\devsec{Kernel Demux API}

The kernel demux API 

\devsubsec{Kernel Demux Data Types}

\devsubsubsec{dmx\_success\_t}
\label{dmxsuccesst}

\begin{verbatim}
typedef enum { 
  DMX_OK = 0, /* Received Ok */ 
  DMX_LENGTH_ERROR, /* Incorrect length */ 
  DMX_OVERRUN_ERROR, /* Receiver ring buffer overrun */ 
  DMX_CRC_ERROR, /* Incorrect CRC */ 
  DMX_FRAME_ERROR, /* Frame alignment error */ 
  DMX_FIFO_ERROR, /* Receiver FIFO overrun */ 
  DMX_MISSED_ERROR /* Receiver missed packet */ 
} dmx_success_t; 
\end{verbatim}


\devsubsubsec{TS filter types}
\label{tsfiltertypes}

\begin{verbatim}
/*--------------------------------------------------------------------------*/ 
/* TS packet reception */ 
/*--------------------------------------------------------------------------*/

/* TS filter type for set_type() */

#define TS_PACKET       1   /* send TS packets (188 bytes) to callback (default) */ 
#define TS_PAYLOAD_ONLY 2   /* in case TS_PACKET is set, only send the TS
                               payload (<=184 bytes per packet) to callback */
#define TS_DECODER      4   /* send stream to built-in decoder (if present) */
\end{verbatim}


\devsubsubsec{dmx\_ts\_pes\_t}
\label{dmxtspest}

The structure 
\begin{verbatim}
typedef enum
{
        DMX_TS_PES_AUDIO,   /* also send packets to audio decoder (if it exists) */
        DMX_TS_PES_VIDEO,   /* ... */
        DMX_TS_PES_TELETEXT,
        DMX_TS_PES_SUBTITLE,
        DMX_TS_PES_PCR,
        DMX_TS_PES_OTHER,
} dmx_ts_pes_t;
\end{verbatim}
describes the PES type for filters which write to
a built-in decoder. 
The correspond (and should be kept identical) to the types in 
the demux device.

\begin{verbatim}
struct dmx_ts_feed_s { 
        int is_filtering; /* Set to non-zero when filtering in progress */
        struct dmx_demux_s* parent; /* Back-pointer */
        void* priv; /* Pointer to private data of the API client */ 
        int (*set) (struct dmx_ts_feed_s* feed, 
                    __u16 pid,
                    size_t callback_length, 
                    size_t circular_buffer_size, 
                    int descramble, 
                    struct timespec timeout); 
        int (*start_filtering) (struct dmx_ts_feed_s* feed); 
        int (*stop_filtering) (struct dmx_ts_feed_s* feed); 
        int (*set_type) (struct dmx_ts_feed_s* feed, 
                         int type, 
                         dmx_ts_pes_t pes_type);
};

typedef struct dmx_ts_feed_s dmx_ts_feed_t; 
\end{verbatim}

\begin{verbatim}
/*--------------------------------------------------------------------------*/ 
/* PES packet reception (not supported yet) */
/*--------------------------------------------------------------------------*/ 

typedef struct dmx_pes_filter_s {
        struct dmx_pes_s* parent; /* Back-pointer */ 
        void* priv; /* Pointer to private data of the API client */ 
} dmx_pes_filter_t; 
\end{verbatim}

\begin{verbatim}
typedef struct dmx_pes_feed_s {
        int is_filtering; /* Set to non-zero when filtering in progress */
        struct dmx_demux_s* parent; /* Back-pointer */
        void* priv; /* Pointer to private data of the API client */ 
        int (*set) (struct dmx_pes_feed_s* feed, 
                    __u16 pid,
                    size_t circular_buffer_size, 
                    int descramble, 
                    struct timespec timeout); 
        int (*start_filtering) (struct dmx_pes_feed_s* feed); 
        int (*stop_filtering) (struct dmx_pes_feed_s* feed); 
        int (*allocate_filter) (struct dmx_pes_feed_s* feed, 
                                dmx_pes_filter_t** filter); 
        int (*release_filter) (struct dmx_pes_feed_s* feed, 
                               dmx_pes_filter_t* filter); 
} dmx_pes_feed_t; 
\end{verbatim}


\label{sectionfilter}
\begin{verbatim}
typedef struct { 
        __u8 filter_value [DMX_MAX_FILTER_SIZE]; 
        __u8 filter_mask [DMX_MAX_FILTER_SIZE]; 
        struct dmx_section_feed_s* parent; /* Back-pointer */ 
        void* priv; /* Pointer to private data of the API client */ 
} dmx_section_filter_t;
\end{verbatim}

\begin{verbatim}
struct dmx_section_feed_s { 
        int is_filtering; /* Set to non-zero when filtering in progress */ 
        struct dmx_demux_s* parent; /* Back-pointer */
        void* priv; /* Pointer to private data of the API client */ 
        int (*set) (struct dmx_section_feed_s* feed, 
                    __u16 pid, 
                    size_t circular_buffer_size, 
                    int descramble, 
                    int check_crc); 
        int (*allocate_filter) (struct dmx_section_feed_s* feed, 
                                dmx_section_filter_t** filter); 
        int (*release_filter) (struct dmx_section_feed_s* feed, 
                               dmx_section_filter_t* filter); 
        int (*start_filtering) (struct dmx_section_feed_s* feed); 
        int (*stop_filtering) (struct dmx_section_feed_s* feed); 
};
typedef struct dmx_section_feed_s dmx_section_feed_t; 

