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Re: Re: USB Isochronous Pipe

Hi Jonathan, Maruyama,

if you are programming for a usb 2.0 device then your trouble is that you are mixing up usb frames and usb microframes. In usb 2.0 frames are transfered to the device in microframes. Every usb frame contains 8 microframes.

err = (*intf)->ReadIsochPipeAsync(intf,ISO_PIPEREF,isoRequests [i].buffer,nextFrame,ISO_REQFRAMES,isoRequests[i].frames, isoCallback, &isoRequests[i]);

ReadIsocPipe takes usb micro frames as the numFrames argument; so what you are telling the system in this code is to transfer 1 ( !! ) usb frame!! That is too little and will fail. In my driver i usually transfer 128 usb frames ( that would be 128 * 8 microframes ). To make it even more confusing the currentFrame argument is in usb frames ( not microframes ). So your line

nextFrame+=ISO_REQFRAMES;

is also wrong for usb 2.0 because nextFrame should be in usb frames. nextFrame+=ISO_REQFRAMES/8 would be correct.

ReadIsochPipeAsync also has problems when you set the frStatus field wrong, ( especially in USB 1.1 ), even though i've seen bug fixes out there that claim that this problem was fixed. Try setting it to kUSBLowLatencyIsochTransferKey before sending the frames on the bus.

And one more idea: ReadIsochPipeAsync also returns an error if all frames have failed. On my device the first hundred frames just tend to fail so i just ignore the errors until i see that the stream is running. For instance, the usb controller will set the frStatus field to a non zero value if it noticed that not all bytes that were requested were really transferred ( and this happens quite often ). To make it more complicated: sometimes the error code of frStatus is a mac os x error code and sometimes it's the usb error code ( even though, again, apple claims to have fixed this problem, they apparently didn't ( not sure if this still occurs in the newest mac os x version ) ).

Please tell exactly which error code you are receiving.

Hope that helped

Greetings from Germany

Fabian

P.S: Oh yeah. As a general advice: update to the newest mac os x version. Some older versions really had problems with iso transactions.
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