[Xenomai] Write a hard real time usb driver

[Xenomai] Write a hard real time usb driver

[Seda Seda]

Hello everyone,

I try to write a hard real time usb driver. I communicate my device  using
open(), read() etc. My device is a gpio module.I am coding a kernel module
to communicate the device using xenomai on real time. But I am not sure
that this way is reasonable. If I should going on this way, what should I
implement? Could you give me some example or link to write hard real time
usb driver for* physical* device? I wrote a driver for virtual device, it
was ok.

Re: [Xenomai] Write a hard real time usb driver

[Jeroen Van den Keybus]

> I try to write a hard real time usb driver. I communicate my device  using
> open(), read() etc. My device is a gpio module.


I assume you want to control an USB host controller using a GPIO interface ?


> I am coding a kernel module
> to communicate the device using xenomai on real time. But I am not sure
> that this way is reasonable. If I should going on this way, what should I
> implement? Could you give me some example or link to write hard real time
> usb driver for* physical* device?


I cannot help you with that, but one important issue to consider is that
the USB protocol itself operates with small, hardware controlled time slots
of 1 ms (USB1.x) or 125 usec (USB2.0). You may therefore need a significant
amount of software to properly distribute real-time traffic in these -
essentially asynchronous - slots. The latency of a real-time process
waiting for USB data can therefore also be as large as the time slot
duration. If your real-time requirements are modest, you may be able to
live with that. Still, count on a major software effort: just have a look
at the Linux USB driver framework.

Alternatively, you could check if you can synchronize your real-time
process with the USB controller frame rate.


Jeroen.

Re: [Xenomai] Write a hard real time usb driver

[Jan Kiszka]

On 2014-11-03 09:03, Jeroen Van den Keybus wrote:
>> I try to write a hard real time usb driver. I communicate my device  using
>> open(), read() etc. My device is a gpio module.
> 
> 
> I assume you want to control an USB host controller using a GPIO interface ?
> 
> 
>> I am coding a kernel module
>> to communicate the device using xenomai on real time. But I am not sure
>> that this way is reasonable. If I should going on this way, what should I
>> implement? Could you give me some example or link to write hard real time
>> usb driver for* physical* device?
> 
> 
> I cannot help you with that, but one important issue to consider is that
> the USB protocol itself operates with small, hardware controlled time slots
> of 1 ms (USB1.x) or 125 usec (USB2.0). You may therefore need a significant
> amount of software to properly distribute real-time traffic in these -
> essentially asynchronous - slots. The latency of a real-time process
> waiting for USB data can therefore also be as large as the time slot
> duration. If your real-time requirements are modest, you may be able to
> live with that. Still, count on a major software effort: just have a look
> at the Linux USB driver framework.
> 
> Alternatively, you could check if you can synchronize your real-time
> process with the USB controller frame rate.
> 

FWIW, we still don't have USB 2.0 support (though I vaguely remember
previous efforts in that direction), but at least a framework for 1.1
devices with Xenomai 2.6.x. It is in successful use for industrial
sensors. Code is available here:

http://git.kiszka.org/?p=usb4rt.git;a=summary

As the targeted sensors generate data streams only with 1 ms period, the
1.1 limitation was not an issue so far.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux

Re: [Xenomai] Write a hard real time usb driver

[Gilles Chanteperdrix]

On Mon, Nov 03, 2014 at 06:12:11PM +0100, Jan Kiszka wrote:
> On 2014-11-03 09:03, Jeroen Van den Keybus wrote:
> >> I try to write a hard real time usb driver. I communicate my device  using
> >> open(), read() etc. My device is a gpio module.
> > 
> > 
> > I assume you want to control an USB host controller using a GPIO interface ?
> > 
> > 
> >> I am coding a kernel module
> >> to communicate the device using xenomai on real time. But I am not sure
> >> that this way is reasonable. If I should going on this way, what should I
> >> implement? Could you give me some example or link to write hard real time
> >> usb driver for* physical* device?
> > 
> > 
> > I cannot help you with that, but one important issue to consider is that
> > the USB protocol itself operates with small, hardware controlled time slots
> > of 1 ms (USB1.x) or 125 usec (USB2.0). You may therefore need a significant
> > amount of software to properly distribute real-time traffic in these -
> > essentially asynchronous - slots. The latency of a real-time process
> > waiting for USB data can therefore also be as large as the time slot
> > duration. If your real-time requirements are modest, you may be able to
> > live with that. Still, count on a major software effort: just have a look
> > at the Linux USB driver framework.
> > 
> > Alternatively, you could check if you can synchronize your real-time
> > process with the USB controller frame rate.
> > 
> 
> FWIW, we still don't have USB 2.0 support (though I vaguely remember
> previous efforts in that direction),

There is one here:
http://sourceforge.net/projects/usb20rt.berlios/

Have not looked at the code though.