/*--------------------------------------------------------------------------*/ 
/* Callback functions */ 
/*--------------------------------------------------------------------------*/ 

typedef int (*dmx_ts_cb) ( __u8 * buffer1, 
                           size_t buffer1_length,
                           __u8 * buffer2, 
                           size_t buffer2_length,
                           dmx_ts_feed_t* source, 
                           dmx_success_t success); 

typedef int (*dmx_section_cb) ( __u8 * buffer1,
                                size_t buffer1_len,
                                __u8 * buffer2, 
                                size_t buffer2_len,
                                dmx_section_filter_t * source,
                                dmx_success_t success);

typedef int (*dmx_pes_cb) ( __u8 * buffer1, 
                            size_t buffer1_len,
                            __u8 * buffer2,
                            size_t buffer2_len,
                            dmx_pes_filter_t* source, 
                            dmx_success_t success); 

/*--------------------------------------------------------------------------*/ 
/* DVB Front-End */
/*--------------------------------------------------------------------------*/ 

typedef enum { 
        DMX_OTHER_FE = 0, 
        DMX_SATELLITE_FE, 
        DMX_CABLE_FE, 
        DMX_TERRESTRIAL_FE, 
        DMX_LVDS_FE, 
        DMX_ASI_FE, /* DVB-ASI interface */
        DMX_MEMORY_FE
} dmx_frontend_source_t; 

typedef struct { 
        /* The following char* fields point to NULL terminated strings */ 
        char* id;                    /* Unique front-end identifier */ 
        char* vendor;                /* Name of the front-end vendor */ 
        char* model;                 /* Name of the front-end model */ 
        struct list_head connectivity_list; /* List of front-ends that can 
                                               be connected to a particular 
                                               demux */ 
        void* priv;     /* Pointer to private data of the API client */ 
        dmx_frontend_source_t source;
} dmx_frontend_t;

/*--------------------------------------------------------------------------*/ 
/* MPEG-2 TS Demux */ 
/*--------------------------------------------------------------------------*/ 

/* 
 * Flags OR'ed in the capabilites field of struct dmx_demux_s. 
 */ 

#define DMX_TS_FILTERING                        1 
#define DMX_PES_FILTERING                       2 
#define DMX_SECTION_FILTERING                   4 
#define DMX_MEMORY_BASED_FILTERING              8    /* write() available */ 
#define DMX_CRC_CHECKING                        16 
#define DMX_TS_DESCRAMBLING                     32 
#define DMX_SECTION_PAYLOAD_DESCRAMBLING        64 
#define DMX_MAC_ADDRESS_DESCRAMBLING            128 
\end{verbatim}

\devsubsubsec{demux\_demux\_t}
\label{demuxdemuxt}

\begin{verbatim}
/* 
 * DMX_FE_ENTRY(): Casts elements in the list of registered 
 * front-ends from the generic type struct list_head
 * to the type * dmx_frontend_t
 *. 
*/

#define DMX_FE_ENTRY(list) list_entry(list, dmx_frontend_t, connectivity_list) 

struct dmx_demux_s { 
        /* The following char* fields point to NULL terminated strings */ 
        char* id;                    /* Unique demux identifier */ 
        char* vendor;                /* Name of the demux vendor */ 
        char* model;                 /* Name of the demux model */ 
        __u32 capabilities;          /* Bitfield of capability flags */ 
        dmx_frontend_t* frontend;    /* Front-end connected to the demux */ 
        struct list_head reg_list;   /* List of registered demuxes */
        void* priv;                  /* Pointer to private data of the API client */ 
        int users;                   /* Number of users */
        int (*open) (struct dmx_demux_s* demux); 
        int (*close) (struct dmx_demux_s* demux); 
        int (*write) (struct dmx_demux_s* demux, const char* buf, size_t count); 
        int (*allocate_ts_feed) (struct dmx_demux_s* demux, 
                                 dmx_ts_feed_t** feed, 
                                 dmx_ts_cb callback); 
        int (*release_ts_feed) (struct dmx_demux_s* demux, 
                                dmx_ts_feed_t* feed); 
        int (*allocate_pes_feed) (struct dmx_demux_s* demux, 
                                  dmx_pes_feed_t** feed, 
                                  dmx_pes_cb callback); 
        int (*release_pes_feed) (struct dmx_demux_s* demux, 
                                 dmx_pes_feed_t* feed); 
        int (*allocate_section_feed) (struct dmx_demux_s* demux, 
                                      dmx_section_feed_t** feed, 
                                      dmx_section_cb callback); 
        int (*release_section_feed) (struct dmx_demux_s* demux,
                                     dmx_section_feed_t* feed); 
        int (*descramble_mac_address) (struct dmx_demux_s* demux, 
                                       __u8* buffer1, 
                                       size_t buffer1_length, 
                                       __u8* buffer2, 
                                       size_t buffer2_length,
                                       __u16 pid); 
        int (*descramble_section_payload) (struct dmx_demux_s* demux,
                                           __u8* buffer1, 
                                           size_t buffer1_length,
                                           __u8* buffer2, size_t buffer2_length,
                                           __u16 pid); 
        int (*add_frontend) (struct dmx_demux_s* demux, 
                             dmx_frontend_t* frontend); 
        int (*remove_frontend) (struct dmx_demux_s* demux,
                                dmx_frontend_t* frontend); 
        struct list_head* (*get_frontends) (struct dmx_demux_s* demux); 
        int (*connect_frontend) (struct dmx_demux_s* demux, 
                                 dmx_frontend_t* frontend); 
        int (*disconnect_frontend) (struct dmx_demux_s* demux); 

