
4-12
Video Data Flow
Final Rev F
Copyright 1996 by LSI Logic Corporation. All rights reserved.
The User Data FIFO is 128 bytes deep for Revision E, and 96 bytes for
Revision D and earlier. Note that the decoder parses user data at one-
byte/cycle, so the FIFO can be lled very quickly when large amounts of
user data are in the channel.
Overow and Empty condition ags are available in the Group 2 Status
1 Register which can be read through the system microcontroller port.
User Data FIFO Status bits. The FIFO overow ag can only be reset
either upon device reset or under host control. Typically, the system con-
troller should check for FIFO Empty before it begins to read the data and
check for FIFO Ready after it has read the data. The specic condition
of FIFO Underow is not specially agged. If FIFO Underow is possible
in a given system, then the system controller should poll the FIFO Empty
ag and prevent underow from happening.
When the decoder writes data to the User Data FIFO, it tags the data
with the layer of the MPEG grammar from which it originated. Because
there are three layers from which user data can originate, the tag is two
bits long. The tag may be optionally read
before reading the user data
through the User Data register in the system controller interface. Refer
4.3.3
Auxiliary Data
Buffer
Auxiliary data is that data contained in the MPEG headers required by
the system controller. Auxiliary data may be read through the system
controller port when the data is available. A small on-chip Auxiliary Data
FIFO allows the system controller to respond to an interrupt that indi-
cates that auxiliary data is available.
The Auxiliary Data FIFO is 128 bytes deep for Revision C and higher,
and 80 bytes deep for Revisions A and B. The Auxiliary Data Buffer in
described in detail in
Chapter 2. User data and auxiliary data should be
read from the corresponding FIFOs at every Data FIFO Ready Interrupt.
When set, the Data FIFO Ready (DFR) bit in the Group 3, Interrupt Reg-
ister 0 indicates there is data in the user data FIFO or the auxiliary data
FIFO.