Re: About zero-length packet design for EHCI

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Thanks Alan,

that was very helpful.

/Bernd

Alan Stern wrote:
On Tue, 14 Jul 2015, Bernd Porr wrote:

I've got a question regarding ISO transfer. If the firmware is not providing data is the ISO urb returning zero packet length and if yes how can I check that in the driver? I'm working on a solution for my USBDUX driver where the ADC for example takes 800us to measure all data so that a couple of zero length packets were generated until new data has been created.

I assume you're talking about isoc-IN transfers where the device either
sends a 0-length packet or doesn't send any packet at all.  When that
happens, the corresponding urb_iso_packet_descriptor structure will
contain 0 for .actual_length and either 0 for .status (if a 0-length
packet was received) or -EXDEV for .status (if no packet was received). Your driver can check these values in the URB's completion routine.

Alan Stern


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