Re: [Xenomai-help] RTDM driver hints

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

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juanba romance wrote:
> Hello all, i am re-writing a old linux driver which i did myself some
> time ago, cause i am in charge to provide a RT system framework. This
> is one of the first steps so i have followed the RTDM model to do the
> stuff.
> Now i also have enough time to change its ugly capabilities/defects
> but i am a little stuck right now..
> 
> I would like to improve my previous design fully buffering the
> incoming user data flow on write method so a input FIFO it's planned.
> The FIFO will be emptied using a rt-task created from the "open"
> procedure and signalled from the "write" method before the user flow
> exit. The point is:
> where the FIFO handler references should be defined ?
> 
> I have take a look to the serial driver 16550 and my code is really
> biased by its data device definition strategy ( obviously this is my
> first RTDM monster ;-) and i need some guide ), instead of my
> proposal, its design empty the TX FIFO from the IRQ service stuff
> where the user context was passed as argument at the "open" call, so
> all the parts are softly linked..
> 
> I would prefer to add the above program capability to avoid rewrite as
> much as possible the current ISR symbol.
> but i don't know the beast strategy to be applied to overcome the .
> 
> I have pass the "context" field dev_private area pointer to the
> rt_task "by hand" but its value is really weird. Should this kind of
> information be defined globally trough the "static" stuff and pass
> this argument to the rt_task_init symbol

Before going into details on how to pass references between driver tasks
etc.:

Why do you want to establish a dedicated task for transmission? Is the
job you have to perform there too heavy for IRQ context? Keep in mind
that such a task requires additional management (assign reasonable
priorities e.g.) and adds further latencies. It's no magic bullet, but
it may be appropriate if there is actually a lot of work to do that
shall not block other, more important jobs.

Jan


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