CS6100 Amphion Semiconductor Ltd., CS6100 Datasheet - Page 3

• Manufacturer Part Number: CS6100
• Description: Motion JPEG Encoder
• Manufacturer: Amphion Semiconductor Ltd.

The adaptive bit rate control unit (BRC) applies a coefficient
thresholding technique for ensuring that the compressed
image size does not exceed a user defined bandwidth budget.
This particular feature of the CS6100 is essential for applica-
tions where the JPEG stream output from the CS6100 is to be
transmitted over a bandwidth-constrained data channel. The
BRC tracks the byte-count growth during the compression of
an image via feedback from the Huffman encoder in the VLE
block. The BRC adapts dynamically as the total image is
processed, applying different rules to selectively remove
(zero-out) coefficients in order to converge the actual com-
pressed image size and the ideal size. Further details on the
BRC mechanism are provided in the CS6100 Databook. The
CS6100 BRC features are a significant advancement over the
requirements set forth in the JPEG standard, yet the resultant
output stream is 100% compliant with the standard and can
be decoded by any standard-compliant JPEG decoder.
The variable length encoding unit (VLE) consists of both
the run length encoding unit (RLE) and the Huffman
encoder (HUFF). Data output by the BRC is buffered in
the ZigZag Memory (ZZMem) then loaded into the run
length encoder (RLE) unit. The RLE compresses the data
stream by converting the data to Run-Size pair data bytes.
Huffman encoding techniques are then applied to the stream
of Run-Size pairs to replace them with a corresponding code
read from a look-up table stored in the Huffman Table mem-
ory (HTMem). Huffman codes are designed to be uniquely
identifiable yet minimize the number of bits required to store
all the Run-Size codes for an image. The CS6100 can store
four user-defined Huffman Tables, two for DC coefficients
and two for AC coefficients, the DC and AC coefficients
being Huffman encoded separately. The compression pro-
duced by the VLE is data dependent thus latency can vary
from one block to the next.
ADAPTIVE BIT RATE CONTROL
VARIABLE LENGTH CODER
Figure 3: Bit Rate Control Illustration
The data stream generator unit (DSG) accepts the Huffman
encoded data stream from the VLE and packs the variable
length words into double-byte words. The double-byte
words are output over the JPEG output bus (JpgOut) when
requested by the external system. Additionally, the DSG
outputs JPEG file header information according to the parame-
ters set during configuration and under control of the JPEG
mask control port (JpgMask). The DSG also provides feed-
back to the BRC to enable the dynamic control of the com-
pression should this feature be selected by the system. The
latency of the DSG is variable and depends on the data
received from the VLE. When the last data for a frame is
received from the VLE, the double-byte word is padded
out and is immediately available for output.
The configuration and control interface unit (CCI) includes
an AutoParser that interprets configuration data, a configura-
tion memory (ConfigMem) for storing the full configuration
stream for later use as part of the JPEG output stream, and a
code control state machine (CodCtrl) that manages the opera-
tion of the CS6100.
DATA STREAM GENERATOR
& CONTROL INTERFACE
CONFIGURATION
3