From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pz0-f171.google.com ([209.85.222.171]:54627 "EHLO mail-pz0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751257AbZJXQbz (ORCPT ); Sat, 24 Oct 2009 12:31:55 -0400 Received: by pzk1 with SMTP id 1so291184pzk.33 for ; Sat, 24 Oct 2009 09:32:00 -0700 (PDT) Message-ID: <4AE32BFD.1090000@gmail.com> Date: Sun, 25 Oct 2009 00:31:57 +0800 From: "David T. L. Wong" MIME-Version: 1.0 To: v4l-dvb Subject: Re: Details about DVB frontend API References: <20091022211330.6e84c6e7@hyperion.delvare> In-Reply-To: <20091022211330.6e84c6e7@hyperion.delvare> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: Jean Delvare wrote: > Hi folks, > > I am looking for details regarding the DVB frontend API. I've read > linux-dvb-api-1.0.0.pdf, it roughly explains what the FE_READ_BER, > FE_READ_SNR, FE_READ_SIGNAL_STRENGTH and FE_READ_UNCORRECTED_BLOCKS > commands return, however it does not give any information about how the > returned values should be interpreted (or, seen from the other end, how > the frontend kernel drivers should encode these values.) If there > documentation available that would explain this? > > For example, the signal strength. All I know so far is that this is a > 16-bit value. But then what? Do greater values represent stronger > signal or weaker signal? Are 0x0000 and 0xffff special values? Is the > returned value meaningful even when FE_HAS_SIGNAL is 0? When > FE_HAS_LOCK is 0? Is the scale linear, or do some values have > well-defined meanings, or is it arbitrary and each driver can have its > own scale? What are the typical use cases by user-space application for > this value? > > That's the kind of details I'd like to know, not only for the signal > strength, but also for the SNR, BER and UB. Without this information, > it seems a little difficult to have consistent frontend drivers. > > Thanks, Hi all, I am a bit late in this discussion. I just want to raise out a problem of the current architecture of FE + tuner. Indeed, the actual "Signal Strength" can only be get from tuner. Tuner has amplifier internally and AGC. So demod can never know the accurate signal strength. Demod only roughly knows signal-to-noise ratio. Correct me if I am wrong that I found FE == Demod in current code. Thus, asking FE to report the signal strength is not appropriate. To achieve reporting actual signal strength, in commercial proprietary code, it is a combination of readings from tuner + demod. Which in turn, should sit in card/dongle specific code. Regards, David T.L. Wong