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HOWTO: Get An Avermedia DVB-T working under Linux |
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______________________________________________ |
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Table of Contents
Assumptions and Introduction
The Avermedia DVB-T
Getting the card going
Receiving DVB-T in Australia
Known Limitations
Further Update
Assumptions and Introduction
It is assumed that the reader understands the basic structure
of the Linux Kernel DVB drivers and the general principles of
Digital TV.
One significant difference between Digital TV and Analogue TV
that the unwary (like myself) should consider is that,
although the component structure of budget DVB-T cards are
substantially similar to Analogue TV cards, they function in
substantially different ways.
The purpose of an Analogue TV is to receive and display an
Analogue Television signal. An Analogue TV signal (otherwise
known as composite video) is an analogue encoding of a
sequence of image frames (25 per second) rasterised using an
interlacing technique. Interlacing takes two fields to
represent one frame. Computers today are at their best when
dealing with digital signals, not analogue signals and a
composite video signal is about as far removed from a digital
data stream as you can get. Therefore, an Analogue TV card for
a PC has the following purpose:
* Tune the receiver to receive a broadcast signal
* demodulate the broadcast signal
* demultiplex the analogue video signal and analogue audio
signal (note some countries employ a digital audio signal
embedded within the modulated composite analogue signal -
NICAM.)
* digitize the analogue video signal and make the resulting
datastream available to the data bus.
The digital datastream from an Analogue TV card is generated
by circuitry on the card and is often presented uncompressed.
For a PAL TV signal encoded at a resolution of 768x576 24-bit
color pixels over 25 frames per second - a fair amount of data
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is generated and must be processed by the PC before it can be |
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displayed on the video monitor screen. Some Analogue TV cards |
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for PCs have onboard MPEG2 encoders which permit the raw |
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digital data stream to be presented to the PC in an encoded
and compressed form - similar to the form that is used in
Digital TV.
The purpose of a simple budget digital TV card (DVB-T,C or S)
is to simply:
* Tune the received to receive a broadcast signal.
* Extract the encoded digital datastream from the broadcast
signal.
* Make the encoded digital datastream (MPEG2) available to
the data bus.
The significant difference between the two is that the tuner
on the analogue TV card spits out an Analogue signal, whereas
the tuner on the digital TV card spits out a compressed
encoded digital datastream. As the signal is already
digitised, it is trivial to pass this datastream to the PC
databus with minimal additional processing and then extract
the digital video and audio datastreams passing them to the
appropriate software or hardware for decoding and viewing.
_________________________________________________________
The Avermedia DVB-T
The Avermedia DVB-T is a budget PCI DVB card. It has 3 inputs:
* RF Tuner Input
* Composite Video Input (RCA Jack)
* SVIDEO Input (Mini-DIN)
The RF Tuner Input is the input to the tuner module of the
card. The Tuner is otherwise known as the "Frontend" . The
Frontend of the Avermedia DVB-T is a Microtune 7202D. A timely
post to the linux-dvb mailing list ascertained that the
Microtune 7202D is supported by the sp887x driver which is
found in the dvb-hw CVS module.
The DVB-T card is based around the BT878 chip which is a very
common multimedia bridge and often found on Analogue TV cards.
There is no on-board MPEG2 decoder, which means that all MPEG2
decoding must be done in software, or if you have one, on an
MPEG2 hardware decoding card or chipset.
_________________________________________________________
Getting the card going
In order to fire up the card, it is necessary to load a number
of modules from the DVB driver set. Prior to this it will have
been necessary to download these drivers from the linuxtv CVS
server and compile them successfully.
Depending on the card's feature set, the Device Driver API for
DVB under Linux will expose some of the following device files
in the /dev tree:
* /dev/dvb/adapter0/audio0
* /dev/dvb/adapter0/ca0
* /dev/dvb/adapter0/demux0
* /dev/dvb/adapter0/dvr0
* /dev/dvb/adapter0/frontend0
* /dev/dvb/adapter0/net0
* /dev/dvb/adapter0/osd0
* /dev/dvb/adapter0/video0
The primary device nodes that we are interested in (at this
stage) for the Avermedia DVB-T are:
* /dev/dvb/adapter0/dvr0
* /dev/dvb/adapter0/frontend0
The dvr0 device node is used to read the MPEG2 Data Stream and
the frontend0 node is used to tune the frontend tuner module.
At this stage, it has not been able to ascertain the
functionality of the remaining device nodes in respect of the
Avermedia DVBT. However, full functionality in respect of
tuning, receiving and supplying the MPEG2 data stream is
possible with the currently available versions of the driver.
