305 строки
14 KiB
Plaintext
305 строки
14 KiB
Plaintext
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HOWTO: Get An Avermedia DVB-T working under Linux
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______________________________________________
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Table of Contents
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Assumptions and Introduction
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The Avermedia DVB-T
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Getting the card going
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Receiving DVB-T in Australia
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Known Limitations
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Further Update
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Assumptions and Introduction
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It is assumed that the reader understands the basic structure
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of the Linux Kernel DVB drivers and the general principles of
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Digital TV.
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One significant difference between Digital TV and Analogue TV
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that the unwary (like myself) should consider is that,
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although the component structure of budget DVB-T cards are
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substantially similar to Analogue TV cards, they function in
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substantially different ways.
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The purpose of an Analogue TV is to receive and display an
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Analogue Television signal. An Analogue TV signal (otherwise
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known as composite video) is an analogue encoding of a
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sequence of image frames (25 per second) rasterised using an
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interlacing technique. Interlacing takes two fields to
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represent one frame. Computers today are at their best when
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dealing with digital signals, not analogue signals and a
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composite video signal is about as far removed from a digital
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data stream as you can get. Therefore, an Analogue TV card for
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a PC has the following purpose:
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* Tune the receiver to receive a broadcast signal
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* demodulate the broadcast signal
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* demultiplex the analogue video signal and analogue audio
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signal (note some countries employ a digital audio signal
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embedded within the modulated composite analogue signal -
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NICAM.)
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* digitize the analogue video signal and make the resulting
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datastream available to the data bus.
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The digital datastream from an Analogue TV card is generated
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by circuitry on the card and is often presented uncompressed.
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For a PAL TV signal encoded at a resolution of 768x576 24-bit
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color pixels over 25 frames per second - a fair amount of data
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is generated and must be proceesed 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 PC's have onboard MPEG2 encoders which permit the raw
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digital data stream to be presented to the PC in an encoded
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and compressed form - similar to the form that is used in
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Digital TV.
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The purpose of a simple budget digital TV card (DVB-T,C or S)
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is to simply:
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* Tune the received to receive a broadcast signal.
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* Extract the encoded digital datastream from the broadcast
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signal.
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* Make the encoded digital datastream (MPEG2) available to
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the data bus.
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The significant difference between the two is that the tuner
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on the analogue TV card spits out an Analogue signal, whereas
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the tuner on the digital TV card spits out a compressed
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encoded digital datastream. As the signal is already
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digitised, it is trivial to pass this datastream to the PC
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databus with minimal additional processing and then extract
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the digital video and audio datastreams passing them to the
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appropriate software or hardware for decoding and viewing.
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_________________________________________________________
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The Avermedia DVB-T
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The Avermedia DVB-T is a budget PCI DVB card. It has 3 inputs:
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* RF Tuner Input
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* Composite Video Input (RCA Jack)
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* SVIDEO Input (Mini-DIN)
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The RF Tuner Input is the input to the tuner module of the
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card. The Tuner is otherwise known as the "Frontend" . The
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Frontend of the Avermedia DVB-T is a Microtune 7202D. A timely
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post to the linux-dvb mailing list ascertained that the
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Microtune 7202D is supported by the sp887x driver which is
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found in the dvb-hw CVS module.
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The DVB-T card is based around the BT878 chip which is a very
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common multimedia bridge and often found on Analogue TV cards.
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There is no on-board MPEG2 decoder, which means that all MPEG2
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decoding must be done in software, or if you have one, on an
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MPEG2 hardware decoding card or chipset.
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_________________________________________________________
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Getting the card going
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In order to fire up the card, it is necessary to load a number
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of modules from the DVB driver set. Prior to this it will have
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been necessary to download these drivers from the linuxtv CVS
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server and compile them successfully.
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Depending on the card's feature set, the Device Driver API for
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DVB under Linux will expose some of the following device files
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in the /dev tree:
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* /dev/dvb/adapter0/audio0
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* /dev/dvb/adapter0/ca0
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* /dev/dvb/adapter0/demux0
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* /dev/dvb/adapter0/dvr0
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* /dev/dvb/adapter0/frontend0
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* /dev/dvb/adapter0/net0
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* /dev/dvb/adapter0/osd0
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* /dev/dvb/adapter0/video0
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The primary device nodes that we are interested in (at this
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stage) for the Avermedia DVB-T are:
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* /dev/dvb/adapter0/dvr0
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* /dev/dvb/adapter0/frontend0
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The dvr0 device node is used to read the MPEG2 Data Stream and
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the frontend0 node is used to tune the frontend tuner module.
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At this stage, it has not been able to ascertain the
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functionality of the remaining device nodes in respect of the
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Avermedia DVBT. However, full functionality in respect of
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tuning, receiving and supplying the MPEG2 data stream is
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possible with the currently available versions of the driver.
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It may be possible that additional functionality is available
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from the card (i.e. viewing the additional analogue inputs
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that the card presents), but this has not been tested yet. If
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I get around to this, I'll update the document with whatever I
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find.