   
        /* added because js cannot keep track of these himself */
        int (*get_pes_pids) (struct dmx_demux_s* demux, __u16 *pids);
}; 
typedef struct dmx_demux_s dmx_demux_t; 
\end{verbatim}


\devsubsubsec{Demux directory}
\label{demuxdir}

\begin{verbatim}
/* 
 * DMX_DIR_ENTRY(): Casts elements in the list of registered 
 * demuxes from the generic type struct list_head* to the type dmx_demux_t
 *. 
 */ 

#define DMX_DIR_ENTRY(list) list_entry(list, dmx_demux_t, reg_list)

int dmx_register_demux (dmx_demux_t* demux); 
int dmx_unregister_demux (dmx_demux_t* demux); 
struct list_head* dmx_get_demuxes (void); 
\end{verbatim}

\clearpage

\devsubsec{Demux Directory API}

The demux directory is a Linux kernel-wide facility for registering and 
accessing the MPEG-2 TS demuxes in the system. Run-time registering and 
unregistering of demux drivers is possible using this API. 

All demux drivers in the directory implement the abstract interface dmx\_demux\_t.

\kifunction{dmx\_register\_demux()}{
  int dmx\_register\_demux ( dmx\_demux\_t *demux )
  }{
  This function makes a demux driver interface available to the Linux kernel. 
  It is usually called by the init\_module() function of the kernel module that
  contains the demux driver. The caller of this function is responsible for 
  allocating dynamic or static memory for the demux structure and for initializing
  its fields before calling this function. 
  The memory allocated for the demux structure must not be freed before calling
  dmx\_unregister\_demux(),
  }{
  dmx\_demux\_t* demux & Pointer to the demux structure.
  }{
  0 & The function was completed without errors.\\
  -EEXIST   & A demux with the same value of the id field
             already stored in the directory.\\
  -ENOSPC   & No space left in the directory.
}

\kifunction{dmx\_unregister\_demux()}{
  int dmx\_unregister\_demux ( dmx\_demux\_t *demux )
  }{
  This function is called to indicate that the given demux interface is no longer
  available. The caller of this function is responsible for freeing the memory of
  the demux structure, if it was dynamically allocated before calling 
  dmx\_register\_demux().
  The cleanup\_module() function of the kernel module that contains the demux 
  driver should call this function. Note that this function fails if the demux 
  is currently in use, i.e., release\_demux() has not been called for the 
  interface.
  }{
  dmx\_demux\_t* demux & Pointer to the demux structure which is to be unregistered.
  }{
  0 & The function was completed without errors.\\
  ENODEV & The specified demux is not registered in the demux directory.\\
  EBUSY  & The specified demux is currently in use.
}

\kifunction{dmx\_get\_demuxes()}{
  struct list\_head *dmx\_get\_demuxes ()
  }{
  Provides the caller with the list of registered demux interfaces, using the 
  standard list structure defined in the include file linux/list.h. 
  The include file demux.h defines the macro DMX\_DIR\_ENTRY() for converting an 
  element of the generic type struct list\_head* to the type dmx\_demux\_t*.
  The caller must not free the memory of any of the elements obtained via this
  function call.
  }{
  none
  }{
  struct list\_head * & 
  A list of demux interfaces, or NULL in the case of an empty list.
}

\clearpage 

\devsubsec{Demux API}

The demux API should be implemented for each demux in the system. It is used to
select the TS source of a demux and to manage the demux resources. When the
demux client allocates a resource via the demux API, it receives a pointer 
to the API of that resource.

Each demux receives its TS input from a DVB front-end or from memory, as 
set via the demux API. In a system with more than one front-end, the API can 
be used to select one of the DVB front-ends as a TS source for a demux, unless
this is fixed in the HW platform. The demux API only controls front-ends 
regarding their connections with demuxes; the APIs used to set the other        
front-end parameters, such as tuning, are not defined in this document.

The functions that implement the abstract interface demux should be defined
static or module private and registered to the Demux Directory for external
access. It is not necessary to implement every function in the demux\_t struct,
however (for example, a demux interface might support Section filtering, but 
not TS or PES filtering). The API client is expected to check the value of any
function pointer before calling the function: the value of NULL means ``function
not available''.

Whenever the functions of the demux API modify shared data, the possibilities
of lost update and race condition problems should be addressed, e.g. by 
protecting parts of code with mutexes. This is especially important on 
multi-processor hosts.

Note that functions called from a bottom half context must not sleep, at least
in the 2.2.x kernels. Even a simple memory allocation can result in a kernel
thread being put to sleep if swapping is needed. For example, the Linux kernel
calls the functions of a network device interface from a bottom half context.
Thus, if a demux API function is called from network device code, the function
must not sleep.

