Re: XCHI bulk transaction latency, data lost, NAK stats

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Thanks, Alan, your answers are really helpful.
one more question:
> It depends on what other devices are attached to the USB bus.  They may
> or may not require some reserved bandwidth.
Is there any tool/method I can dump reserved or allocated bandwidth
info of each  USB device?

Thanks
Yunhua

On Sat, Aug 22, 2020 at 1:41 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Sat, Aug 22, 2020 at 01:35:28PM -0700, yunhua li wrote:
> > HI Alan Thanks for your response.
> > > What is the communication speed of the camera?  480 Mb/s (USB-2), 5000
> > Mb/s (USB-3) or something else?  And how much data does the camera send
> > for each frame?
> > It is 5000Mb/s (USB 3.0),  each video frame is about 2880000, 30 fps.
>
> So at 500 MB/s, and with less than 5 MB/frame, the expected transfer
> time for each frame is under 10 ms.  30 frames per second should be
> fine.
>
> > > 20 - 200 seconds?  That's an awfully long latency.  Much longer than you
> > would expect from random fuctuations; it indicates that something is
> > going badly wrong.
> > Sorry it is 0.02 ~ 0.2 seconds delay,  when image got corrupted,
>
> Okay, that's more like what one might expect.
>
> > > It depends on what other devices are attached to the USB bus.  They may
> > or may not require some reserved bandwidth.
> > There is no other USB device connected to the system.
> > if no other USB device, and no  Isochronous transaction, Bulk
> > transaction (This camera) should be able to use all bandwidth, am I
> > correct?
>
> Yes, that's right.
>
> Alan Stern



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