GDC21D401B Datasheet, PDF (12/28 Pages) Hynix Semiconductor – Video Decoder

5.7 Bitstream Buffer Over/Underflow
The bitsream buffer should not be overflowed or
underflowed in proper operation. When bitstream
buffer is overflowed, video bitstream input is
disabled during overflow. At the beginning of each
picture, buffer underflow is checked. If the
bitstream buffer doesn’t include 1 picture
bitstream, decoding is paused until this buffer is
filled with 1 picture bitstream.
5.8 VLD (Variable Length Decoder)
The VLD executes the variable length decoding of
MPEG-2 MP@HL. It is composed of sequence
syntax parsing and code decoding. Headers, IDCT
coefficients, and motion vectors are generated from
input video bitstream by the VLD.
5.9 Inverse Quantization
For decoding a macroblock, various parameters
are transmitted to IQ block and MC block in
sequence of decoding syntax from the VLD.
Coefficient data transmitted to IQ block is
multiplied by quantization matrix and quantization
scale. Quantized coefficients are stored in two
coefficient buffers, and if a request from MC block
occurs, the buffer outputs 4 coefficients in parallel.
Inverse scan processing is performed in the
coefficient buffer by varying read/write address
according to scan type.
GDC21D401B
5.10 IDCT (Inverse Discrete Cosine
Transform)
Coefficient data from IQ block is transmitted to
IDCT block. IDCT block transforms these
coefficients to pixel data or differential pixel data
which have the values in the range of -256 to 255.
For one 8x8 DCT block, the elapse time through
IDCT block is a 30-VDCLK period. In the IDCT
block, 8 adjacent coefficients are processed in
parallel. The maximum transform speed of the
IDCT block is 1 VDCLK x 4 Sample/sec. This
speed is sufficient for decoding 1920x1088 30Hz
frame data.
5.11 MC(Motion Compensation)
Motion Compensation Block restores macroblocks
by using macroblock difference data from IDCT
block and reference data which are read from
external SDRAM. Address Generation Block in
the MC generates SDRAM address by
transforming macroblock address and motion
vector to row/column address of SDRAM. The
MC block supports all motion types of frames and
field pictures. Motion vector range decoded in the
MC has the range of f_code=9 for horizontal
motion vector and f_code=8 for vertical motion
vector. Reconstructed macroblock in the MC block
is stored in the external frame memory for I or P
picture, but in the case of B picture, decoded
macroblock is transmitted directly to the VDP
without being stored in the frame memory.
Because reordering occurs in I or P picture
decoding, macroblock data to be displayed is read
from reference frame memory and is transmitted to
the VDP in the form of macroblock.
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