path: root/dvb-spec/dvbapi/frontend.tex

\devsec{DVB Frontend API}

The DVB frontend device controls the tuner and DVB demodulator hardware.
It can be accessed through \texttt{/dev/ost/frontend}.
If you are using \texttt{devfs} you can use \texttt{/dev/dvb/card0/frontend}.
The frontend device will only be made visible through \texttt{devfs}
if the corresponding card actually has a frontend. Cards which support
the DVB API but, e.g., only can play back recordings, will not offer the 
frontend device.

\devsubsec{Frontend Data Types}

\devsubsubsec{frontend status}
\label{frontendstatus}

Several functions of the frontend device use the feStatus data 
type defined by
\begin{verbatim}
typedef uint32_t feStatus;
\end{verbatim}
to indicate the current state and/or state changes of 
the frontend hardware. 

\noindent
It can take on the values
\begin{verbatim}
#define FE_HAS_POWER         1
#define FE_HAS_SIGNAL        2
#define FE_SPECTRUM_INV      4
#define FE_HAS_LOCK          8
#define FE_HAS_CARRIER      16
#define FE_HAS_VITERBI      32
#define FE_HAS_SYNC         64
#define TUNER_HAS_LOCK     128
\end{verbatim}
which can be ORed together and have the following meaning:

\medskip

\begin{tabular}{lp{11cm}}
FE\_HAS\_POWER & the frontend is powered up and is ready to be used\\
FE\_HAS\_SIGNAL & the frontend detects a signal above the normal noise level\\
FE\_SPECTRUM\_INV & spectrum inversion is enabled/was necessary for lock\\
FE\_HAS\_LOCK & frontend successfully locked to a DVB signal \\
FE\_HAS\_CARRIER & carrier detected in signal\\
FE\_HAS\_VITERBI & lock at viterbi decoder stage\\
FE\_HAS\_SYNC    & TS sync bytes detected \\
TUNER\_HAS\_LOCK & the tuner has a frequency lock
\end{tabular}


\devsubsubsec{frontend parameters}
\label{frontendparameters}

The kind of parameters passed to the frontend device for tuning 
depend on the kind of hardware you are using.
All kinds of parameters are combined as a union in the 
FrontendParameters structure:
\begin{verbatim}
typedef struct {
        __u32 Frequency;        /* (absolute) frequency in Hz for QAM/OFDM */
                                /* intermediate frequency in kHz for QPSK */
        fe_spectral_inversion_t Inversion;    /* spectral inversion */
        union {
                QPSKParameters qpsk;
                QAMParameters  qam;
                OFDMParameters ofdm;
        } u;
} FrontendParameters;
\end{verbatim}

For satellite QPSK frontends you have to use QPSKParameters defined by
\begin{verbatim}
typedef struct {
        __u32    SymbolRate; /* symbol rate in Symbols per second */
        fe_code_rate_t FEC_inner;  /* forward error correction (see above) */
} QPSKParameters;
\end{verbatim}
for cable QAM frontend you use the QAMParameters structure
\begin{verbatim}
typedef struct {
        __u32      SymbolRate; /* symbol rate in Symbols per second */
        fe_code_rate_t   FEC_outer;  /* forward error correction (see above) */
        fe_code_rate_t   FEC_inner;  /* forward error correction (see above) */
        fe_modulation_t QAM;        /* modulation type (see above) */
} QAMParameters;
\end{verbatim}
DVB-T frontends are supported by the OFDMParamters structure
\begin{verbatim}
typedef struct {
        fe_bandwidth_t     bandWidth;
        fe_code_rate_t      HP_fe_code_rate_t;          /* high priority stream code rate */
        fe_code_rate_t      LP_fe_code_rate_t;          /* low priority stream code rate */
        fe_modulation_t    Constellation;        /* modulation type (see above) */
        fe_transmit_mode_t  TransmissionMode;
        fe_guard_interval_t guardInterval;
        fe_hierarchy_t     fe_hierarchy_tInformation;
} OFDMParameters;
\end{verbatim}

In the case of QPSK frontends the Frequency field specifies the intermediate  
frequency, i.e. the offset which is effectively added to the local oscillator 
frequency (LOF) of the LNB.
The intermediate frequency has to be specified in units of kHz.
For QAM and OFDM frontends the Frequency specifies the absolute frequency
and is given in Hz.

