no way for the host to tell a driver about a constraint like this, its just plain broken. What the host could do is lie about the amount of bandwidth available and fail requests with a large packet size for lack of bandwidth. The device might back off to a lower bandwidth alt. If it can back off, you'll get a degradation in quality, frame rate frame size etc. If it can't back off, it'll totally fail to initialise.

I'd expect to find web cams wanting the maximum, 3x1024 byte packets. We ship lots of cameras like that.

[tkafafi]

Thanks Barry. your reply was very helpfull and informative.