On Fri, Mar 09, 2001 at 09:05:44AM -0500, [EMAIL PROTECTED] wrote:
> I once discovered that the standard UART drivers will only deliver data
> to user level processes on "kernel ticks". Since you are running a
> 100Hz scheduler, that would limit the native UARTS to 10ms minimum
> latency and it looks like you got 10ms very consistently.
>
> I don't know where this limitation is so I don't know of the USB serial
> ports are subject to it but it looks like maybe the Edgeport isn't but
> the keyspan is. ...is the Edgeport driver you used based on the
> "standard USB serial support"? I think I recently saw a patch to
> change it so it would be but recall that it previously stood alone.
Yes, this was my recently posted Edgeport driver that worked with the
"standard USB serial support".
> I suspect that you would get different results if you patched the
> kernel for 1024Hz scheduling. ...would you mind doing that experiment?
> Also, try 115,200 bps if you can?
Sure, I'll try to do that this weekend, and also dig up some other
devices I have around here.
> > Hope this helps,
>
> Yup. At leat the Edgeport data suggests that the latency I am seeing
> isn't inherent to USB. I'm still wondering if it is somehow tunable
> though.
I think the only way you will be able to tune it is by buying a
different device :)
greg k-h
--
greg@(kroah|wirex).com
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