The Inversion field can take one of these values:
\begin{verbatim}
typedef enum {
        INVERSION_OFF,
        INVERSION_ON,
        INVERSION_AUTO
} fe_spectral_inversion_t;
\end{verbatim}
It indicates if spectral inversion should be presumed or not. 
In the automatic setting (\verb INVERSION\_AUTO) the hardware will
try to figure out the correct setting by itself.

\noindent
The possible values for the FEC\_inner field are
\begin{verbatim}
enum {
        FEC_AUTO, 
        FEC_1_2,
        FEC_2_3,
        FEC_3_4,
        FEC_5_6,
        FEC_7_8,
        FEC_NONE
};
\end{verbatim}
which correspond to error correction rates of $1\over 2$, $2\over 3$, etc.,
no error correction or auto detection.

\noindent 
For cable and terrestrial frontends (QAM and OFDM) one also has to 
specify the quadrature modulation mode which can be one of the following:
\begin{verbatim}
typedef enum
{       QPSK,
        QAM_16,
        QAM_32,
        QAM_64,
        QAM_128,
        QAM_256
} QAM_TYPE;
\end{verbatim}

Finally, there are several more parameters for OFDM:
\begin{verbatim}
typedef enum {
        TRANSMISSION_MODE_2K,
        TRANSMISSION_MODE_8K
} fe_transmit_mode_t;
\end{verbatim}

\begin{verbatim}
typedef enum {
        BANDWIDTH_8_MHZ,
        BANDWIDTH_7_MHZ,
        BANDWIDTH_6_MHZ
} fe_bandwidth_t;
\end{verbatim}

\begin{verbatim}
typedef enum {
        GUARD_INTERVAL_1_32,
        GUARD_INTERVAL_1_16,
        GUARD_INTERVAL_1_8,
        GUARD_INTERVAL_1_4
} fe_guard_interval_t;
\end{verbatim}

\begin{verbatim}
typedef enum {
        HIERARCHY_NONE,
        HIERARCHY_1,
        HIERARCHY_2,
        HIERARCHY_4
} fe_hierarchy_t;
\end{verbatim}


\devsubsubsec{frontend events}
\label{frontendevents}

\begin{verbatim}
enum {
        FE_UNEXPECTED_EV,
        FE_COMPLETION_EV,
        FE_FAILURE_EV 
};
\end{verbatim}

\begin{verbatim}
typedef struct {
        EventType type; /* type of event, FE_UNEXPECTED_EV, ... */
        long timestamp; /* time in seconds since 1970-01-01 */

        union {
                struct {
                        fe_status_t previousStatus; /* status before event */
                        fe_status_t currentStatus;  /* status during event */
                } unexpectedEvent;
                FrontendParameters completionEvent;    /* parameters for which the
                                                          tuning succeeded */
                fe_status_t failureEvent;           /* status at failure (e.g. no lock) */
        } u;
} FrontendEvent;
\end{verbatim}

\begin{verbatim}
struct qpskRegister {
        uint8_t chipId;
        uint8_t address;
        uint8_t value;
};
\end{verbatim}

\begin{verbatim}
struct qamRegister {
        uint8_t chipId;
        uint8_t address;
        uint8_t value;
};
\end{verbatim}

\begin{verbatim}
struct qpskFrontendInfo {
        uint32_t minFrequency;
        uint32_t maxFrequency;
        uint32_t maxSymbolRate;
        uint32_t minSymbolRate;
        uint32_t hwType;
        uint32_t hwVersion;
};
\end{verbatim}

\begin{verbatim}
struct qamFrontendInfo {
        uint32_t minFrequency;
        uint32_t maxFrequency;
        uint32_t maxSymbolRate;
        uint32_t minSymbolRate;
        uint32_t hwType;
        uint32_t hwVersion;
};
\end{verbatim}

\begin{verbatim}
typedef enum {
        FE_POWER_ON, 
        FE_POWER_STANDBY, 
        FE_POWER_SUSPEND, 
        FE_POWER_OFF
} powerState_t;
\end{verbatim}


\clearpage


\devsubsec{Frontend Function Calls}

\function{open()}{
  int open(const char *deviceName, int flags);}{
  This system call opens a named frontend device (e.g. /dev/ost/qpskfe
  for a satellite frontend or /dev/ost/qamfe for a cable frontend) 
  for subsequent use.

