From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from smtp-vbr14.xs4all.nl ([194.109.24.34]:1799 "EHLO smtp-vbr14.xs4all.nl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752567Ab3LMOGY (ORCPT ); Fri, 13 Dec 2013 09:06:24 -0500 Message-ID: <52AB1447.9090601@xs4all.nl> Date: Fri, 13 Dec 2013 15:05:59 +0100 From: Hans Verkuil MIME-Version: 1.0 To: Antti Palosaari CC: linux-media@vger.kernel.org, Mauro Carvalho Chehab Subject: Re: [PATCH RFC 4/4] v4l: 1 Hz resolution flag for tuners References: <1386806043-5331-1-git-send-email-crope@iki.fi> <1386806043-5331-5-git-send-email-crope@iki.fi> <52A96C00.8060607@xs4all.nl> <52A9F0C7.2050602@iki.fi> In-Reply-To: <52A9F0C7.2050602@iki.fi> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: On 12/12/2013 06:22 PM, Antti Palosaari wrote: > Hi Hans! > > On 12.12.2013 09:55, Hans Verkuil wrote: >> On 12/12/2013 12:54 AM, Antti Palosaari wrote: >>> Add V4L2_TUNER_CAP_1HZ for 1 Hz resolution. >>> >>> Signed-off-by: Antti Palosaari >>> --- >>> include/uapi/linux/videodev2.h | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/include/uapi/linux/videodev2.h b/include/uapi/linux/videodev2.h >>> index 6c6a601..1bac6c4 100644 >>> --- a/include/uapi/linux/videodev2.h >>> +++ b/include/uapi/linux/videodev2.h >>> @@ -1349,6 +1349,7 @@ struct v4l2_modulator { >>> #define V4L2_TUNER_CAP_RDS_CONTROLS 0x0200 >>> #define V4L2_TUNER_CAP_FREQ_BANDS 0x0400 >>> #define V4L2_TUNER_CAP_HWSEEK_PROG_LIM 0x0800 >>> +#define V4L2_TUNER_CAP_1HZ 0x1000 >>> >>> /* Flags for the 'rxsubchans' field */ >>> #define V4L2_TUNER_SUB_MONO 0x0001 >>> >> >> I was wondering, do the band modulation systems (V4L2_BAND_MODULATION_VSB etc.) cover SDR? > > There is no such modulations defined for SDR hardware level. SDR > demodulation is done by software called DSP (digital signal processing) > in host computer. > > In ideal case, SDR receiver has only 1 property: ADC (analog to digital > converter) sampling rate. So in that case the band modulation would be 0, right? > > But as digital signal processing is very CPU intensive when sampling > rates are increased, there is very often RF tuner used to down-convert > actual radio frequency to low-IF / BB. Then ADC is used to sample that > baseband / low-IF signal and only small sampling rate is needed => > stream is smaller => DSP does not need so much CPU. How does the application know that there is an RF tuner? I assume that the app needs to know this? As you can probably tell, I basically know nothing about SDR, so forgive me if I am asking stupid questions. I just want to make sure all bases are covered when it comes to the V4L2 API. Regards, Hans >> Anyway, I'm happy with this patch series. As far as I am concerned, the next step would >> be to add documention and I would also recommend updating v4l2-compliance. Writing docs >> and adding compliance tests has proven useful in the past to discover ambiguous API specs. > > I will do these at finally when I drivers and applications are tested to > be working. > > regards > Antti >