Arch
32 Wed May 28 17:36:23 1997
Draft 1/21/97
2-32
Architecture
PRE.4 for Rev. D
Copyright 1997 by LSI Logic Corporation. All rights reserved.
2.3.2.10 Adaptation Field Processing
When a packet containing an adaptation eld arrives (AF = 102, or AF =
112), the PID Post-processor performs several operations on some elds
in the adaptation eld. If the AF attribute bit is set to one, the AF is
posted to the MMU. The following elds and ags are processed:
Adaptation Field Length (AFL)
This 8-bit eld species the length of the adaptation eld immediately
following the AFL eld. The AFL is used to calculate the value in the
length byte when the data is posted to the MMU.
Discontinuity Indicator (DI)
This 1-bit eld indicates a discontinuity. When DI is detected, the CC
in this packet is loaded and used as a reference for the next packets.
Any CC discontinuity is ignored. If the EI bit for this PID in the ACRF
register is set to one, an interrupt of discontinuity is generated.
Random Access Indicator (RAI)
This 1-bit eld indicates that the next PES packet with the same PID
contains a random access point. If it is PES video, it indicates that
the payload of the next packet with the same PID carries a video
sequence start header. If it is audio PES, it indicates that the payload
of the next packet of the same PID carries an audio start frame
header.
Splice Point Indicator (SPI)
This 1-bit eld species that this adaptation eld includes a splicing
point counter. The value of this counter is extracted and posted to
the Splice Countdown Register (0xFFFF5).
Splice Counter
The Splice Counter is a eld extracted from the adaptation eld when
the SPI is set to 1 (see
Figure 2.29). This is for audio and video PID
transport packets (PID Indexes 30 and 31).
When the splice count is extracted, the L64007 decrements the value
by 1 for every transport packet with the same PID. The user must
poll the count down value to nd the splice point time.