One (not-so-elegant) way to detect a signal is to look for the presence
of color in the signal. It is much quicker than querying a tuner. I have seen
this technique used to zip through the analog VHF TV broadcasts, then
enumerate the ones where a 'color' signal was picked-up. It reliably found
all known local stations -- even those with weak signals.
I don't currently have the code for doing this with the Bt878.
-- Peter
xyzzy@speakea
sy.org To: video4linux-list@xxxxxxxxxx@Internet
cc: (bcc: Peter Lohmann/Americas/NSC)
04/10/02 Subject: Re: Re: No signal detection
10:48 AM
On 10 Apr 2002, Gerd Knorr wrote:
> Alan McIvor wrote:
> > Hi,
> >
> > At the hardware level, the bt878 has a register which says whether or
> > not there is a video signal on the input (bit BT848_DSTATUS_PRES in
> > the dstat register), but I don't think this is available in user
> > space.
>
> video_tuner->signal = (BT848_DSTATUS & BT848_DSTATUS_HLOC) ? 0xFFFF : 0;
Not very useful. You can't query the tuner unless you have it selected as the
input. So if your card doesn't have a tuner, or you are using the composite
or s-video input, this won't work.
Most tuners have AFC bits that tell you if your frequency is too high or too
low, which you can't access via the driver either.
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