-- 
					    Gilles.

Re: [Xenomai] Write a hard real time usb driver

[Jan Kiszka]

On 2014-11-03 18:14, Gilles Chanteperdrix wrote:
> On Mon, Nov 03, 2014 at 06:12:11PM +0100, Jan Kiszka wrote:
>> On 2014-11-03 09:03, Jeroen Van den Keybus wrote:
>>>> I try to write a hard real time usb driver. I communicate my device  using
>>>> open(), read() etc. My device is a gpio module.
>>>
>>>
>>> I assume you want to control an USB host controller using a GPIO interface ?
>>>
>>>
>>>> I am coding a kernel module
>>>> to communicate the device using xenomai on real time. But I am not sure
>>>> that this way is reasonable. If I should going on this way, what should I
>>>> implement? Could you give me some example or link to write hard real time
>>>> usb driver for* physical* device?
>>>
>>>
>>> I cannot help you with that, but one important issue to consider is that
>>> the USB protocol itself operates with small, hardware controlled time slots
>>> of 1 ms (USB1.x) or 125 usec (USB2.0). You may therefore need a significant
>>> amount of software to properly distribute real-time traffic in these -
>>> essentially asynchronous - slots. The latency of a real-time process
>>> waiting for USB data can therefore also be as large as the time slot
>>> duration. If your real-time requirements are modest, you may be able to
>>> live with that. Still, count on a major software effort: just have a look
>>> at the Linux USB driver framework.
>>>
>>> Alternatively, you could check if you can synchronize your real-time
>>> process with the USB controller frame rate.
>>>
>>
>> FWIW, we still don't have USB 2.0 support (though I vaguely remember
>> previous efforts in that direction),
> 
> There is one here:
> http://sourceforge.net/projects/usb20rt.berlios/
> 
> Have not looked at the code though.

Yeah, that's the one I recalled. Seems dead, unfortunately.

Jan

-- 
Siemens AG, Corporate Technology, CT RTC ITP SES-DE
Corporate Competence Center Embedded Linux

Re: [Xenomai] Write a hard real time usb driver

[Hasret Sarıyer]

Thanks your help.

2014-11-03 19:22 GMT+02:00 Jan Kiszka <jan.kiszka@siemens.com>:

> On 2014-11-03 18:14, Gilles Chanteperdrix wrote:
> > On Mon, Nov 03, 2014 at 06:12:11PM +0100, Jan Kiszka wrote:
> >> On 2014-11-03 09:03, Jeroen Van den Keybus wrote:
> >>>> I try to write a hard real time usb driver. I communicate my device
> using
> >>>> open(), read() etc. My device is a gpio module.
> >>>
> >>>
> >>> I assume you want to control an USB host controller using a GPIO
> interface ?
> >>>
> >>>
> >>>> I am coding a kernel module
> >>>> to communicate the device using xenomai on real time. But I am not
> sure
> >>>> that this way is reasonable. If I should going on this way, what
> should I
> >>>> implement? Could you give me some example or link to write hard real
> time
> >>>> usb driver for* physical* device?
> >>>
> >>>
> >>> I cannot help you with that, but one important issue to consider is
> that
> >>> the USB protocol itself operates with small, hardware controlled time
> slots
> >>> of 1 ms (USB1.x) or 125 usec (USB2.0). You may therefore need a
> significant
> >>> amount of software to properly distribute real-time traffic in these -
> >>> essentially asynchronous - slots. The latency of a real-time process
> >>> waiting for USB data can therefore also be as large as the time slot
> >>> duration. If your real-time requirements are modest, you may be able to
> >>> live with that. Still, count on a major software effort: just have a
> look
> >>> at the Linux USB driver framework.
> >>>
> >>> Alternatively, you could check if you can synchronize your real-time
> >>> process with the USB controller frame rate.
> >>>
> >>
> >> FWIW, we still don't have USB 2.0 support (though I vaguely remember
> >> previous efforts in that direction),
> >
> > There is one here:
> > http://sourceforge.net/projects/usb20rt.berlios/
> >
> > Have not looked at the code though.
>
> Yeah, that's the one I recalled. Seems dead, unfortunately.
>
> Jan
>
> --
> Siemens AG, Corporate Technology, CT RTC ITP SES-DE
> Corporate Competence Center Embedded Linux
>
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