Re: Some major problems of em28xx chip base TV devices in linux

Re: Some major problems of em28xx chip base TV devices in linux

[Mauro Carvalho Chehab]

Em 27-04-2011 11:06, a b escreveu:
> Hello all
> 
>   Before anythings, i beg pardon of whom the matter of this e-mail is not related to; please excuse me.
> ------------------------------------------------------------------
>   Unfortunately i could not until now, use any DVB hardware on any version of linux; i tested many of them but none of them can be correctly used. :-(
>   I tired from testing and testing all things about combination of my linuxes and DVBs.
>   Please help me with all things that you know, and please do not tell the repeated things that i already tested, and please only think about the exact problem.

Please, don't mix Kernel driver issues with userspace ones. Different groups of
developers (and different mailing lists) are used for each userspace tool.
I won't comment about userspace DVB tools, as I don't maintain them.

>   i myself is familiar with unix and linux from about 19 years ago, and have done many low level programming on linux and unix in kernel and user spaces, till now. Thus please don't explain the inexact things and some non important things like options of /etc/syslog.conf or hardware testing of computer main memory!!
>   Please focuse your mind, only on the problems, thanks.

As you're a developer, the better way to improve is to make patches fixing the 
issues you noticed and submit them to the mailing lists. You're the only one
capable of reproducing your environment, in terms of channels, board configuration,
etc, as almost all work done here are made by volunteer people.

>   I tested this DVB-Stick with 2 linux versions, Debian and Ubuntu. Debian was lenny-i686 with kernel: 2.6.35.10 (that this kernel was compiled by myself from is complete source downloaded from www.kernel.org <http://www.kernel.org> with complete activation of all device drivers as kernel module) and Ubuntu was 10.10-amd64 (with 2 versions of kernel: 2.6.35.22 and 2.6.38.8, both of them was installed from the main ubuntu repository "archive.ubuntu.com <http://archive.ubuntu.com>" )
>   Both of linuxes were running on one computer, with a brief hardware of 2.8-GHz Intel Core2due E7400 CPU & 1 Giga-Ram & 2 Sata Hard disk & PK5PL Asus motherboard & Nvidia-G9500-GT graphic card.

If you think you have a driver issue, just use the latest development tree, available
at linuxtv.org. It contains the latest version of the drivers. the media-build.git is
the best way to get it. If you want to submit patches, you should get also the media-tree.git,
and generate patches against it.

>   i will explain my testings after this brief writing about my main (big) 7 problems:
>     1- The only software that could show me some of TV programs, was kaffeine, and no other softwares ( included mythtv & VLC & mplayer & w_scan & scan of dvb-utils ) could show any things.

Clearly, an userspace issue.

>     2- No any software could find any digital (DVB) channels during the scanning ( including even kaffeine).

Had you try w_scan and dvb-apps (from linuxtv.org)? What happens with dvb-apps with -v enabled?

>     3- Some of violations from standard encoding of DVB packets is done in my 25 digital channels, but experienced programmers of Win-Xp softwares find them and make some work around for them and thus we (linux programmers) must do the same things.

If the transmissions in your Country is violating the standard DVB, you'll need to fix the source
code of the applications. This may explain the problems you're having. No one else at the community 
can do anything to help you on it, because they don't have access to the same streamings as you have.

Mauro.

Re: Some major problems of em28xx chip base TV devices in linux

[Mauro Carvalho Chehab]

Em 27-04-2011 18:29, a b escreveu:
> 

> Hello Mauro and thanks But,
> 
> because of my testings, i guess most of problems are in the kernel space not the user space, and my asking for your help was because of that matter. and i though that those log files and information files attached to my previous e-mail, can help you as a developer of some parts of related kernel drivers, to finding the problems is a short time, to solve them.
> 
>     Please don't think about correcting the problems by myself, because it is obvious that any one that worked on em28xx driver, can find and fix the problems, for more than 10 times faster than me, because i have not worked on this driver at all. And also if i want to do so, i first must learn two considerable matter: a- the DVB structure and its packets' protocols ( that is not little thing), b- the manner of the em28xx and xc2038 chips ( that is not little thing too).  :-(
> 
> i am waiting for your help, and i can do some tests that you need, but if you notice exactly to my hardware and linuxes (explained in before e-mail) , you see that you can prepare the same test bed for you, easily.


Let me explain how things work:

The tuner (xc3028) just tunes into some frequency.

The demod basically decodes the DVB carriers and provide some stats showing
that DVB carriers were properly locked/decoded. Some demods also provide DVB Program ID
filtering.

For DVB, all that em28xx does is to serve as a bridge between the PCI bus, the DVB
streams and the board internal bus to control the demod/tuner.

A working DVB driver (tuner+demod+bridge) will just provide a MPEG-TS stream to the userspace
application, and let it do the DVB processing.

The userspace application is responsible to open the MPEG-TS packets and extract the required info
from it (service provider, Program ID's, program name, video stream, audio stream), and to decode 
the video and audio streams according to MPEG2 Video/MPEG2 audio (or whatever video/audio standard
is used by your TV broadcasters).

So, basically, the userspace app should implement the hardest part, based on the ETSI and MPEG 
standards.

According to what you've said, with Kaffeine, you're able to watch to channels. That means 
that tuner, demod and bridge are working. You also said that you tested other boards and noticed
the same trouble. So, it doesn't look like a driver issue. The DVB drivers are well tested in
Europe, where ETSI is fully used. There aren't many DVB developers outside Europe, so locale 
adjustments is sometimes needed. For example, I needed to adjust some things at the DVB applications
I care, in order to fix some decoding stuff on DVB-C and DVB-S due to some differences on the way
the spec is used in Brazil, and to be able to use some LNBf types found here.

You also said that the DVB operators you're listening don't fully follow the ETSI and/or MPEG specs.
As such, the userspace application needs to have some extra logic to understand the differences
between the standards and what the broadcasters are doing. This is probably standardized (at least
for DVB-T) on some docs from your Country's TV Boureau.

That's why only someone with access to such specs and capable of receiving the signals available
there will be capable of adding the extra decoding stuff into the existing applications.

Ah, with respect to the high CPU used on it, this is due to software MPEG-2 decoding. Some applications
like VLC will use your GPU to decode MPEG2, decreasing a lot the amount of load on the CPU, depending
on the video board and X11 driver that you're using. An special configuration is geneally needed, in
order to enable vdpau and similar technologies.

Mauro.


PS.: Please don't remove the C/C to the linux-media ML, as others may have similar issues, or may
have already worked on some solution/workaround.