\kfunction{open()}{
  int open ( demux\_t* demux );
  }{
  This function reserves the demux for use by the caller and, if necessary, 
  initializes the demux. When the demux is no longer needed, the function close()
  should be called.
  It should be possible for multiple clients to access the demux at the same time.
  Thus, the function implementation should increment the demux usage count when 
  open() is called and decrement it when close() is called.
  }{
  demux\_t* demux & Pointer to the demux API and instance data.
  }{
  0 & The function was completed without errors.\\
  -EUSERS & Maximum usage count reached.\\
  -EINVAL & Bad parameter.
}

\kfunction{close()}{
  int close(demux\_t* demux);
  }{
  This function reserves the demux for use by the caller and, if necessary, 
  initializes the demux. When the demux is no longer needed, the function close()
  should be called.
  It should be possible for multiple clients to access the demux at the same time.
  Thus, the function implementation should increment the demux usage count when 
  open() is called and decrement it when close() is called.
  }{
  demux\_t* demux & Pointer to the demux API and instance data.
  }{
  0 & The function was completed without errors.\\
  -ENODEV & The demux was not in use.\\
  -EINVAL & Bad parameter.
}

\kfunction{write()}{
  int write(demux\_t* demux, const char* buf, size\_t count);    
  }{
  This function provides the demux driver with a memory buffer containing TS 
  packets. Instead of receiving TS packets from the DVB front-end, the demux 
  driver software will read packets from memory. Any clients of this demux 
  with active TS, PES or Section filters will receive filtered data via the Demux
  callback API (see 0). The function returns when all the data in the buffer has
  been consumed by the demux.
  Demux hardware typically cannot read TS from  memory. If this is the case,
  memory-based filtering has to be implemented entirely in software.
  }{
  demux\_t* demux  & Pointer to the demux API and instance data.\\
  const char* buf & Pointer to the TS data in kernel-space memory.\\
  size\_t length   & Length of the TS data.
  }{
  0 & The function was completed without errors.\\
  -ENOSYS & The command is not implemented.\\
  -EINVAL & Bad parameter.
}

\kifunction{allocate\_ts\_feed()}{
  int allocate\_ts\_feed(dmx\_demux\_t* demux, 
  dmx\_ts\_feed\_t** feed, dmx\_ts\_cb callback);
  }{
  Allocates a new TS feed, which is used to filter the TS packets carrying a 
  certain PID.
  The TS feed normally corresponds to a hardware PID filter on the demux chip.
  }{
  demux\_t* demux        & Pointer to the demux API and instance data.\\
  dmx\_ts\_feed\_t** feed  & Pointer to the TS feed API and instance data.\\
  dmx\_ts\_cb callback    & Pointer to the callback function for
                          passing received TS packet
  }{
  0 & The function was completed without errors.\\
  -EBUSY & No more TS feeds available.\\
  -ENOSYS & The command is not implemented.\\
  -EINVAL & Bad parameter.
}

\kifunction{release\_ts\_feed()}{
  int release\_ts\_feed(dmx\_demux\_t* demux, dmx\_ts\_feed\_t* feed);
  }{
  Releases the resources allocated with allocate\_ts\_feed(). Any filtering in progress
  on the TS feed should be stopped before calling this function.
  }{
  demux\_t* demux        & Pointer to the demux API and instance data.\\
  dmx\_ts\_feed\_t* feed  & Pointer to the TS feed API and instance data.
  }{
  0 & The function was completed without errors.\\
  -EINVAL & Bad parameter.
}

\kifunction{allocate\_section\_feed()}{
  int allocate\_section\_feed(dmx\_demux\_t* demux, dmx\_section\_feed\_t **feed,
  dmx\_section\_cb callback);
  }{
  Allocates a new section feed, i.e. a demux resource for filtering and 
  receiving sections.
  On platforms with hardware support for section filtering, a section feed is directly
  mapped to the demux HW. On other platforms, TS packets are first PID filtered in
  hardware and a hardware section filter then emulated in software.
  The caller obtains an API pointer of type dmx\_section\_feed\_t as an out parameter.
  Using this API the caller can set filtering parameters and start receiving sections.
  }{
  demux\_t *demux & Pointer to the demux API and instance data.\\
  dmx\_section\_feed\_t **feed & Pointer to the section feed API and instance data.\\
  dmx\_section\_cb callback & Pointer to the callback function for
                            passing received sections.
  }{
  0 & The function was completed without errors.\\
  -EBUSY  & No more section feeds available.\\
  -ENOSYS & The command is not implemented.\\
  -EINVAL & Bad parameter.
}


\kifunction{release\_section\_feed()}{
  int release\_section\_feed(dmx\_demux\_t* demux, dmx\_section\_feed\_t *feed);
  }{
  Releases the resources allocated with allocate\_section\_feed(), including allocated
  filters. 
  Any filtering in progress on the section feed should be stopped before calling
  this function.
  }{
  demux\_t *demux & Pointer to the demux API and instance data.\\
  dmx\_section\_feed\_t *feed & Pointer to the section feed API and instance data.
  }{
  0 & The function was completed without errors.\\
  -EINVAL & Bad parameter.
}

\kifunction{descramble\_mac\_address()}{
  int descramble\_mac\_address(dmx\_demux\_t* demux,
  \_\_u8 *buffer1, size\_t buffer1\_length,
  \_\_u8 *buffer2, size\_t buffer2\_length, \_\_u16 pid);
  }{
  This function runs a descrambling algorithm on the destination MAC address field of a
  DVB Datagram Section, replacing the original address with its un-encrypted version.
  Otherwise, the description on the function descramble\_section\_payload() applies
  also to this function.
  }{
  dmx\_demux\_t *demux & Pointer to the demux API and instance data.\\
  \_\_u8 *buffer1 & Pointer to the first byte of the section.\\
  size\_t buffer1\_length & Length of the section data, including headers and CRC, 
                          in buffer1.\\
  \_\_u8* buffer2 & Pointer to the tail of the section data, or NULL. The pointer has a
                  non-NULL value if the section wraps
                  past the end of a circular buffer.\\
  size\_t buffer2\_length & Length of the section data,
                          including headers and CRC, in buffer2.\\
  \_\_u16 pid & The PID on which the section was received. Useful for obtaining the
              descrambling key, e.g. from a DVB Common Access facility.
  }{
  0 & The function was completed without errors.\\
  -ENOSYS & No descrambling facility available.\\
  -EINVAL & Bad parameter.
}

