SAA7205 Philips Semiconductors, SAA7205 Datasheet - Page 41

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

Philips Semiconductors
Table 8 Definition of interrupt mechanism
Table 9 Unit contents
The microcontroller interface module contains a short filter
module, a long module and a subtitling module. These
filter modules allow the microcontroller to retrieve several
sorts of data from the incoming transport stream.
7.14.1
The short filter module is capable of accessing, for
instance, program specific or service information,
transported in sections, with a length of up to and including
1997 Jan 21
BIT NUMBER
UNIT NUMBER
MPEG-2 systems demultiplexer
REGISTER
10
12
13
11
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
S
HORT FILTER MODULE
a new PCR arrived, STC_B preset
a new video PTS arrived
a new video DTS arrived
video emulated PTS matched STC
a new PCR arrived, STC_A preset
a new audio PTS arrived
audio emulated PTS matched STC
audio output processing was restarted
the difference: STC - emulated PTS
was recalculated at the audio FIFO
output
the parser lost synchronization
subtitling FIFO level at threshold
TXT FIFO level at threshold
one of the 12 short detection units
detected data
one of the 4 long detection units
detected data
interrupt request handling control
parser input control
error handling, error count
data filtering control
PCR and timing regeneration control
video filtering and interfacing control
audio filtering and interfacing control
GP and HS Data filtering control
TXT filtering control
MEANING OF INTERRUPT
UNIT CONTENTS
41
1 kBytes. The configuration of the short filter module is
shown in Fig. 28.
The filter consists of 12 section detectors. Each section
detector selects and retrieves section data on the basis of:
The section data detected by a certain section detector is
always stored in the associated 1 kByte section buffer.
As soon as an entire section of data is stored, an interrupt
(interrupt: ‘flt0_B_irpt’, address 0x0000, see Table 13) is
generated. The 12 section detectors can be separately
enabled (disabled), to avoid unnecessary interrupts.
The ‘filter fired’ registers enable the microcontroller to track
which section detector loaded its buffer (bits: ‘flt
[B to 0]_frd’, address 0x0304, see Table 13). Each of the
section detectors checks incoming section data for errors,
by means of the CRC_32 mechanism specified in MPEG2
systems. If an error is detected, an error status flag is set
(bit: ‘err_stat’, see Table 13). The error flag can therefore
be accessed by the microcontroller.
If the microcontroller decides to read data from one of the
buffers (see Table 13, address range as indicated in
Table 10) it can determine when to stop reading in two
ways. It can periodically poll the ‘flt [B to 0]_stat’ bits in the
interrupt status register (address 0x0003, see Table 13).
These bits go LOW as soon as the last valid section data
word is read from the buffer in question.
Another possibility is for the microcontroller to read the
‘high_address’ word (‘hadr [B to 0]’, see Table 13). This
word is proportional to the number of valid section words
(1 word equals 2 bytes) that was written into the buffer.
Actually #words equal ‘high_address’ + 1. This number
equals the number of read cycles that has to be performed
to retrieve all valid data from the section buffer.
If the buffer contents have to be removed without being
read, the microcontroller can write a logic 1 to one of the
‘rst_bf [B to 0]’ bits (address 0x0315, see Table 13), thus
releasing the buffer. Another possibility is to perform one
write address operation to (0x.... - hadr [B to 0] + 1).
The internal auto increment address counter is thus set to
the last byte in the buffer. The filters are reactivated after
having been idle during buffer emptying.
PID
Table_id
4 maskable bytes (32 bits) in the section payload
(see Fig 28).
Preliminary specification
SAA7205H