Re: [Xenomai-help] How to avoid a tight real time loop

[Alexis Berlemont <alexis.berlemont@domain.hid>]

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
> 
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-- 
Alexis.