From mboxrd@z Thu Jan  1 00:00:00 1970
Date: Wed, 16 Jun 2010 00:11:16 +0200
From: Alexis Berlemont <alexis.berlemont@domain.hid>
Message-ID: <20100615221116.GB3087@domain.hid>
References: <4C177276.7060005@domain.hid>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <4C177276.7060005@domain.hid>
Subject: Re: [Xenomai-help] How to avoid a tight real time loop
List-Id: Help regarding installation and common use of Xenomai
	<xenomai.xenomai.org>
List-Unsubscribe: <https://mail.gna.org/listinfo/xenomai-help>,
	<mailto:xenomai-help-request@domain.hid>
List-Archive: </public/xenomai-help>
List-Post: <mailto:xenomai@xenomai.org>
List-Help: <mailto:xenomai-help-request@domain.hid>
List-Subscribe: <https://mail.gna.org/listinfo/xenomai-help>,
	<mailto:xenomai-help-request@domain.hid>
To: Daniele Nicolodi <daniele@domain.hid>
Cc: xenomai@xenomai.org

Hi,

Daniele Nicolodi wrote:
> Hello. In my application I need to read data from an ADC card in blocks
> of a given number of samples. For efficiency I'm using an mmapped buffer
> to exchange data with the ADC driver. I'm setting up the acquisition,
> and then calling a loop like this:
> 
> unsigned int required = <compute required number of bytes>;
> unsigned int read = 0;
> while (1) {
>   while (read < required) {
>     read = a4l_pool(...);
>   }
>   process(buffer, ...);
> }
> 
> However if I run this loop in a real time thread the tight while loop is
> an obvious cpu hog: the watchdog kicks in and kills the thread.
> 
> There is not an analogy API that can be used to require a certain amount
> of data to the ADC driver. How can I code this loop to let other
> processes to run?

As a matter of fact, there is something in the API which could have
helped you in an unmapped configuration. If you set the flag
A4L_CMD_BULK in the field "flags" of the command structure, a call to
a4l_async_read() only returns when the data size specified as argument
is available. 

Unfortunately, I have not done the same thing with a4l_poll, I might
have added the requested size as an additional argument to a4l_poll. 

Any idea on how to extend the API without breaking it ?

> 
> Thanks. Cheers,
> -- 
> Daniele
> 
> _______________________________________________
> Xenomai-help mailing list
> Xenomai-help@domain.hid
> https://mail.gna.org/listinfo/xenomai-help

-- 
Alexis.