pvrxxx, linux code and modules

John-Mark Gurney gurney_j at resnet.uoregon.edu
Tue Apr 17 00:18:21 UTC 2007

usleepless at gmail.com wrote this message on Tue, Apr 17, 2007 at 00:51 +0200:
> On 4/16/07, John-Mark Gurney <gurney_j at resnet.uoregon.edu> wrote:
> >Greg 'groggy' Lehey wrote this message on Mon, Apr 16, 2007 at 15:20 +0930:
> >> - I need to understand better how tuners work.  I've been thinking of
> >>   writing a document on the subject, something that people could use
> >>   for help when writing drivers.  If you know of anything, even
> >>   partial or badly laid out, please let me know.
> >
> >Just to reiterate, tuner code really should be located in userland..
> >it's not time sensitive, and can't corrupted state of the kernel..
> >
> >As for tuners, most/all of them communicate through the i2c bus...
> >The tuner is programed w/ the frequency to tune, and depending upon
> >the range of frequence will turn on/off various transistors to change
> >some of the analog curcuit behavior...
> >
> >My HDTV device drive does all the tuning from userland...
> which driver is this?

The DViCO FusionHDTV 5 Lite driver:

I have two tuners working in my system at home.

> >It was
> >a lot easier to get it working using userland than having to constantly
> >load/unload kernel modules, and risk crashing the machine...
> you are absolutely spot on about this. it's that i did build upon
> pvr250 which had the tuner in kernel space, so i didn't think about
> it. otherwise i might have been influenced by the linux source, and i
> would have implemented in kernel space as well :-)
> but considering V4L(2), which has to support ioctl's changing the
> frequency, how could this work from userland?

Kill the V4L(2) API? :)  I have thought about doing a cdev bridge to
userland..  Effectively FUSE, but for cdev's instead of file systems...
This would put most/all the logic in userland, and w/ some mmapping
magic, can have similar/same performance for high speed devices like

  John-Mark Gurney				Voice: +1 415 225 5579

     "All that I will do, has been done, All that I have, has not."

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