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-------------------------------------------------------------------------------
What has changed since the old Nokia OST API?
file naming:
- /dev/ost directory is now called /dev/dvb
- each DVB adapter has it's own directory /dev/dvb/adapterX
- here you'll find a number of frontend devices /dev/dvb/adapterX/frontendY
- driver header directory is located now in /usr/include/linux/dvb/
- we have a linux/dvb/version.h file, this is included by all headers which
don't use the original OST API anymore
struct naming:
- we follow the kernel naming scheme and try to get the namespace clean,
these changes are mostly syntactical
DiSEqC:
- DiSEqC 2.0 ioctls
- the sec-device is gone, DiSEqC ioctls are passed to the frontend
filedescriptor - this matches the hardware better
- the old secCmdSequence is replaced by lowlevel FE_DISEQC_XXX ioctls,
this allows asynchronous DiSEqC, DiSEqC 2.0 and more flexibility for
cascaded devices and exotic setup
frontend events:
- the event struct is simplified, you get an event now whenever one of the
frontend status bits changes
ioctls:
- FE_SELFTEST is gone, was a noop anyway
- FE_GET_NEXT_FREQUENCY and FE_GET_NEXT_SYMBOL_RATE are gone,
this information can be obtained with FE_GET_INFO
- FE_SET_POWER_STATE is gone, powermanagement is done implicitly by device
open()/close() calls
-------------------------------------------------------------------------------
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.
-------------------------------------------------------------------------------
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.
-------------------------------------------------------------------------------
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.
-------------------------------------------------------------------------------
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.
-------------------------------------------------------------------------------
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.
-------------------------------------------------------------------------------
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.
-------------------------------------------------------------------------------
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.
-------------------------------------------------------------------------------
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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