Re: [Xenomai-help] Non-Real-Time Asynchronous Notification

[Jan Kiszka <jan.kiszka@domain.hid>]

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Robert McCullough wrote:
> Hi Jan,
> 
>   --> -----Original Message-----
>   --> From: jan.kiszka@domain.hid [mailto:jan.kiszka@domain.hid]
>   --> Sent: Friday, March 21, 2008 4:10 PM
>   --> To: rob@domain.hid
>   --> Cc: xenomai@xenomai.org
>   --> Subject: Re: [Xenomai-help] Non-Real-Time Asynchronous Notification
>   --> 
>   --> Robert McCullough wrote:
>   --> > Hi Jan,
>   --> >
>   --> >   --> -----Original Message-----
>   --> >   --> From: jan.kiszka@domain.hid [mailto:jan.kiszka@domain.hid]
>   --> >   --> Sent: Thursday, March 20, 2008 3:29 PM
>   --> >   --> To: rob@domain.hid
>   --> >   --> Cc: xenomai@xenomai.org
>   --> >   --> Subject: Re: [Xenomai-help] Non-Real-Time Asynchronous
>   --> Notification
>   --> >   -->
>   --> >   --> Robert McCullough wrote:
>   --> >   --> > Hi,
>   --> >   --> >
>   --> >   --> > How do I signal an asynchronous notification from a RTDM
>   --> real-time
>   --> >   --> task to a
>   --> >   --> > non-real-time user-space Linux thread?
>   --> >   --> > Do I use Non-Real-Time Signaling Services
>   --> (rtdm_nrtsig_init,..)?
>   --> >   --> > If so, how?
>   --> >   --> >
>   --> >   --> > Here is the current code that I am trying to port to RTDM.
>   --> >   --> >
>   --> >   --> > Current driver code to signal non-real-time Linux thread:
>   --> >   --> >
>   --> >   --> > 	// If event
>   --> >   --> > 	if(event){
>   --> >   --> > 		// and signal asynchronous readers
>   --> >   --> > 		if (kmdpr_device->async_queue)
>   --> >   --> >
> kill_fasync(&kmdpr_device->async_queue,
>   --> > SIGIO,
>   --> >   --> > POLL_IN);
>   --> >   --> > 	}
>   --> >   -->
>   --> >   --> Just push this code in the rtdm_nrtsig handler and trigger the
>   --> handler
>   --> >   --> execution from RT context.
>   --> >   -->
>   --> >   --> Jan
>   --> >
>   --> > [Robert McCullough]
>   --> > Ok, I understand that but how do I specify the file operation fasync
>   --> in my
>   --> > rtdm_device?  How do I replace or update the code marked TODO?
>   --> 
>   --> In fact, there is no fasync support available with RTDM, specifically
>   --> as
>   --> using signals under real-time constraints is a bad idea (not only
>   --> because Xenomai has no hard-RT signal support).
>   --> 
>   --> But before suggesting any alternative pattern: What does your
>   --> application actually require to work? How does asynchronous
>   --> driver/application interaction currently look like?
>   --> 
>   --> Jan
> 
> [Robert McCullough]
> Here is a little background on how my driver works.
> The driver is the interface/control for an AC servo drive which controls an
> AC motor.  The interface to the drive is done through a dual-ported RAM.
> The I/O from the servo drive is updated and an IRQ is triggered from the
> servo drive through the DP RAM to our MPC5200 at a 4 kHz rate.  In my IRQ
> handler I read, process, and update the I/O in the RAM.  Some of the data
> from the servo drive contains status bits that represent asynchronous
> events/faults from the drive that needs to be passed up to the user
> application.  In my current non-real-time driver I used fasync to send a
> SIGIO signal to the user application whenever one of these events/faults
> changed and then the application would read the status bits with an ioctl
> call and process them.
> 
> I hope this clarifies the requirements a little.
> How would you suggest I solve this in my RTDM driver?

Well, a classic pattern is to encapsulate the async event handling in 
one or more dedicated threads that block-wait on those events. Check the 
RTDM profile for serial devices for such a channel. This has the 
advantage that you can cleanly specify the handling priority, 
specifically compared to "normal" operations.

HTH,
Jan


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