2/24/2008 9T6WP
Preliminary Hardware Data Module BCM7405
06/29/07 Functional Description
Broadcom Corporation
Document 7405-1HDM00-R Data Transport Processor Page 1-23
transport field tables which can then be used during playback to perform trick modes. RASP, as defined by NDS, can be
supported using TPIT. Up to five record channels can be configured for the TPIT function.
A local timestamp is generated at the input buffer via an internal counter using a 27-MHz clock selectable from any of the
three available locked timebases, or the free-running system clock. The local timestamp can be prepended as a 32-bit field
to each recorded transport packet. The format of the 32-bit timestamp filed is programmable. In one mode, this field contains
a 28-bit local timestamp plus a 4-bit parity which can be used during playback to transmit the packets at a rate equivalent to
when they were recorded and can be used for PCR correction in the Remux modules. In another mode, the upper two bits
of the 32-bit timestamp field are user programmable with the remaining bits being the timestamp.
Record Channel’s Index Table Generation
Index table generation is a function that is supported in the record channel. Although this function handles more than just
start code table entries, it will be referred to as the SCD (start code detector) in this document.
The SCD records the positions of PES packet header stream_id's and elementary stream start codes within a recorded
transport stream for a given PID. There are two transport modes of operation: MPEG and DIRECTV. The data structure for
data stored in the memory buffer is a start code index table that is detailed in the Record Index Table Definition section.
Within each transport mode (MPEG and DIRECTV), there are four index table modes supported. All modes utilize a 6-word
index entry. Four index entry types are supported: Start Code (SC), Presentation Time Stamp (PTS), Transport Field (TF),
and Seamless Pause (SP). The following describes the four entry types:
1 The SC index entry provides offsets to start-code locations within the associated record buffer.
2 The PTS index entry provides PTS values extracted from the recorded stream.
3 The TPIT transport field parser stores transport field index entries. For the on-change conditions, an initial entry is made
for detection of the first PID. For example, if the first packet for a PID with the transport_scrambling_control_change_en
bit set has a scrambling control of 10, an index table entry is stored for the transport_scrambling_control_change
condition with the transport_scrambling_control_change bit set and the actual value of the scrambling_control of 10 is
stored in the scram_control field.
4 The seamless pause feature is intended for use with playback. It allows live viewing of a program with the capability of
pausing the program. The program is initially viewed without going through the record/playback path. This eliminates
channel change latency incurred when going through this path. When the user wishes to pause the program, a record
channel must be enabled with the appropriate PID channels selected for record. Then REC_PAUSE_EN is asserted.
This assertion prevents the selected PID channel data from being sent to the audio/video decoders. The user sees this
as a pause. Once REC_PAUSE_EN is set, the next packet that is recorded has a seamless pause entry made in the
record index table (if the index table is enabled). When the user wishes to resume the program, the stream now comes
from a playback channel instead of the live channel. The index table entry made for seamless pause is used to determine
where to start the playback.
SCD Elementary Stream Start Code Detection
The SCD module parses the system transport and PES layer to find elementary stream (ES) start codes. First, the transport
layer is parsed to determine what is transport payload. In PES mode, the PES layer is parsed to find the desired ES (all data
besides the PES header).
The data that is determined to be the desired ES is fed to a start code detector that looks for the pattern 000001XX where
XX is a start code.
Transport packet synchronization and filtering is done using a packet sync signal, a host CPU programmed PID and
transport mode specific criteria. The payload data is found in the following manner:
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