  The device can be opened in read-only mode, which only allows
  monitoring of device status and statistics, or read/write mode, which allows 
  any kind of use (e.g. performing tuning operations.)
  
  In a system with multiple front-ends, it is usually the case that multiple
  devices cannot be open in read/write mode simultaneously.  As long as a 
  front-end device is opened in read/write mode, other open() calls in 
  read/write mode will either fail or block, depending on whether 
  non-blocking or blocking mode was specified.
  A front-end device opened in blocking mode can later be put into non-blocking
  mode (and vice versa) using the F\_SETFL command of the fcntl system call.
  This is a standard system call, documented in the Linux manual page for fcntl.
  When an open() call has succeeded, the device will be ready for use in the 
  specified mode. This implies that the corresponding hardware is powered up, 
  and that other front-ends may have been powered down to make that possible.
  
  }{
  const char *deviceName & Name of specific video device.\\
  int flags & A bit-wise OR of the following flags:\\
            & \hspace{1em} O\_RDONLY read-only access\\
            & \hspace{1em} O\_RDWR read/write access\\
            & \hspace{1em} O\_NONBLOCK open in non-blocking mode \\
            & \hspace{1em} (blocking mode is the default)\\
  }{
  ENODEV    & Device driver not loaded/available.\\
  EINTERNAL & Internal error.\\
  EBUSY     & Device or resource busy.\\
  EINVAL    & Invalid argument.\\
}

\function{close()}{
  int close(int fd);}{
  This system call closes a previously opened front-end device.  
  After closing a front-end device, its corresponding hardware might be
  powered down automatically, but only when this is needed to open 
  another front-end device.
  To affect an unconditional power down, it should be done explicitly using 
  the OST\_SET\_POWER\_STATE ioctl.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  }{
  EBADF & fd is not a valid open file descriptor.\\
}

\ifunction{OST\_SELFTEST}{
  int ioctl(int fd, int request = OST\_SELFTEST);}{
  This ioctl call initiates an automatic self-test of the front-end hardware.  
  This call requires read/write access to the device.
  }{
  int fd      & File descriptor returned by a previous call to open().\\
  int request & Equals OST\_SELFTEST for this command.\\
  }{
  -1& Self test failure.\\
}

\ifunction{OST\_SET\_POWER\_STATE}{
  int ioctl(int fd, int request = OST\_SET\_POWER\_STATE, uint32\_t state);}{
  This ioctl call, implemented in many OST device drivers, enables direct 
  control over the power state of the hardware device, which may be on, off, 
  standby, or suspend.  The latter two are low-power modes, which disable all 
  functionality of the device until turned on again. In contrast to the off 
  state, however, the standby and suspend states resume operation in the same
  state as when the device was active.  The only difference between the standby
  and suspend states is a different tradeoff between resume time and power 
  consumption. Power consumption may be lower in the suspend state at the
  cost of a longer resume time.\\
  A device that implements this call does not necessarily support two low-power
  modes. If it only supports one low-power state, or none at all, the 
  OST\_SET\_POWER\_STATE operation for the missing states will 
  still succeed, but 
  it will be mapped to an existing state as per this table: \\
  \begin{center}
  \begin{tabular}[h]{cll}
    number of low-power & requested state & resulting state\\
    states supported &&\\
    \\
    1 & standby & suspend \\
    1 & suspend & suspend \\
    0 & standby & on \\
    0 & suspend & on
  \end{tabular}
  \end{center}\\
  For other cases where a required state is missing, an error code will be
  returned.  This can happen if a device does not support the power-off state, 
  but nevertheless implements this ioctl operation for control of low-power 
  states.
  When opening a device in read/write mode, the driver ensures that the 
  corresponding hardware device is turned on initially.  If the device is 
  later turned off or put in suspend mode, it has to be explicitly turned on 
  again.\\
  This call requires read/write access to the device.  (Note that the power 
  management driver can affect the power state of devices without using this 
  ioctl operation, so having exclusive read/write access to a device does not 
  imply total control over the power state.)
  }{
  int fd      & File descriptor returned by a previous call to open().\\
  int request & Equals OST\_SET\_POWER\_STATE for this command.\\
  uint32\_t state & Requested power state.  One of: \\
  &
  \begin{tabular}[h]{ll}
  OST\_POWER\_ON&           turn power on\\
  OST\_POWER\_STANDBY&      set device in standby mode\\
  OST\_POWER\_SUSPEND&     set device in suspend mode\\
  OST\_POWER\_OFF&       turn power off\\
  \end{tabular}
  }{
  EBADF& fd is not a valid open file descriptor.\\
  EINVAL& Illegal state, or not available on this device.\\
  EPERM & Permission denied (needs read/write access).\\
  ENOSYS& Function not available for this device.
}

