> On 2 May 2019, at 18:06, Hans Petter Selasky <[email protected]> wrote:
> On 2019-05-02 10:22, O'Connor, Daniel wrote:
>>> On 2 May 2019, at 06:15, Hans Petter Selasky <[email protected]> wrote:
>>> On 2019-05-01 10:34, O'Connor, Daniel wrote:
>>>> I don't have a solid hypothesis for the failures as yes but one thing I'd
>>>> like to make sure is that the USB stack is keeping the USB hardware busy
>>>> with pending requests - does anyone know if the USB FIFO code does that
>>>> automatically?
>>>
>>> Only the XHCI driver supports HW based double buffering of BULK transfers.
>> Ahh interesting - is that a ECHI hardware limitation or a driver one?
>
> It is an EHCI hardware "limitation". It is possible to queue up more jobs
> with the EHCI, but it ends that you get a race with the hardware you'll need
> to catch. I think it is related to how receiving short packets are handled.
OK, thanks.
To be honest I would much prefer to work out why this particular hardware &
software seem to drop the ball for such a long time - 50msec without the kernel
getting to schedule something (on a basically idle system) is quite perplexing
to me.
>>> I suppose you are using BULK. Else you will need to use ISOCHRONOUS
>>> transfers.
>> Yes it's using bulk transfers.
>> I did consider isochronous transfers when I started this project but I
>> wasn't sure if there would be enough bandwidth (but perhaps I read the spec
>> wrong). I imagine there would be enough for this data rate but we have
>> others at higher speeds (eg 35MB/sec).
>
> If you want reliable data transfer, BULK is the best.
OK, yes, has to be reliable :)
>> Related to bandwidth - are there any statistics gathered about how busy a
>> port is?
>
> No, but I wanted to add a text-graph frontent to usbdump to collect this info
> realtime. Else use a USB wire-analyzer.
I wondered about this too, probably easier than instrumenting the EHCI driver I
suppose.
Sadly I don't have a USB analyser and even if I did the system in question is
in another country :(
--
Daniel O'Connor
"The nice thing about standards is that there
are so many of them to choose from."
-- Andrew Tanenbaum
_______________________________________________
[email protected] mailing list
https://lists.freebsd.org/mailman/listinfo/freebsd-usb
To unsubscribe, send any mail to "[email protected]"
