[linux-dvb] Re: [patch] TT C-1200 USB wrong frequency

Thomas Kaiser linux-dvb at kaiser-linux.li
Wed May 2 08:30:09 CEST 2007


Trent Piepho wrote:
> On Wed, 2 May 2007, Petri Helin wrote:
>>>>>>> If your device is using the philips tda1316 tuner, i think there is a
>>>>>>> problem in setting the correct Band. 162 MHz and above should be band
>>>>>>> 2 (Mid-Band). But in dvbc_philips_tdm1316l_tuner_set_params band 1 is
>>>>>>> set for frequencies below 200 MHz:
>>>>>>>     // determine charge pump
>>>>>>>     tuner_frequency = params->frequency;
>>>>>>>     if      (tuner_frequency <  87000000) {return -EINVAL;}
>>>>>>>     else if (tuner_frequency < 130000000) {cp = 3; band = 1;}
>>>>>>>     else if (tuner_frequency < 160000000) {cp = 5; band = 1;}
>>>>>>>     else if (tuner_frequency < 200000000) {cp = 6; band = 1;} <<==
>>>> Just to let you all know, in case you didn't see an earlier post about
>>>> tuning problems with TechnoTrend's C1500 card, the above change broke
>>>> tuning on those cards with frequencies under 160MHz.
>>> That doesn't seem possible, that it would break tuning for under 160Mhz.
>>>
>>> This change only affects the band for frequencies between 160 Mhz and 200
>>> Mhz, nothing outside this of this range should be affected in any way.
>>>
>>> What frequency does it break exactly?
>>>
>> The problem seams to be that the fix was applied in the wrong file -
>> budget-ci.c instead of dvb-ttusb-budget.c as supposed to.
>> dvbc_philips_tdm1316l_tuner_set_params in budget-ci.c uses an offset of
>> 36125000 for frequency before assigning the charge pump and band (what's
>> the need for this offset??) and therefore the failing frequencies (for
>> example 138MHz and 146MHz) are actually interpreted as something between
>> 160MHz and 200MHz when the band is set.
> 
> This offset is the IF frequency.  Search this list for "if frequency" and
> you should find plenty of information.
> 
> These tuning functions are old code, and should be converted into users of
> dvb-pll.  I'll put it on my dvb-pll todo list, right after fmd1216me is
> committed.
> 
> In budget-ci.c, philips_tdm1316l_tuner_set_params() uses 159 Mhz
> *pre-IF-offset* as the low-mid band switch point.  While
> dvbc_philips_tdm1316l_tuner_set_params() uses 200 MHz *post-IF-offset* as
> the band switch point.
> 
> In dvb-ttusb-budget.c, philips_tdm1316l_tuner_set_params() uses 159 MHz
> pre-IF-offset.  And dvbc_philips_tdm1316l_tuner_set_params() uses 200 MHz
> pre-IF-offset.
> 
> This 4x duplication of the same code with random bugs in some copies is
> exactly why this should be converted to dvb-pll!
> 
> I think it is highly likely that the band switch point post-IF-offset is
> the same for both the DVB-T and the DVB-C tuners.
> 
> driver		tuner	post-IF-offset low-mid band switch point
> budget-ci	DVB-T	195 1/8 MHz (to two decimal places)
> budget-ci	DVB-C	200 MHz     (this is the likely correct value)
> ttusb-budget	DVB-T	195 1/8 MHz (to two decimal places)
> ttusb-budget	DVB-C	236 1/8 MHz (this is clearly wrong)
> 
> My guess is the correct value is 200 MHz, not 195 1/8th.  It would only
> make a difference for a channel between 159 MHz and 163.87 MHz.  Does
> anyone have the datasheet to check?

Hello Trent, Andrew

Anyway, this 
http://linuxtv.org/hg/v4l-dvb?cmd=changeset;node=e7c424bbf9aa;style=gitweb 
change is wrong anyway and should be reverted.

I don't know what is the correct way to fix the ttusb-buget DVB-C tuner 
issue. But it looks reasonable to share the same code (without bugs) for 
all 4 devices.

Thomas





-- 
http://www.kaiser-linux.li



More information about the linux-dvb mailing list