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added docs from old DVB/ tree and an updated valgrind patch

How to determine the API version?

  Check in your configure script for #include <linux/dvb/version.h>,
  include it and check the DVB_API_VERSION #define.

  Currently we use version 3, it will be incremented whenever an API change 
  meets the CVS main branch.

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What is a DVB frontend?

  the term 'frontend' refers to this part of the DVB adapter which receives 
  an MPEG transport stream and will feed it later into the Demultiplexer. 
  Whenever you want to receive MPEG streams via satellite, antenna or cable 
  you have to set up your frontend first.

  When you watch on your DVB card or into your SetTopBox the frontend is usually
  the combination of a demodulator chip and a small silver metal box with the
  HF electronic. Usually the demodulator is built into this metal box.

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What do you have to do to set up your frontend?

  First you should try to determine the type of your frontend.

	#include <linux/dvb/frontend.h>

	struct dvb_frontend_info info;
	int fd;

	if ((fd = open ("/dev/dvb/adapter0/frontend0", O_RDWR)) < 0) {
		perror ("open failed");
		return -1;
	}

	ioctl (fd, FE_GET_INFO, &info);

  Now the info.type field contains either FE_QPSK for a satellite frontend, 
  FE_QAM for a cable frontend or FE_OFDM for a terrestrial frontend.

  The info.name field contains a human readable vendor string of your frontend.
  You might want to show this in your GUI to make support easier. 

  The info struct also contains the frequency limits, frontend capabilities,
  the frequency and symbol rate tolerance the AFC or timing recovery loop can 
  compensate and some fields you are not interested in.

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How to set up a cable or terrestrial frontend?

  Fill a dvb_frontend_parameters struct according to the data in your channel 
  list. For cable frontends, you have to fill the qam field of the union, for 
  terrestrial frontends it's the ofdm field.

  Apply it using the FE_SET_FRONTEND_PARAMETERS ioctl. That's all.

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How to set up a satellite frontend?

  Before you set the frontend parameters you have to setup DiSEqC switches and 
  the LNB. Modern LNB's switch their polarisation depending of the DC component
  of their input (13V for vertical polarisation, 18V for horizontal). When they 
  see a 22kHz signal at their input they switch into the high band and use a 
  somewhat higher intermediate frequency to downconvert the signal.

  When your satellite equipment contains a DiSEqC switch device to switch 
  between different satellites you have to send the according DiSEqC commands, 
  usually command 0x38. Take a look into the DiSEqC spec available at 
  http://www.eutelsat.org/ for the complete list of commands.

  The burst signal is used in old equipments and by cheap satellite A/B 
  switches.

  Voltage, burst and 22kHz tone have to be consistent to the values encoded in 
  the DiSEqC commands.

  The complete sequence to set up switch and LNB according to the DiSEqC spec
  looks like this:

   - stop continous tone
   - setup polarisation voltage
   - wait at least 15ms.
   - send your DiSEqC commands using the FE_DISEQC_SEND_MASTER_CMD ioctl
   - wait another 15ms
   - send burst
   - wait 15ms
   - start the 22kHz tone when you tune to a transponder in the high band

  You can copy'n'paste this code sniplets from szap.c or diseqc.c, both 
  test programs are distributed with the linuxtv DVB driver source. All
  DiSEqC related ioctls are passed to the frontend device filedescriptor.

  Depending on the equipment setup, you may or may not have to repeat the 
  DiSEqC commands (only commands, not the whole sequence) for cascaded devices 
  and can pack committed/uncommitted switch messages. See the DiSEqC spec for
  details.

  In an advanced program, you probably want to send this sequence using an 
  asynchonous thread. Since sleep() and similiar calls are pthread 
  cancellation points, it's really simple to stop a running DiSEqC thread 
  before submitting a new sequence.

  Now you have set up switch and LNB, a valid RF signal of the requested 
  satellite should be at the input of the demodulator.

  Fill a dvb_frontend_parameters struct using the qpsk field in the union and
  apply it using the FE_SET_FRONTEND_PARAMETERS ioctl.

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How do I check the frontend status?

  You can perform a poll()/select() on the frontend file descriptor. Whenever
  one of the frontend status bits toggles the poll returns. Now you can
  submit the FE_GET_EVENT ioctl to receive the new status bits. When you used
  one of the XXX_AUTO parameters you might want to use the event.parameters
  field to determine the correct tuned parameters and update your channel list.

  If you want to simulate the old FE_FAILURE_EV frontend event behaviour you
  should check the FE_TIMEDOUT bit, this will be set when the tuning was not 
  successful within a few seconds.

  When you get a FE_REINIT event the frontend was reinitialized. You should 
  send the DiSEqC sequence again if you use a QPSK frontend.

  The FE_READ_SIGNAL_STRENGTH ioctl will fill the signal strength into the 
  16 LSBs of the passed argument. The signal strength range is from 0 (bad)
  to 65535 (too good to be true).

  FE_READ_SNR returns the signal noise ratio. range 0 (bad) to 65535 (not real).
  For both the signal strength and signal noise ratio a value of about 60-70%
  means a good signal.

  Not all FE_READ_XXX ioctl()s are supported by all hardware. Check the ioctl
  return value, if it's less than 0 this ioctl is not supported.

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What does FE_ENABLE_HIGH_LNB_VOLTAGE?

  some STBs (the dbox2 for example) support somewhat higher LNB voltages than
  13 and 18V. They add about 0.5V to compensate voltage drop on long cables.

  This ioctl is not supported on all boxes. You probably want to show an extra
  menu item in your GUI when this ioctl returns a zero value.

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How to do powermanagement, the FE_SET_POWER_STATE ioctls are gone?

  An open() call on the frontend device powers up and initializes the 
  demodulator and switches on LNB power if necessairy. The DiSEqC bus won't
  be resetted, do this manually if you think you need to.

  Some seconds after the device is closed (and was not opened by a new process) 
  LNB power and the demodulator are shut down into sleep mode.

  You can configure the shutdown timeout using the shutdown_timeout module
  parameter. To disable power management set shutdown_timeout=0.

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