[linux-dvb] Re: Busy waiting in i2c_busy_rise_and_fall (was: Re: Re: full featuredcard without signal and required video memory investigation)

[John Dalgliesh <johnd@syd.microforte.com.au>]

On Mon, 14 Jul 2003, Oliver Endriss wrote:

> On Sunday 13 July 2003 20:21, Andreas Kool wrote:
> > I can confirm the faster firmware upload and faster tuning here with
> > my DVB-C rev1.3
> 
> Apparently the speedup of the I2C transfers is the main improvement of 
> the patch. Hopefully all devices can handle a 275 kHz clock rate.
> I don't know why the I2C bus clock was set to 10.3 kHz.

I don't actually know what I'm talking about (:-) but I remember reading
that ICs that are slower than the clock rate of the I2C bus can 'stretch
out' the read/write cycles and take as long as they want.

Here we go: Note 2 on page 123 of the SAA7146 manual.

> > But if i'm unplug the antenna cable (please remember: DVB-C), the
> > kdvb-fe-0:0 process jumps to 43,1% CPU-load like always :-(
> 
> Meanwhile I did a bit more testing and found that the cpu load caused by 
> the frontend process varies. I was not able to reproduce the good 
> results of my first test but the load is still below 14% (before 
> 30-35%). Strange.
> 
> > But new: If i re-attach the antenna cable, the actually tuned
> > programme reapears after no visible delay - great!
> 
> Is this really caused by the patch? If yes, I don't know why. ;-)
> 
> Oliver

{P^/

btw I seem to have got into bits of code that I should only have entered 
if I read the status as being not busy twice in succession after an I2C 
transfer... but there were a lot of other things I was doing wrong then so 
this is probably irrelevant.



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