Re: [9fans] "gpio device" for Plan 9

[Krystian Lewandowski <krystian.lew@gmail.com>]

Wiadomość napisana przez erik quanstrom <quanstro@quanstro.net> w dniu 31 gru 2013, o godz. 20:50:

> On Tue Dec 31 14:40:29 EST 2013, edgecomberts@gmail.com wrote:
> 
>> Erik,
>> 
>> Just for the purposes of edification (and curiosity), are you able to
>> elaborate on "long reads"? Its understandable such a scheme would be
>> implemented in the network drivers, but how exactly does it work, as
>> opposed to a polling scheme or an ISR? I will, of course, Google in a sec
>> as well.
> 
> it could be that i misunderstood the op's point.  what i understood from the
> original post was a scheme was envisioned where a user process would poll a
> status file to get interrupt status.  if i understood this correctly, then providing
> an interrupt file that returns even 0 bytes when there's an interrupt would be
> an alternative providing interrupt semantics to the up.  there are some 
> bits to work out if the user process falls behind, but it's no different than a
> network device.
> 
> does that answer your question?
> 
> - erik
> 

I’ll answer at the bottom, to not make even more mess i did before. :)

I’m not even sure what is my point of view. For ISR i was thinking about an interrupt routine writing something (a single byte) to a file when an interrupt occurs - writing using functions defined in qio - something similar to /dev/kprint - reading user process is waiting for new data if i understood the behavior correctly. It is not clear to me how this „0 bytes” method:
> providing
> an interrupt file that returns even 0 bytes when there's an interrupt would be
> an alternative providing interrupt semantics to the up
could be implemented and how ioproc is related (how ioread can be woken up with 0 bytes returned). But now, my mind isn’t quite clear now.

As i said i don’t know much about BCM, Plan 9 and the whole thing and basic GPIO implementation seemed to be a good entry point. Now i’m trying to figure out how it can be extended in the future, regarding your feedback. But if you think it is worth to extend this thread with new information then that would be great.

Thanks for this discussion!
Krystian