# Kernel Demux API

The kernel demux API defines a driver-internal interface for registering low-level, hardware specific driver to a hardware independent demux layer. It is only of interest for DVB device driver writers. The header file for this API is named demux.h and located in drivers/media/dvb-core.

Maintainer note: This section must be reviewed. It is probably out of date.

# Kernel Demux Data Types

## dmx_success_t

     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;

## TS filter types

     /⋆--------------------------------------------------------------------------⋆/
     /⋆ 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) ⋆/

## dmx_ts_pes_t

The structure

     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;

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.

     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;

     /⋆--------------------------------------------------------------------------⋆/
     /⋆ 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;

     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;

     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;

     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

## demux_demux_t

     /⋆
      ⋆ 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;

## Demux directory

     /⋆
      ⋆ 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);

# 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.

## dmx_register_demux()

DESCRIPTION

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(),

SYNOPSIS

int dmx_register_demux ( dmx_demux_t ⋆demux )

PARAMETERS

dmx_demux_t* demux | Pointer to the demux structure.

RETURNS

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.

## dmx_unregister_demux()

DESCRIPTION

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.

SYNOPSIS

int dmx_unregister_demux ( dmx_demux_t ⋆demux )

PARAMETERS

dmx_demux_t* demux | Pointer to the demux structure which is to be unregistered.

RETURNS

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.

## dmx_get_demuxes()

DESCRIPTION

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.

SYNOPSIS

struct list_head ⋆dmx_get_demuxes ()

PARAMETERS

none

RETURNS

struct list_head * | A list of demux interfaces, or NULL in the case of an empty list.

# 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.

## open()

DESCRIPTION

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.

SYNOPSIS

int open ( demux_t⋆ demux );

PARAMETERS

demux_t* demux | Pointer to the demux API and instance data.

RETURNS

0 | The function was completed without errors.
-EUSERS | Maximum usage count reached.
-EINVAL | Bad parameter.

## close()

DESCRIPTION

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.

SYNOPSIS

int close(demux_t⋆ demux);

PARAMETERS

demux_t* demux | Pointer to the demux API and instance data.

RETURNS

0 | The function was completed without errors.
-ENODEV | The demux was not in use.
-EINVAL | Bad parameter.

## write()

DESCRIPTION

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.

SYNOPSIS

int write(demux_t⋆ demux, const char⋆ buf, size_t count);

PARAMETERS

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.

RETURNS

0 | The function was completed without errors.
-ENOSYS | The command is not implemented.
-EINVAL | Bad parameter.

## allocate_ts_feed()

DESCRIPTION

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.

SYNOPSIS

int allocate_ts_feed(dmx_demux_t⋆ demux, dmx_ts_feed_t⋆⋆ feed, dmx_ts_cb callback);

PARAMETERS

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

RETURNS

0 | The function was completed without errors.
-EBUSY | No more TS feeds available.
-ENOSYS | The command is not implemented.
-EINVAL | Bad parameter.

## release_ts_feed()

DESCRIPTION

Releases the resources allocated with allocate_ts_feed(). Any filtering in progress on the TS feed should be stopped before calling this function.

SYNOPSIS

int release_ts_feed(dmx_demux_t⋆ demux, dmx_ts_feed_t⋆ feed);

PARAMETERS

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.

RETURNS

0 | The function was completed without errors.
-EINVAL | Bad parameter.

## allocate_section_feed()

DESCRIPTION

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.

SYNOPSIS

int allocate_section_feed(dmx_demux_t⋆ demux, dmx_section_feed_t ⋆⋆feed, dmx_section_cb callback);

PARAMETERS

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.

RETURNS

0 | The function was completed without errors.
-EBUSY | No more section feeds available.
-ENOSYS | The command is not implemented.
-EINVAL | Bad parameter.

## release_section_feed()

DESCRIPTION

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.

SYNOPSIS

int release_section_feed(dmx_demux_t⋆ demux, dmx_section_feed_t ⋆feed);

PARAMETERS

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.

RETURNS

0 | The function was completed without errors.
-EINVAL | Bad parameter.

## descramble_mac_address()

DESCRIPTION

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.

SYNOPSIS

int descramble_mac_address(dmx_demux_t⋆ demux, __u8 ⋆buffer1, size_t buffer1_length, __u8 ⋆buffer2, size_t buffer2_length, __u16 pid);

PARAMETERS

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.

RETURNS

0 | The function was completed without errors.
-ENOSYS | No descrambling facility available.
-EINVAL | Bad parameter.

## descramble_section_payload()

DESCRIPTION

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.

SYNOPSIS

int descramble_section_payload(dmx_demux_t⋆ demux, __u8 ⋆buffer1, size_t buffer1_length, __u8 ⋆buffer2, size_t buffer2_length, __u16 pid);

PARAMETERS

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.

RETURNS

0 | The function was completed without errors.
-ENOSYS | No descrambling facility available.
-EINVAL | Bad parameter.

## add_frontend()

DESCRIPTION

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().