\ifunction{FE\_GET\_POWER\_STATE}{
  int ioctl(int fd, int request = OST\_GET\_POWER\_STATE, uint32\_t *state);}{
  This ioctl call, implemented in many OST device drivers, obtains the power
  state of the hardware device, which may be on, off, standby, or suspend.
  A device that implements this call does not necessarily support all four states.
  If there is only one low-power state, the suspend state will be returned for 
  that state.  If there is no low-power state, the on state will be reported 
  standby and suspend states will be equivalent to the on state.
  For this command, read-only access to the device is sufficient.
  }{
  int fd      & File descriptor returned by a previous call to open().\\
  int request & Equals OST\_GET\_POWER\_STATE for this command.\\
  uint32\_t *state & Requested power state.  One of: \\
  &
  \begin{tabular}[h]{ll}
  OST\_POWER\_ON&        power is on\\
  OST\_POWER\_STANDBY&   device in standby mode\\
  OST\_POWER\_SUSPEND&   device in suspend mode\\
  OST\_POWER\_OFF&       power is off\\
  \end{tabular}
  }{
  EBADF& fd is not a valid open file descriptor.\\
  EINVAL& Illegal state, or not available on this device.\\
  EFAULT& state points to invalid address.\\
  ENOSYS& Function not available for this device.
}

\ifunction{FE\_READ\_STATUS}{
  int ioctl(int fd, int request = FE\_READ\_STATUS, feStatus *status);}{
  This ioctl call returns status information about the front-end.
  This call only requires read-only access to the device.
  }{
  int fd      & File descriptor returned by a previous call to open().\\
  int request & Equals FE\_READ\_STATUS for this command.\\
  struct feStatus *status&Points to the location where the front-end
  status word is to be stored.
  }{
  EBADF& fd is not a valid open file descriptor.\\
  EFAULT& status points to invalid address.\\
}

\ifunction{FE\_READ\_BER}{
  int ioctl(int fd, int request = FE\_READ\_BER, uint32\_t *ber);}{
  This ioctl call returns the bit error rate for the signal currently 
  received/demodulated by the front-end. For this command, read-only access 
  to the device is sufficient.
  }{
  int fd      & File descriptor returned by a previous call to open().\\
  int request & Equals FE\_READ\_BER for this command.\\
  uint32\_t *ber & The bit error rate, as a multiple of $10^{-9}$, 
                   is stored into *ber.\\
                 & Example: a value of 2500 corresponds to a bit error 
                   rate of $2.5\cdot 10^{-6}$, or 1 error in 400000 bits.
  }{
  EBADF& fd is not a valid open file descriptor.\\
  EFAULT& ber points to invalid address.\\
  ENOSIGNAL& There is no signal, thus no meaningful bit error
             rate.  Also returned if the front-end is not turned on.\\
  ENOSYS&         Function not available for this device.
}