\kifunction{descramble\_section\_payload()}{
  int descramble\_section\_payload(dmx\_demux\_t* demux,
  \_\_u8 *buffer1, size\_t buffer1\_length, \_\_u8 *buffer2, size\_t 
  buffer2\_length, \_\_u16 pid);
  }{
  This function runs a descrambling algorithm on the payload of a DVB Datagram
  Section, replacing the original payload with its un-encrypted version. 
  The function will
  be called from the demux API implementation; the API client need 
  not call this function directly.
  Section-level scrambling algorithms are currently standardized only for DVB-RCC
  (return channel over 2-directional cable TV network) systems. For all other DVB
  networks, encryption schemes are likely to be proprietary to each data broadcaster.
  Thus, it is expected that this function pointer will have the value of NULL 
  (i.e., function not available) in most demux API implementations. 
  Nevertheless, it should be possible
  to use the function pointer as a hook for dynamically adding a ``plug-in'' 
  descrambling facility to a demux driver.\\
  While this function is not needed with hardware-based section descrambling, the
  descramble\_section\_payload function pointer can be used to override the default
  hardware-based descrambling algorithm: if the function pointer has a non-NULL value,
  the corresponding function should be used instead of any descrambling hardware.
  }{
  dmx\_demux\_t *demux & Pointer to the demux API and instance data.\\
  \_\_u8 *buffer1 & Pointer to the first byte of the section.\\
  size\_t buffer1\_length & Length of the section data, including headers and CRC, in
                          buffer1.\\
  \_\_u8 *buffer2 & Pointer to the tail of the section data, or NULL. The pointer has a
                  non-NULL value if the section wraps
                  past the end of a circular buffer.\\
  size\_t buffer2\_length & Length of the section data, including headers and CRC, in
                          buffer2.\\
  \_\_u16 pid & The PID on which the section was received. Useful for obtaining the
              descrambling key, e.g. from a DVB Common Access facility.
  }{
  0 & The function was completed without errors.\\
  -ENOSYS & No descrambling facility available.\\
  -EINVAL & Bad parameter.
}

\kifunction{add\_frontend()}{
  int add\_frontend(dmx\_demux\_t *demux, dmx\_frontend\_t *frontend);
  }{
  Registers a connectivity between a demux and a front-end, i.e., indicates that the
  demux can be connected via a call to connect\_frontend() to use the given front-end
  as a TS source. The client of this function has to allocate dynamic or static 
  memory for
  the frontend structure and initialize its fields  before calling this function.
  This function is normally called during the driver initialization. 
  The caller must not free
  the memory of the frontend struct before successfully calling remove\_frontend().
  }{
  dmx\_demux\_t* demux & Pointer to the demux API and instance data.\\
  dmx\_frontend\_t* frontend & Pointer to the front-end instance data.
  }{
  0 & The function was completed without errors.\\
  -EEXIST & A front-end with the same value of the id field already registered.\\
  -EINUSE & The demux is in use.\\
  -ENOMEM & No more front-ends can be added.\\
  -EINVAL & Bad parameter.
}

\kifunction{remove\_frontend()}{
  int remove\_frontend(dmx\_demux\_t* demux, dmx\_frontend\_t* frontend);
  }{
  Indicates that the given front-end, registered by a call to add\_frontend(), can no
  longer be connected as a TS source by this demux. The function should be called
  when a front-end driver or a demux driver is removed from the system. If the front-end
  is in use, the function fails with the return value of -EBUSY.
  After successfully calling this function, the caller can free the memory of 
  the frontend struct if it was dynamically allocated before the add\_frontend() 
  operation.
  }{
  dmx\_demux\_t* demux & Pointer to the demux API and instance data.\\
  dmx\_frontend\_t* frontend & Pointer to the front-end instance data.
  }{
  0 & The function was completed without errors.\\
  -EINVAL & Bad parameter.\\
  -EBUSY & The front-end is in use, i.e. a call to
           connect\_frontend() has not been followed by
           a call to disconnect\_frontend().
}

\kifunction{get\_frontends()}{
  struct list\_head* get\_frontends(dmx\_demux\_t* demux);
  }{
  Provides the APIs of the front-ends that have been registered for this demux. Any of
  the front-ends obtained with this call can be used as a parameter for
  connect\_frontend().\\
  The include file demux.h contains the macro DMX\_FE\_ENTRY() for converting an
  element of the generic type struct list\_head* to the type dmx\_frontend\_t*.
  The caller must not free the memory of any of the elements obtained via this function
  call.
  }{
  dmx\_demux\_t* demux & Pointer to the demux API and instance data.
  }{
  dmx\_demux\_t* & A list of front-end interfaces, or NULL in the case of an empty list.
}


