SAA7205 Philips Semiconductors, SAA7205 Datasheet - Page 16

• Manufacturer Part Number: SAA7205
• Description: MPEG-2 systems demultiplexer
• Manufacturer: Philips Semiconductors

Philips Semiconductors
7.3
The error handling module responds to four situations in
which errors are present in the incoming stream:
In the first two cases, the transport_error_indicator bit in
the transport packet header is set. In all cases error
handling depends on the data stream the packet belongs
to, as indicated in Table 3. Most of the functions in this
table are executed in the data filters, not in the error
handling module. Error handling is therefore implemented
as a distributed function.
Table 3 Error handling algorithms
1997 Jan 21
DATA STREAM
Video
Audio
TXT
Subtitling
High speed
data
Section data
An erroneous packet is signalled to the demultiplexer,
by means of the PKTBAD/PKTBAD input signal.
The FEC decoder drives this signal LOW (or HIGH)
should it discovers that the number of errors in a packet
exceeds its correction capability. The polarity of the
PKTBAD/PKTBAD input signal is programmable
(bit Bad_pol, address 0x0100; see Table 13).
The transport_error_indicator bit in the transport packet
header is set (equals logic 1), indicating that an error
occurred prior to, or during transmission
A continuity counter discontinuity is detected
The parser detects a syntax error in a packet, or is out
of sync.
MPEG-2 systems demultiplexer
Error handling
third party decoder erroneous transport packets are discarded, no error flag is set, but a
SAA7201
OPTION
sequence_error_code (0x000001B4) is inserted, whenever a
continuity_counter discontinuity is discovered
handling is altogether done in the SAA7201 source decoder
discard erroneous packets
discard erroneous packets
PES packet data are passed to the microcontroller. The error handling
decision is left to the microcontroller.
programmable error handling (see Section “High speed data interfacing”)
CRC calculation is performed in the filters. If an error is detected, an error flag
(bit err_stat, address 0x0305 to 0x0314, see Table 13) is set. The error
handling decision is left to the microcontroller.
16
If the parser detects a syntax error or is out of sync, the
error handling module discards all incoming data, and an
interrupt is set (bit prs_sync_lost, address 0x0000,
see Table 13).
The error handling module keeps track of an average error
count. The module counts every occurrence of both
PKTBAD = 0 (or PKTBAD = 1) and
“transport_error_indicator = 1. The 16-bit error count value
can be read by the microcontroller, which can also reset
the counter every once in a while by writing all zeroes
(00..00) to the register (word cnt15 to cnt0], address
0x0200; see Table 13). The microcontroller can thus
determine an average packet error rate.
ERROR HANDLING
Preliminary specification
SAA7205H