[linux-dvb] Re: Driver problems

[Holger Waechtler <holger@convergence.de>]

Torbjörn Jansson wrote:
>  
> > > Do you have one of the cards where the PWM value stored in 
> > the card's 
> > > EEPROM needs to be overridden? I don't remember exactly for 
> > > which cards 
> > > this was required or improved things, maybe you want to check 
> > > the mail 
> > > archives or just try to override it using the 'pwm=' module 
> > parameter 
> > > for ves1820.o and optimize this value by trial'n'error...
> > >
> > > Please check the mail archives for the background info.
> > >
> > > Holger
> > In the syslog I get a line like: "DVB: VES1820(0): pwm=0x40"
> > I'll have to try changing it.
> >
> > If this works, maybe a few lines in some readme file coud be 
> > added to the
> > dvb drivers so that others that run into the same problem 
> > atleast know what
> > to try.
> >
> > What does this pwm thing do?
The VES1820 has a 'Pulse-Width-Modulated Output' which can be programmed 
to output a constant PWM signal via i2c. Usually such signals are then 
low-pass filtered to an adjustable DC and used to control local board 
voltages.

On the Technotrend DVB-C boards this signal is used to adjust one of the 
parameters that vary with fabrication tolerance (don't remember how it 
was connected exactly, investigate your DVB-C board or check the mailing 
list archives to be sure). If the EEPROM does not contains the correct 
value the card won't work fine.

The Windows software even contains a calibration utility to adjust this 
parameter that gets started at installation time, but it does not seems 
to store the new value in the EEPROM but somewhere on the hard disk for 
the windows driver only.

Then there was a second problem - some time ago people reported that 
some of the cards needed other values than the ones stored in the 
EEPROM. Since we did not found a easy automagic solution that worked for 
all cards and it's even possible that the optimal required PWM value 
changes with the card's age the discussion came up to either reprogram 
the EEPROM or to override the EEPROM parameter with an optional module 
parameter. But again - these are only my fuzzy memories - please check 
the archives to get the 'real' background and to follow the discussion.

Holger



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