\kifunction{connect\_frontend()}{
  int connect\_frontend(dmx\_demux\_t* demux, dmx\_frontend\_t* frontend);
  }{
  Connects the TS output of the front-end to the input of the demux. A demux can only
  be connected to a front-end registered to the demux with the function
  add\_frontend().\\
  It may or may not be possible to connect multiple demuxes to the same front-end,
  depending on the capabilities of the HW platform. When not used, the front-end should
  be released by calling disconnect\_frontend().
  }{
  dmx\_demux\_t* demux & Pointer to the demux API and instance data.\\
  dmx\_frontend\_t* frontend & Pointer to the front-end instance data.
  }{
  0 & The function was completed without errors.\\
  -EINVAL & Bad parameter.\\
  -EBUSY & The front-end is in use.
}

\kifunction{disconnect\_frontend()}{
  int disconnect\_frontend(dmx\_demux\_t* demux);
  }{
  Disconnects the demux and a front-end previously connected by a
  connect\_frontend() call.
  }{
  dmx\_demux\_t* demux & Pointer to the demux API and instance data.
  }{
  0 & The function was completed without errors.\\
  -EINVAL & Bad parameter.
}

\clearpage

\devsubsec{Demux Callback API}

This kernel-space API comprises the callback functions that deliver filtered data to the
demux client. Unlike the other APIs, these API functions are provided by the client and
called from the demux code.

The function pointers of this abstract interface are not packed into a structure
as in the
other demux APIs, because the callback functions are registered and used
independent of each other. As an example, it is possible for the API client to provide
several callback functions for receiving TS packets and no callbacks for PES packets
or sections.

The functions that implement the callback API need not be re-entrant: when a demux
driver calls one of these functions, the driver is not allowed to call the 
function again before the original call returns. 
If a callback is triggered by a hardware interrupt, it is
recommended to use the Linux ``bottom half'' mechanism or start a tasklet instead of
making the callback function call directly from a hardware interrupt.

\kifunction{dmx\_ts\_cb()}{
  int dmx\_ts\_cb(\_\_u8* buffer1, size\_t buffer1\_length, 
  \_\_u8* buffer2, size\_t buffer2\_length,
  dmx\_ts\_feed\_t* source, dmx\_success\_t success);
  }{
  This function, provided by the client of the demux API, is called from the 
  demux code. The function is only called when filtering on this TS feed has 
  been enabled using the start\_filtering() function. \\
  Any TS packets that match the filter settings are copied to a circular buffer. 
  The filtered TS packets are delivered to the client using this callback 
  function. The size of the circular buffer is controlled by the 
  circular\_buffer\_size parameter of the set() function in the TS Feed API. It is
  expected that the buffer1 and buffer2 callback parameters point to addresses 
  within the circular buffer, but other implementations are also
  possible. Note that the called party should not try to free the memory the
  buffer1 and buffer2 parameters point to.\\
  When this function is called, the buffer1 parameter typically points to the
  start of the first undelivered TS packet within a circular buffer. The buffer2 
  buffer parameter is normally NULL, except when the received TS packets have
  crossed the last address of the circular buffer and "wrapped" to the beginning
  of the buffer. In the latter case the buffer1 parameter would contain an 
  address within the circular buffer, while the buffer2 parameter would contain 
  the first address of the circular buffer.\\
  The number of bytes delivered with this function (i.e. buffer1\_length  +
  buffer2\_length) is usually equal to the value of callback\_length parameter given
  in the set() function, with one exception: if a timeout occurs before receiving
  callback\_length bytes of TS data, any undelivered packets are immediately
  delivered to the client by calling this function. The timeout duration is 
  controlled by the set() function in the TS Feed API.\\
  If a TS packet is received with errors that could not be fixed by the TS-level
  forward error correction (FEC), the Transport\_error\_indicator flag of the TS 
  packet header should be set. The TS packet should not be discarded, as the 
  error can possibly be corrected by a higher layer protocol.
  If the called party is slow in processing the callback, it is possible that 
  the circular buffer eventually fills up. If this happens, the demux driver 
  should discard any TS packets received while the buffer is full. The error 
  should be indicated to the client on the next callback by setting the success
  parameter to the value of DMX\_OVERRUN\_ERROR.\\
  The type of data returned to the callback can be selected by the 
  new function int (*set\_type) (struct dmx\_ts\_feed\_s* feed, int type, 
  dmx\_ts\_pes\_t pes\_type) which is part of the dmx\_ts\_feed\_s struct
  (also cf. to the include file ost/demux.h)
  The type parameter decides if the raw TS packet (TS\_PACKET) or just the
  payload (TS\_PACKET|TS\_PAYLOAD\_ONLY) should be returned.
  If additionally the TS\_DECODER bit is set the stream will also be sent 
  to the hardware MPEG decoder. In this case, the second flag decides 
  as what kind of data the stream should be interpreted.
  The possible choices are one of DMX\_TS\_PES\_AUDIO, DMX\_TS\_PES\_VIDEO,
  DMX\_TS\_PES\_TELETEXT, DMX\_TS\_PES\_SUBTITLE, DMX\_TS\_PES\_PCR, or
  DMX\_TS\_PES\_OTHER.
  }{
  \_\_u8* buffer1 & Pointer to the start of the filtered TS packets.\\
  size\_t buffer1\_length & Length of the TS data in buffer1.\\
  \_\_u8* buffer2         & Pointer to the tail of the filtered TS packets, or NULL.\\
  size\_t buffer2\_length & Length of the TS data in buffer2.\\
  dmx\_ts\_feed\_t* source & Indicates which TS feed is the source of the callback.\\
  dmx\_success\_t success & Indicates if there was an error in TS reception.
  }{
  0 & Continue filtering.\\
  -1& Stop filtering - has the same effect as a call
      to stop\_filtering() on the TS Feed API.
}