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To power up the card, load the following modules in the
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following order:
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* insmod dvb-core.o
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* modprobe bttv.o
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* insmod bt878.o
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* insmod dvb-bt8xx.o
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* insmod sp887x.o
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Insertion of these modules into the running kernel will
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activate the appropriate DVB device nodes. It is then possible
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to start accessing the card with utilities such as scan, tzap,
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dvbstream etc.
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The frontend module sp887x.o, requires an external firmware.
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Please use the command "get_dvb_firmware sp887x" to download
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it. Then copy it to /usr/lib/hotplug/firmware.
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Receiving DVB-T in Australia
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I have no experience of DVB-T in other countries other than
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Australia, so I will attempt to explain how it works here in
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Melbourne and how this affects the configuration of the DVB-T
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card.
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The Digital Broadcasting Australia website has a Reception
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locatortool which provides information on transponder channels
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and frequencies. My local transmitter happens to be Mount
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Dandenong.
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The frequencies broadcast by Mount Dandenong are:
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Table 1. Transponder Frequencies Mount Dandenong, Vic, Aus.
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Broadcaster Channel Frequency
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ABC VHF 12 226.5 MHz
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TEN VHF 11 219.5 MHz
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NINE VHF 8 191.625 MHz
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SEVEN VHF 6 177.5 MHz
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SBS UHF 29 536.5 MHz
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The Scan utility has a set of compiled-in defaults for various
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countries and regions, but if they do not suit, or if you have
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a pre-compiled scan binary, you can specify a data file on the
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command line which contains the transponder frequencies. Here
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is a sample file for the above channel transponders:
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# Data file for DVB scan program
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#
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# C Frequency SymbolRate FEC QAM
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# S Frequency Polarisation SymbolRate FEC
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# T Frequency Bandwidth FEC FEC2 QAM Mode Guard Hier
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T 226500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
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T 191625000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
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T 219500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
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T 177500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
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T 536500000 7MHz 2/3 NONE QAM64 8k 1/8 NONE
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The defaults for the transponder frequency and other
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modulation parameters were obtained from www.dba.org.au.
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When Scan runs, it will output channels.conf information for
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any channel's transponders which the card's frontend can lock
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onto. (i.e. any whose signal is strong enough at your
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antenna).
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Here's my channels.conf file for anyone who's interested:
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ABC HDTV:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64
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:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:2307:0:560
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ABC TV Melbourne:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_
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4:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:65
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0:561
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ABC TV 2:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64
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:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:562
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ABC TV 3:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64
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:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:563
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ABC TV 4:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:QAM_64
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:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:564
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ABC DiG Radio:226500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_3_4:Q
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AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:0:2311:56
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6
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TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM
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_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:158
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5
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TEN Digital 1:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:Q
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AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1
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586
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TEN Digital 2:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:Q
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AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1
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587
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TEN Digital 3:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:Q
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AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1
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588
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TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM
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_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:158
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9
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TEN Digital 4:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:Q
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AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:1
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590
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TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM
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_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:159
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1
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TEN HD:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_64:T
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RANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:514:0:1592
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TEN Digital:219500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM
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_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:650:159
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3
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Nine Digital:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QA
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M_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:513:660:10
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72
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Nine Digital HD:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2
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:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:512:0:1
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073
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Nine Guide:191625000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_3_4:FEC_1_2:QAM_
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64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_16:HIERARCHY_NONE:514:670:1074
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7 Digital:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_6
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4:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1328
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7 Digital 1:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM
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_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1329
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7 Digital 2:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM
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_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1330
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7 Digital 3:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM
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_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:769:770:1331
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7 HD Digital:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QA
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M_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:833:834:133
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2
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7 Program Guide:177500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3
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:QAM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:865:866:
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1334
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SBS HD:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:T
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RANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:102:103:784
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SBS DIGITAL 1:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:Q
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AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:161:81:785
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SBS DIGITAL 2:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:Q
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AM_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:162:83:786
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SBS EPG:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM_64:
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TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:163:85:787
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SBS RADIO 1:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM
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_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:0:201:798
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SBS RADIO 2:536500000:INVERSION_OFF:BANDWIDTH_7_MHZ:FEC_2_3:FEC_2_3:QAM
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_64:TRANSMISSION_MODE_8K:GUARD_INTERVAL_1_8:HIERARCHY_NONE:0:202:799
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_________________________________________________________
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Known Limitations
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At present I can say with confidence that the frontend tunes
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via /dev/dvb/adapter{x}/frontend0 and supplies an MPEG2 stream
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via /dev/dvb/adapter{x}/dvr0. I have not tested the
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functionality of any other part of the card yet. I will do so
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over time and update this document.
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There are some limitations in the i2c layer due to a returned
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error message inconsistency. Although this generates errors in
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dmesg and the system logs, it does not appear to affect the
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ability of the frontend to function correctly.
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_________________________________________________________
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Further Update
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dvbstream and VideoLAN Client on windows works a treat with
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DVB, in fact this is currently serving as my main way of
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viewing DVB-T at the moment. Additionally, VLC is happily
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decoding HDTV signals, although the PC is dropping the odd
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frame here and there - I assume due to processing capability -
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as all the decoding is being done under windows in software.
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Many thanks to Nigel Pearson for the updates to this document
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since the recent revision of the driver.
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January 29th 2004
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