\ifunction{FE\_READ\_SNR}{
  int ioctl(int fd, int request = FE\_READ\_SNR, int32\_t *snr);}{
  This ioctl call returns the signal-to-noise ratio for the signal currently 
  received by the front-end. For this command, read-only access to the device
  is sufficient.
  }{
  int fd      & File descriptor returned by a previous call to open().\\
  int request & Equals FE\_READ\_SNR for this command.\\
  int32\_t *snr& The signal-to-noise ratio, as a multiple of
                $10^{-6}$ dB, is stored into *snr.\\
              & Example: a value of 12,300,000 corresponds
                to a signal-to-noise ratio of 12.3 dB.
}{
  EBADF& fd is not a valid open file descriptor.\\
  EFAULT& snr points to invalid address.\\
  ENOSIGNAL&        There is no signal, thus no meaningful signal
  strength value.  Also returned if front-end is not  turned on.\\
  ENOSYS&         Function not available for this device.
}

\ifunction{FE\_READ\_SIGNAL\_STRENGTH}{
  int ioctl( int fd, int request = FE\_READ\_SIGNAL\_STRENGTH, int32\_t *strength);
}{
This ioctl call returns the signal strength value for the signal currently 
received by the front-end. For this command, read-only access to the device 
is sufficient.
}{
int fd      & File descriptor returned by a previous call to open().\\
int request & Equals FE\_READ\_SIGNAL\_STRENGTH for this command.\\
int32\_t *strength & The signal strength value, as a multiple of 
                    $10^{-6 }$ dBm,
                    is stored into *strength.  \\
                    &Example: a value of -12,500,000 corresponds to a signal
                    strength value of -12.5 dBm.
}{
  EBADF& fd is not a valid open file descriptor.\\
  EFAULT& status points to invalid address.\\
  ENOSIGNAL&        There is no signal, thus no meaningful signal
  strength value.  Also returned if front-end is not  turned on.\\
  ENOSYS&         Function not available for this device.
}

\ifunction{FE\_READ\_UNCORRECTED\_BLOCKS}{
  int ioctl( int fd, int request = FE\_READ\_UNCORRECTED\_BLOCKS, uint32\_t *ublocks);  }{
  This ioctl call returns the number of uncorrected blocks detected by 
  the device driver during its lifetime.
  For meaningful measurements, the increment in 
  block count during a specific time interval should be calculated. 
  For this command, read-only access to the device is sufficient.\\
  Note that the counter will wrap to zero after its maximum count has 
  been reached.
}{
int fd      & File descriptor returned by a previous call to open().\\
int request & Equals FE\_READ\_UNCORRECTED\_BLOCKS for this command.\\
uint32\_t *ublocks & The total number of uncorrected blocks seen
by the driver so far.
}{
  EBADF& fd is not a valid open file descriptor.\\
  EFAULT& ublocks points to invalid address.\\
  ENOSYS&         Function not available for this device.
}


\ifunction{FE\_GET\_NEXT\_FREQUENCY}{
  int ioctl( int fd, int request = FE\_GET\_NEXT\_FREQUENCY, uint32\_t *freq);}{
  When scanning a frequency range, it is desirable to use a scanning step size 
  that is as large as possible, yet small enough to be able to lock to any signal 
  within the range.
  This  ioctl operation does just that - it increments a given frequency by a 
  step size suitable for efficient scanning.
  The step size used by this function may be a quite complex function of the given
  frequency, hardware capabilities, and parameter settings of the device.  Thus, a
  returned result is only valid for the current state of the device.
  For this command, read-only access to the device is sufficient.\\
  Note that scanning may still be excruciatingly slow on some hardware, for 
  other reasons than a non-optimal scanning step size.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals  FE\_GET\_NEXT\_FREQUENCY for this command.\\
  uint32\_t *freq& Input: a given frequency \\
  & Output: the frequency corresponding to
                 the next higher frequency setting.\\
  }{
  EBADF& fd is not a valid open file descriptor.\\
  EFAULT& freq points to invalid address.\\
  EINVAL& Maximum supported frequency reached.\\
  ENOSYS& Function not available for this device.
}