\kifunction{dmx\_section\_cb()}{
  int dmx\_section\_cb(\_\_u8* buffer1, size\_t buffer1\_length, \_\_u8* buffer2,
  size\_t buffer2\_length, dmx\_section\_filter\_t* source,
  dmx\_success\_t success);
  }{
  This function, provided by the client of the demux API, is called from the demux code.
  The function is only called when filtering of sections has been enabled using the
  function start\_filtering() of the section feed API.
  When the demux driver has received a complete section that matches at least one
  section filter, the client is notified via this callback function. Normally this function is
  called for each received section; however, it is also possible to deliver multiple sections
  with one callback, for example when the system load is high.
  If an error occurs while receiving a section, this function should be called with the
  corresponding error type set in the success field, whether or not there is data to
  deliver.
  The Section Feed implementation should maintain a circular buffer for received sections.
  However, this is not necessary if the Section Feed API is implemented as a client of
  the TS Feed API, because the TS Feed implementation then buffers the
  received data.
  The size of the circular buffer can be configured using the set() function in the
  Section Feed API. If there is no room in the circular buffer when a new section is
  received, the section must be discarded. If this happens, the value of the success
  parameter should be DMX\_OVERRUN\_ERROR on the next callback.
  }{
  \_\_u8* buffer1  & Pointer to the start of the filtered section, e.g.
                   within the circular buffer of the demux driver.\\
  size\_t buffer1\_length & Length of the filtered section data in buffer1,
                          including headers and CRC.\\
  \_\_u8* buffer2         & Pointer to the tail of the filtered section data, or
                          NULL. Useful to handle the wrapping of a circular
                          buffer.\\
  size\_t buffer2\_length & Length of the filtered section data in buffer2,
                          including headers and CRC.\\
  dmx\_section\_filter\_t* filter & Indicates the filter that triggered the callback.\\
  dmx\_success\_t success & Indicates if there was an error in section reception.
  }{
  0 & Continue filtering.\\
  -1& Stop filtering - has the same effect as a call
      to stop\_filtering() on the Section Feed API.
}

\clearpage

\devsubsec{TS Feed API}

A TS feed is typically mapped to a hardware PID filter on the demux chip. Using this
API, the client can set the filtering properties to start/stop filtering TS packets on a
particular TS feed. The API is defined as an abstract interface of the type
dmx\_ts\_feed\_t.

The functions that implement the interface should be defined static or module
private. The client can get the handle of a TS feed API by calling the function
allocate\_ts\_feed() in the demux API.

\kifunction{set()}{
  int set ( dmx\_ts\_feed\_t* feed, \_\_u16 pid, size\_t callback\_length,
  size\_t circular\_buffer\_size, int descramble, struct timespec timeout);
  }{
  This function sets the parameters of a TS feed. 
  Any filtering in progress on the TS feed
  must be stopped before calling this function.
  }{
  dmx\_ts\_feed\_t* feed & Pointer to the TS feed API and instance data.\\
  \_\_u16 pid & PID value to filter. Only the TS packets carrying the specified PID will
              be passed to the API client.\\
  size\_t callback\_length & Number of bytes to deliver with each
                           call to the dmx\_ts\_cb() callback
                           function. The value of this
                           parameter should be a multiple of 188.\\
  size\_t circular\_buffer\_size & Size of the circular buffer for the filtered TS packets.\\
  int descramble & If non-zero, descramble the filtered TS packets.\\
  struct timespec timeout & Maximum time to wait before
                            delivering received TS packets to the client.
  }{
  0 & The function was completed without errors.\\
  -ENOMEM & Not enough memory for the requested buffer size.\\
  -ENOSYS & No descrambling facility available for TS.\\
  -EINVAL & Bad parameter.
}


\kifunction{start\_filtering()}{
  int start\_filtering(dmx\_ts\_feed\_t* feed);
  }{
  Starts filtering TS packets on this TS feed, according to its settings. 
  The PID value to filter can be set by the API client. 
  All matching TS packets are delivered asynchronously to the client, 
  using the callback function registered with allocate\_ts\_feed().
  }{
  dmx\_ts\_feed\_t* feed & Pointer to the TS feed API and instance data.
  }{
  0 & The function was completed without errors.\\
  -EINVAL & Bad parameter.
}

\kifunction{stop\_filtering()}{
  int stop\_filtering(dmx\_ts\_feed\_t* feed);
  }{
  Stops filtering TS packets on this TS feed.
  }{
  dmx\_ts\_feed\_t* feed & Pointer to the TS feed API and instance data.
  }{
  0 & The function was completed without errors.\\
  -EINVAL & Bad parameter.
}

\clearpage

\devsubsec{Section Feed API}

A section feed is a resource consisting of a PID filter and a set of section filters.
Using this API, the client can set the properties of a section feed and to 
start/stop filtering.
The API is defined as an abstract interface of the type dmx\_section\_feed\_t.
The functions that implement the interface should be defined static or module
private. The client can get the handle of a section feed API by calling the function
allocate\_section\_feed() in the demux API.

On demux platforms that provide section filtering in hardware, the Section Feed API
implementation provides a software wrapper for the demux hardware. Other platforms
may support only PID filtering in hardware, requiring that TS packets are converted to
sections in software. In the latter case the Section Feed API implementation can be a
client of the TS Feed API.