SYNOPSIS

int add_frontend(dmx_demux_t ⋆demux, dmx_frontend_t ⋆frontend);

PARAMETERS

dmx_demux_t* demux | Pointer to the demux API and instance data.
dmx_frontend_t* frontend | Pointer to the front-end instance data.

RETURNS

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.

## remove_frontend()

DESCRIPTION

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.

SYNOPSIS

int remove_frontend(dmx_demux_t⋆ demux, dmx_frontend_t⋆ frontend);

PARAMETERS

dmx_demux_t* demux | Pointer to the demux API and instance data.
dmx_frontend_t* frontend | Pointer to the front-end instance data.

RETURNS

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().

## get_frontends()

DESCRIPTION

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.

SYNOPSIS

struct list_head⋆ get_frontends(dmx_demux_t⋆ demux);

PARAMETERS

dmx_demux_t* demux | Pointer to the demux API and instance data.

RETURNS

dmx_demux_t* | A list of front-end interfaces, or NULL in the case of an empty list.

## connect_frontend()

DESCRIPTION

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().

SYNOPSIS

int connect_frontend(dmx_demux_t⋆ demux, dmx_frontend_t⋆ frontend);

PARAMETERS

dmx_demux_t* demux | Pointer to the demux API and instance data.
dmx_frontend_t* frontend | Pointer to the front-end instance data.

RETURNS

0 | The function was completed without errors.
-EINVAL | Bad parameter.
-EBUSY | The front-end is in use.

## disconnect_frontend()

DESCRIPTION

Disconnects the demux and a front-end previously connected by a connect_frontend() call.

SYNOPSIS

int disconnect_frontend(dmx_demux_t⋆ demux);

PARAMETERS

dmx_demux_t* demux | Pointer to the demux API and instance data.

RETURNS

0 | The function was completed without errors.
-EINVAL | Bad parameter.

# 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.

## dmx_ts_cb()

DESCRIPTION

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.

SYNOPSIS

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);

PARAMETERS

__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.

RETURNS

0 | Continue filtering.
-1 | Stop filtering - has the same effect as a call to stop_filtering() on the TS Feed API.

## dmx_section_cb()

DESCRIPTION

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.

SYNOPSIS

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);

PARAMETERS

__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.

RETURNS

0 | Continue filtering.
-1 | Stop filtering - has the same effect as a call to stop_filtering() on the Section Feed API.

# 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.

## set()

DESCRIPTION

This function sets the parameters of a TS feed. Any filtering in progress on the TS feed must be stopped before calling this function.

SYNOPSIS

int set ( dmx_ts_feed_t⋆ feed, __u16 pid, size_t callback_length, size_t circular_buffer_size, int descramble, struct timespec timeout);

PARAMETERS

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.

RETURNS

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.

## start_filtering()

DESCRIPTION

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().

SYNOPSIS

int start_filtering(dmx_ts_feed_t⋆ feed);

PARAMETERS

dmx_ts_feed_t* feed | Pointer to the TS feed API and instance data.

RETURNS

0 | The function was completed without errors.
-EINVAL | Bad parameter.

## stop_filtering()

DESCRIPTION

Stops filtering TS packets on this TS feed.

SYNOPSIS

int stop_filtering(dmx_ts_feed_t⋆ feed);

PARAMETERS

dmx_ts_feed_t* feed | Pointer to the TS feed API and instance data.

RETURNS

0 | The function was completed without errors.
-EINVAL | Bad parameter.

# 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.

# set()

DESCRIPTION

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.

SYNOPSIS

int set(dmx_section_feed_t⋆ feed, __u16 pid, size_t circular_buffer_size, int descramble, int check_crc);

PARAMETERS

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.

RETURNS

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.

# allocate_filter()

DESCRIPTION

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 ?? 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.

SYNOPSIS

int allocate_filter(dmx_section_feed_t⋆ feed, dmx_section_filter_t⋆⋆ filter);

PARAMETERS

dmx_section_feed_t* feed | Pointer to the section feed API and instance data.
dmx_section_filter_t** filter | Pointer to the allocated filter.

RETURNS

0 | The function was completed without errors.
-ENOSPC | No filters of given type and length available.
-EINVAL | Bad parameters.

# release_filter()

DESCRIPTION

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.

SYNOPSIS

int release_filter ( dmx_section_feed_t⋆ feed, dmx_section_filter_t⋆ filter);

PARAMETERS

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.

RETURNS

0 | The function was completed without errors.
-ENODEV | No such filter allocated.
-EINVAL | Bad parameter.

# start_filtering()

DESCRIPTION

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().

SYNOPSIS

int start_filtering ( dmx_section_feed_t⋆ feed );

PARAMETERS

dmx_section_feed_t* feed | Pointer to the section feed API and instance data.

RETURNS

0 | The function was completed without errors.
-EINVAL | Bad parameter.

# stop_filtering()

DESCRIPTION

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.

SYNOPSIS

int stop_filtering ( dmx_section_feed_t⋆ feed );

PARAMETERS

dmx_section_feed_t* feed | Pointer to the section feed API and instance data.

RETURNS

0 | The function was completed without errors.
-EINVAL | Bad parameter.