\ifunction{FE\_GET\_NEXT\_SYMBOL\_RATE}{
  int ioctl( int fd, int request = FE\_GET\_NEXT\_SYMBOL\_RATE, uint32\_t *symbolRate);
  }{
  When scanning a range of symbol rates (e.g. for "blind acquisition") it is 
  desirable to use a scanning step size that is as large as possible, yet 
  small enough to detect any valid signal within the range.  This ioctl 
  operation does just that - it increments a given symbol rate by a step size
  suitable for efficient scanning.
  The step size used by this function may be a quite complex function of the given
  symbol rate, hardware capabilities, and parameter settings of the device.  
  Thus, a returned result is only valid for the current state of the device.
  For this command, read-only access to the device is sufficient.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals  FE\_GET\_NEXT\_SYMBOL\_RATE for this command.\\
  uint32\_t *symbolRate& Input: a given symbol rate \\
  & Output: the symbol rate corresponding to
                 the next higher symbol rate.\\
  }{
  EBADF& fd is not a valid open file descriptor.\\
  EFAULT& symbolRate points to invalid address.\\
  EINVAL& Maximum supported symbol rate reached.\\
  ENOSYS& Function not available for this device.
}

\ifunction{FE\_SET\_FRONTEND}{
  int ioctl(int fd, int request = FE\_SET\_FRONTEND, struct FrontendParameters *p);}{
        This ioctl call starts a tuning operation using specified parameters.  
        The result of this call will be successful if the parameters were valid and 
        the tuning could be initiated.
        The result of the tuning operation in itself, however, will arrive 
        asynchronously as an event (see documentation for FE\_GET\_EVENT 
        and FrontendEvent.)
        If a new FE\_SET\_FRONTEND operation is initiated before the previous
        one was completed,
        the previous operation will be aborted in favor of the new one.
        This command requires read/write access to the device.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals FE\_SET\_FRONTEND for this command.\\
  struct FrontendParameters *p& Points to parameters for tuning operation.\\
  }{
  EBADF& fd is not a valid open file descriptor.\\
  EFAULT& p points to invalid address.\\
  EINVAL& Maximum supported symbol rate reached.\\
}

\ifunction{FE\_GET\_EVENT}{
  int ioctl(int fd, int request = QPSK\_GET\_EVENT, struct qpskEvent *ev);}{
  This ioctl call returns an event of type qpskEvent if available. If an event
  is not available, the behavior depends on whether the device is in blocking 
  or non-blocking mode.  In the latter case, the call fails immediately with 
  errno set to EWOULDBLOCK. In the former case, the call blocks until an event
  becomes available.\\
  The standard Linux poll() and/or select() system calls can be used with the 
  device file descriptor to watch for new events.  For select(), the file 
  descriptor should be included in the exceptfds argument, and for poll(), 
  POLLPRI should be specified as the wake-up condition.
  Since the event queue allocated is rather small (room for 8 events), the queue
  must be serviced regularly to avoid overflow.   If an overflow happens, the 
  oldest event is discarded from the queue, and an error (EOVERFLOW) occurs 
  the next time the queue is read. After reporting the error condition in this 
  fashion, subsequent QPSK\_GET\_EVENT calls will return events from the queue as
  usual.\\
  For the sake of implementation simplicity, this command requires read/write 
  access to the device.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals QPSK\_GET\_EVENT for this command.\\
  struct qpskEvent *ev&Points to the location where the event, if any, is to be stored.
  }{
  EBADF& fd is not a valid open file descriptor.\\
  EFAULT& ev points to invalid address.\\
  EWOULDBLOCK &              There is no event pending, and the device is in
                                non-blocking mode.\\
  EOVERFLOW &\\
&   Overflow in event queue - one or more events were lost.\\
}

\ifunction{FE\_GET\_INFO}{
  int ioctl(int fd, int request = FE\_GET\_INFO, struct FrontendInfo *info);}{
  This ioctl call returns information about the front-end.
  This call only requires read-only access to the device.
  }{
  int fd & File descriptor returned by a previous call to open().\\
  int request & Equals FE\_GET\_INFO for this command.\\
  struct qpskFrontendInfo *info & Points to the location where the front-end
  information is to be stored.
  }{
  EBADF& fd is not a valid open file descriptor.\\
  EFAULT& info points to invalid address.\\
}

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