tm1300 NXP Semiconductors, tm1300 Datasheet - Page 227

• Manufacturer Part Number: tm1300
• Description: Tm-1300 Media Processor
• Manufacturer: NXP Semiconductors

Variable Length Decoder
15.1
The variable length decoder (VLD) unit Huffman-de-
codes MPEG-1 and MPEG-2 (Main Profile) video bit-
streams[1-3]. This chapter describes a programmers
view of the VLD.
The VLD reads an MPEG stream from SDRAM, decodes
the bitstream under the control of DSPCPU and outputs
two data streams. The output data streams contain mac-
roblock header information and the run-length encoded
DCT coefficients. The output data streams are stored in
the SDRAM buffers.
The VLD unit, operates independently during the slice
decoding process. The remaining decoding of the MPEG
stream is carried out by the DSPCPU.
15.2
Enabled by the DSPCPU, the VLD unit can be initialized
by hardware or software reset operations. Hardware re-
Figure 15-1. VLD block diagram
HWY_BUS
VLD OVERVIEW
VLD OPERATION
Control
64 Bytes
Interrupt
64 Bytes
MMIO &
CONF REGs
Hdr WR FIFO
Macroblock
Run-Level
WR FIFO
RD Buffer
64 Bytes
ENGINE
DMA
status
status
Control
FLOW
VLD
SHIFTER
escape_codes
set is provided by the external TRI_RESET# pin. Soft-
ware reset is provided by one of the VLD commands.
The DSPCPU controls the VLD through the VLD com-
mand register. There are five commands supported by
the VLD:
• Shift the bitstream by some number of bits (a maxi-
• Search for the next start code
• Reset the VLD
• Parse some number of macroblocks
• Flush VLD output buffers to SDRAM
The normal mode of operation will be for the DSPCPU to
request that the VLD to parse some number of macrob-
locks. Once the VLD has begun parsing macroblocks, it
may stop for any one of the following reasons:
• The command was completed with no exceptions
• A start code was detected
• An error was encountered in the bitstream
PRODUCT SPECIFICATION
mum of 15-bit shift)
by Gene Pinkston and Selliah Rathnam
start_code_
detector
mb_addr
mb_type
dct_chr
dctcoef
dctcoef
motion
dmv &
dct_lum
Chapter 15
cbp
(1)
(0)
15-1