dddvb/docs/bbframes

To allow the transport of DVB-S2 baseband frames (BBFrame) across existing hard- and software
interfaces, we have added the ability to embed the BBFrame data into
an MPEG2 transport stream.

This feature is available on supported cards as firmware update and
is currently considered experimental.

Supported hardware:

cineS2 V7A                (>=1.7 FW)
OctopusCI S2 Pro Advanced (>=1.7 FW)
Duoflex S2 v4 Advanced    (TBA)
MaxSX8                    (NOT the MAXS8!)

The following cards are based on the broadcast version of the
DVB-S2 demodulator. The BBFrame output is working but
not documented. We therefore can not guarantee the
feature will work under all conditions.

cineS2 V7              (>=1.7 FW)
OctopusCI S2 Pro       (>=1.7 FW)
Duoflex S2 v4          (TBA)


Current FPGA images (including FW 1.7 for the above mentioned cards)
can be found here:

http://download.digital-devices.de/download/firmware/html/firmwareupdate.html



Packet format:

The BBFrames are packetized into MPEG2 private sections (0x80), one section per transport stream
packet. The PID is fixed at 0x010E.


Header packet of frame:

0x47 0x41 0x0E 0x1X 0x00 0x80 0x00 L 0xB8 BBHeader (169 * Data)

L: Section Length, always 180 (0xB4)
BBHeader: 10 Bytes BBFrame header (see DVB-S2, EN-302307)
Data: 169 Bytes of BBFrame payload


Payload packets:

0x47 0x41 0x0E 0x1X 0x00 0x80 0x00 L N (179 * Data)

L: Section Length, always 180 (0xB4)
N: Packet counter, starting with 0x01 after header packet
Data: 179 Bytes of BBFrame payload


Last packet:
0x47 0x41 0x0E 0x1X 0x00 0x80 0x00 L N ((L-1) * Data)  ((180 – L) * 0xFF)

L: Section Length, remaining Data – 1, (0x01 .. 0xB4)
N: Packet counter
Data: L-1 Bytes of BBFrame payload



Automatic detection of input format:

The bridge firmware allows automatic detection of the incoming data.
To receive regular transport streams in this formats it is still required to setup
the DVB-S2 demodulator to output BBFrames instead of regular TS Packets.
When enabled the embedding mode is automatically turned on or off depending on incoming data
from the DVB-S2/S2X frontend. The decision depends currently only on the first byte of a packet.
If it is 0x47 it switches to transport stream mode else it switches to embedding mode.

Note that 0x47 can currently not occur in the first byte of a BBFrame header if all reserved
values of DVB-S2 and -S2X are observed.




API:

Currently DTV_STREAM_ID is misused.
Set it to 0x80000000 to enable frame mode in the demod.



Because there were some questions why we use this data format,
here are some examples for why using this format this makes handling BBFrames easier:

- The start of a frame is easily found  because a new set of sections is
  started. 
  
- Existing software layers like the Linux kernel DVB demuxer can be used unchanged.

- Existing hardware like the OctopusNet SAT>IP server which can only handle TS packets can
  stream BBFrames via SAT>IP with this method.

- There is at least one demodulator (e.g. on the MaxSX8) which supports this format in hardware.