It may be possible that additional functionality is available
from the card (i.e. viewing the additional analogue inputs
that the card presents), but this has not been tested yet. If
I get around to this, I'll update the document with whatever I
find.
To power up the card, load the following modules in the
following order:
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* modprobe bttv (normally loaded automatically)
* modprobe dvb-bt8xx (or place dvb-bt8xx in /etc/modules)
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Insertion of these modules into the running kernel will
activate the appropriate DVB device nodes. It is then possible
to start accessing the card with utilities such as scan, tzap,
dvbstream etc.
The frontend module sp887x.o, requires an external firmware.
Please use the command "get_dvb_firmware sp887x" to download
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it. Then copy it to /usr/lib/hotplug/firmware or /lib/firmware/
(depending on configuration of firmware hotplug).
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Receiving DVB-T in Australia
I have no experience of DVB-T in other countries other than
Australia, so I will attempt to explain how it works here in
Melbourne and how this affects the configuration of the DVB-T
card.
The Digital Broadcasting Australia website has a Reception
locatortool which provides information on transponder channels
and frequencies. My local transmitter happens to be Mount
Dandenong.
The frequencies broadcast by Mount Dandenong are:
Table 1. Transponder Frequencies Mount Dandenong, Vic, Aus.
Broadcaster Channel Frequency
ABC VHF 12 226.5 MHz
TEN VHF 11 219.5 MHz
NINE VHF 8 191.625 MHz
SEVEN VHF 6 177.5 MHz
SBS UHF 29 536.5 MHz
The Scan utility has a set of compiled-in defaults for various
countries and regions, but if they do not suit, or if you have
a pre-compiled scan binary, you can specify a data file on the
command line which contains the transponder frequencies. Here
is a sample file for the above channel transponders:
# Data file for DVB scan program
#
# C Frequency SymbolRate FEC QAM
# S Frequency Polarisation SymbolRate FEC
# T Frequency Bandwidth FEC FEC2 QAM Mode Guard Hier
T 226500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
T 191625000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
T 219500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
T 177500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
T 536500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
The defaults for the transponder frequency and other
modulation parameters were obtained from www.dba.org.au.
When Scan runs, it will output channels.conf information for
any channel's transponders which the card's frontend can lock
onto. (i.e. any whose signal is strong enough at your
antenna).
Here's my channels.conf file for anyone who's interested:
ABC HDTV:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64
:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:2307:0:560
ABC TV Melbourne:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_
4:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:65
0:561
ABC TV 2:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64
:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:562
ABC TV 3:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64
:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:563
ABC TV 4:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64
:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:564
ABC DiG Radio:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:Q
AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:0:2311:56
6
TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM
_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:158
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TEN Digital 1:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:Q
AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1
586
TEN Digital 2:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:Q
AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1
587
TEN Digital 3:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:Q
AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1
588
TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM
_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:158
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TEN Digital 4:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:Q
AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1
590
TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM
_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:159
1
TEN HD:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:T
RANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:514:0:1592
TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM
_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:159
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Nine Digital:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QA
M_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:513:660:10
72
Nine Digital HD:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2
:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:0:1
073
Nine Guide:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_
64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:514:670:1074
7 Digital:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_6
4:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1328
7 Digital 1:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM
_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1329
7 Digital 2:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM
_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1330
7 Digital 3:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM
_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1331
7 HD Digital:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QA
M_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:833:834:133
2
7 Program Guide:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3
:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:865:866:
1334
SBS HD:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:T
RANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:102:103:784
SBS DIGITAL 1:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:Q
AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:161:81:785
SBS DIGITAL 2:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:Q
AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:162:83:786
SBS EPG:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:
TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:163:85:787
SBS RADIO 1:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM
_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:0:201:798
SBS RADIO 2:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM
_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:0:202:799
_________________________________________________________
Known Limitations
At present I can say with confidence that the frontend tunes
via /dev/dvb/adapter{x}/frontend0 and supplies an MPEG2 stream
via /dev/dvb/adapter{x}/dvr0. I have not tested the
functionality of any other part of the card yet. I will do so
over time and update this document.
There are some limitations in the i2c layer due to a returned
error message inconsistency. Although this generates errors in
dmesg and the system logs, it does not appear to affect the
ability of the frontend to function correctly.
_________________________________________________________
Further Update
dvbstream and VideoLAN Client on windows works a treat with
DVB, in fact this is currently serving as my main way of
viewing DVB-T at the moment. Additionally, VLC is happily
decoding HDTV signals, although the PC is dropping the odd
frame here and there - I assume due to processing capability -
as all the decoding is being done under windows in software.
Many thanks to Nigel Pearson for the updates to this document
since the recent revision of the driver.
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