Re: PCI driver in userspace

[Richard Gooch]

Pete Zaitcev writes:
> >> I think this is a good example to start with. It has all the
> >> interresting features. I hope it also has interrupt handling
> >> to userspace (by generating SIGIO's). 
> > 
> > It hasn't, it just continually polls the I/O ports for 
> > completition.
> > 
> >> Although I dont know if this is a good idea in the first place.
> > 
> > I think it depends on the interrupt frequency, and other things.
> > 
> > Stelian.
> 
> PCI interrupts must be deactivated in the device before an
> interrupt driver returns and unmasks interrupt in the CPU.
> User processes run with interrupts open. This is why purely
> user level interrupts are IMPOSSIBLE (regardless of interrupt
> frequency).
> 
> Two natural ways to work around this problem are:
> 
> 1. Run user processes with interrupts closed (or at least one
> interrupt source disabled, if your architecture allows that).
> This is what RTOSes often do. I do not think it can be easily
> done on generic Linux.
> 
> 2. Write a small driver that deactivates interrupts and queues
> interrupt events (with SIGIO and some other means). Personally,
> I think that it is dumb in most cases, because once you wrote
> that driver stub, it takes very little work to move the rest
> of the driver into the kernel. The notable exception is XFree86,
> of course.
> 
> We must ask someone to add this to FAQ on tux.org.

Send me a patch to the HTML file.

				Regards,

					Richard....
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