\kifunction{set()}{
  int set(dmx\_section\_feed\_t* feed, \_\_u16 pid, size\_t circular\_buffer\_size, 
  int descramble, int check\_crc);
  }{
  This function sets the parameters of a section feed. Any filtering in progress on the
  section feed must be stopped before calling this function.
  If descrambling is enabled, the payload\_scrambling\_control and
  address\_scrambling\_control fields of received DVB datagram sections should be
  observed. If either one is non-zero, the section should be descrambled either in
  hardware or using the functions descramble\_mac\_address() and
  descramble\_section\_payload() of the demux API. Note that according to the
  MPEG-2 Systems specification, only the payloads of private sections can be
  scrambled while the rest of the section data must be sent in the clear.
  }{
  dmx\_section\_feed\_t* feed & Pointer to the section feed API and instance data.\\
  \_\_u16 pid   & PID value to filter; only the TS packets
                carrying the specified PID will be accepted.\\
  size\_t circular\_buffer\_size & Size of the circular buffer for filtered sections.\\
  int descramble      & If non-zero, descramble any sections that are scrambled.\\
  int check\_crc       & If non-zero, check  the CRC values of filtered sections. 
  }{
  0 & The function was completed without errors.\\
  -ENOMEM & Not enough memory for the requested buffer size.\\
  -ENOSYS & No descrambling facility available for sections.\\
  -EINVAL & Bad parameters.
}

\kifunction{allocate\_filter()}{
  int allocate\_filter(dmx\_section\_feed\_t* feed, dmx\_section\_filter\_t** filter);
  }{
  This function is used to allocate a section filter on the demux. 
  It should only be called when no filtering is in progress on this section feed. 
  If a filter cannot be allocated, the function fails with -ENOSPC. 
  See in section \ref{sectionfilter} for the format of the section filter. \\
  The bitfields filter\_mask and filter\_value should only be modified when no
  filtering is in progress on this section feed. filter\_mask controls which bits of
  filter\_value are compared with the section headers/payload. On a binary value of 1
  in filter\_mask, the corresponding bits are compared. The filter only accepts sections
  that are equal to filter\_value in all the tested bit positions. Any changes to the
  values of filter\_mask and filter\_value are guaranteed to take effect only when
  the start\_filtering()  function is called next time. The parent pointer in the struct
  is initialized by the API implementation to the value of the feed parameter. The priv
  pointer is not used by the API implementation, and can thus be freely utilized by the
  caller of this function. Any data pointed to by the priv pointer is available to the
  recipient of the dmx\_section\_cb() function call.\\
  While the maximum section filter length (DMX\_MAX\_FILTER\_SIZE) 
  is currently set at 16 bytes, hardware filters of that size are not 
  available on all platforms. Therefore, section filtering will often 
  take place first in hardware, followed by filtering in software for the
  header bytes that were not covered by a hardware filter. 
  The filter\_mask field can be checked to determine how many bytes of 
  the section filter are actually used, and if the
  hardware filter will suffice. Additionally, software-only section filters
  can optionally be
  allocated to clients when all hardware section filters are in use.
  Note that on most demux hardware it is not possible to filter on the
  section\_length field
  of the section header -- thus this field is ignored, even though it is included in
  filter\_value and filter\_mask fields.
  }{
  dmx\_section\_feed\_t* feed & Pointer to the section feed API and instance data.\\
  dmx\_section\_filter\_t** filter & Pointer to the allocated filter.
  }{
  0 & The function was completed without errors.\\
  -ENOSPC & No filters of given type and length available.\\
  -EINVAL & Bad parameters.
}

\kifunction{release\_filter()}{
  int release\_filter ( dmx\_section\_feed\_t* feed, dmx\_section\_filter\_t* filter);
  }{
  This function releases all the resources of a previously allocated section filter. 
  The function should not be called while filtering is in progress on this section feed.
  After calling this function, the caller should not try to dereference the 
  filter pointer.
  }{
  dmx\_section\_feed\_t* feed & Pointer to the section feed API and instance data.\\
  dmx\_section\_filter\_t* filter & I/O Pointer to the instance data of a section filter.
  }{
  0 & The function was completed without errors.\\
  -ENODEV & No such filter allocated.\\
  -EINVAL & Bad parameter.
}

\kifunction{start\_filtering()}{
  int start\_filtering ( dmx\_section\_feed\_t* feed );
  }{
  Starts filtering sections on this section feed, according to its settings. 
  Sections are first filtered based on their PID and then matched with the 
  section filters allocated for this feed. 
  If the section matches the PID filter and at least one section filter, it is delivered
  to the API client. The section is delivered asynchronously using the callback function
  registered with allocate\_section\_feed().
  }{
  dmx\_section\_feed\_t* feed  & Pointer to the section feed API and instance data.\\
  }{
  0 & The function was completed without errors.\\
  -EINVAL & Bad parameter.
}

\kifunction{stop\_filtering()}{
  int stop\_filtering ( dmx\_section\_feed\_t* feed );
  }{
  Stops filtering sections on this section feed. Note that any changes to the 
  filtering parameters (filter\_value, filter\_mask, etc.) should only be made 
  when filtering is stopped.
  }{
  dmx\_section\_feed\_t* feed & Pointer to the section feed API and instance data.
  }{
  0 & The function was completed without errors.\\
  -EINVAL & Bad parameter.
}



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