> The latencies are almost certainly caused by the USB host controller
> driver. I'm planning improvements to uhci-hcd which should
> help reduce
> the latency, but it will still be on the large side. And I
> won't have
> time to write the changes to the driver for several months.
Any numbers about the expected "large side"?
We would need <30 microseconds irq latency,
and <<1 milliseconds rt application latency.
> The best solution is to stop using uhci-hcd. Get a PCI card
> with an OHCI
> or EHCI (high-speed) controller. They do much more work in hardware,
> reducing the amount of time the driver needs to spend with interrupts
> disabled.
The hardware is invariable. It is an embedded system with no PCI slots.
And it seems to be possible with UHCI,
because vxWorks allows USB stick transfers in operation without
missing latency requirements.
I do not require rt on the USB, it may block its own irq as long as
it likes, but it should not affect other irqs.
--
Klaus Kusche
Entwicklung Software - Steuerung
Software Development - Control
KEBA AG
A-4041 Linz
Gewerbepark Urfahr
Tel +43 / 732 / 7090-3120
Fax +43 / 732 / 7090-8919
E-Mail: [email protected]
www.keba.com
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