From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail.kapsi.fi ([217.30.184.167]:46039 "EHLO mail.kapsi.fi" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753293Ab3KNOE3 (ORCPT ); Thu, 14 Nov 2013 09:04:29 -0500 Message-ID: <5284D863.1080306@iki.fi> Date: Thu, 14 Nov 2013 16:04:19 +0200 From: Antti Palosaari MIME-Version: 1.0 To: Hans Verkuil , Andy Walls , LMML Subject: SDR API libv4lconvert remove packet headers in-Kernel or userspace Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-media-owner@vger.kernel.org List-ID: Hello Should I feed whole raw USB packet to libv4lconvert or rip headers off inside Kernel and feed only data? It is very trivial to remove headers in kernel and in a case of USB it does not even cost about nothing as you have to mem copy data out from URB in any case (if you do it on that phase). Lets take a most complex case I have. There is not only raw data, but some meta-data to process samples. In that case those samples are bit-shifted according to control bits in order to increase nominal sample resolution from 10 to 12 bits (not sure if it is bit shift or some other algo, but shifting bits sounds reasonable and testing against RF-signal generator results looked correct as it is now implemented). So do I feed that whole USB packet to userspace or do I have to remove headers + do bit bit shifting and forward only raw samples to userspace? That example could be found from: drivers/staging/media/msi3101/sdr-msi3101.c Here is what on USB packet looks like: +=============================================================== | 00-1023 | USB packet type '384' +=============================================================== | 00- 03 | sequence number of first sample in that USB packet +--------------------------------------------------------------- | 04- 15 | garbage +--------------------------------------------------------------- | 16- 175 | samples +--------------------------------------------------------------- | 176- 179 | control bits for previous samples +--------------------------------------------------------------- | 180- 339 | samples +--------------------------------------------------------------- | 340- 343 | control bits for previous samples +--------------------------------------------------------------- | 344- 503 | samples +--------------------------------------------------------------- | 504- 507 | control bits for previous samples +--------------------------------------------------------------- | 508- 667 | samples +--------------------------------------------------------------- | 668- 671 | control bits for previous samples +--------------------------------------------------------------- | 672- 831 | samples +--------------------------------------------------------------- | 832- 835 | control bits for previous samples +--------------------------------------------------------------- | 836- 995 | samples +--------------------------------------------------------------- | 996- 999 | control bits for previous samples +--------------------------------------------------------------- | 1000-1023 | garbage +--------------------------------------------------------------- regards Antti -- http://palosaari.fi/