From: Niels Kolthoff <nkolthoff@gmail.com>
To: Simon Thelen <urday@student.kit.edu>
Cc: linux-rt-users@vger.kernel.org
Subject: Re: Low USB polling frequency with RT-PREEMPT
Date: Tue, 5 Sep 2017 19:53:17 +0200 [thread overview]
Message-ID: <CAD2hpBUsMz70-502BhOzxnH8H6zka3N86CNBspXizKr4WH5aNQ@mail.gmail.com> (raw)
In-Reply-To: <20170905150539.GF2607@anonymous>
Hi Simon,
Not sure if this helps; are you polling the actuators using usb-serial io?
I've had performance issues reading from the raspberry pi serial port.
see: http://www.spinics.net/lists/linux-rt-users/msg16880.html
On Tue, Sep 5, 2017 at 5:05 PM, Simon Thelen <urday@student.kit.edu> wrote:
> Hello,
>
> We have some Dynamixel robitic actuators hooked up via USB to an Ubuntu
> 14.04 system running the 4.4.79-rt92 kernel. When using a kernel built
> without the realtime patches (CONFIG_PREEMPT not set) we can query the
> bus at 1000Hz (2 devices at 500Hz each) whereas with the realtime kernel
> (CONFIG_PREEMPT=y, CONFIG_PREEMPT_RT_FULL=y) we only get 62.5Hz per
> device. The USB device requests Ivl=0ms in both cases and the issue
> isn't related to load etc. The polling rate is always 62.5Hz (It takes
> ~15ms for every read()).
>
>
> Is this a known limitation of USB with the CONFIG_PREEMPT_RT patches and
> is there any method to improve the polling rate?
>
> --
> Simon Thelen
> --
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prev parent reply other threads:[~2017-09-05 17:53 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-05 15:05 Low USB polling frequency with RT-PREEMPT Simon Thelen
2017-09-05 17:53 ` Niels Kolthoff [this message]
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