CS6150 Amphion Semiconductor Ltd., CS6150 Datasheet - Page 6

• Manufacturer Part Number: CS6150
• Description: Motion JPEG Decoder
• Manufacturer: Amphion Semiconductor Ltd.

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The core enters the Marker Decode state when it receives the
first byte of the decode stream and remains there until it
decodes either an SOS or EOI marker. If it decodes an SOS
marker and has already received all the other information
needed to decode the scan, such as the Huffman tables, it
enters Entropy Decode state, otherwise it will assert an error
flag on the CodFlags output port and will stop accepting
data. If it receives an EOI it enters Idle state. The JpgInProg
output [CodFlags(0)] is asserted when the core starts to
process input JpgIn and is de-asserted when the EOI marker
has been loaded into the core on the JpgIn input. If the core
enters Marker Decode state from Idle state it expects to
receive an SOI as the first input and will discard all input
until an SOI is received. When recovering from an error in
the decode stream, this allows the core to discard the end of
corrupt stream and to locate the start of the new stream. This
synchronization feature could be useful if the decode stream
is arriving from a noisy channel in an MJPEG system and
means that the system does not have to locate the start of the
stream for the core.
When in Marker Decode state the core automatically detects
the JPEG marker segments listed in Table 3.
After detecting a segment the core decodes and stores the
information in the segment and checks that the information
is valid. If the information contains an error, then the core
will assert an error flag on the DecFlags output port and will
stop accepting data. The error can be cleared by asserting
RSTn or CLR.
As the segments are being decoded from the decode-stream
they can also be output by the core on port DecJpg, and the
user can select the ones that are actually output by setting
bits on the JPEG Mask port according to Table 6. This could
Loading of the compressed JPEG input image data is per-
formed using the JpgIn interface. The data stream is input to
CS6150 via the JpgIn[7:0] port. This stream must also be
accompanied by a data valid signal, JpgInStrb, which must
be asserted coincident with all valid samples. The data inter-
face operates synchronously, reading a compressed JPEG
Figure 5: JPEG Data Stream Input Interface Timing
JpgInRdy (O)
JpgInStrb (I)
CS6150
JpgIn (I)
MARKER DECODE STATE
DECODER OPERATION
M o t i o n J P E G D e c o d e r
JPEG DATA STREAM INPUT PORT
be used, for example, as a simple method for the user to gain
access to the information contained in the APP markers with-
out having to parse the data stream.
The core enters Entropy Decode state after decoding an SOS
from the decode stream. In Entropy Decode state it decodes
the pixel data from the entropy-coded segments, automatically
selecting the correct Huffman and quantization tables to use
for each component. If an error is detected in the entropy
coded data the core will assert DecHfError (DecFlags[7]), and
will attempt to recover by discarding entropy coded data up
to the next Restart Marker or the end of the image, whilst
still producing the expected amount of pixel data. The
DecHfError signal is cleared by RSTn or CLR and by the
start of a new decode-stream and, as a result, the core does
not need the user to respond to the DecHfError signal. The
DecInProg signal will be asserted whilst decoding a scan.
Table 3: Jpg Segments
data sample at the rising edge of every clock cycle when
enabled to do so. The JpgInRdy output from the core controls
the flow of data on the JpgIn bus and, if necessary, acts as a
request to halt the input of data for an arbitrary time interval.
The functional timing for the JPEG data stream input inter-
face is shown in Figure 5.
SEGMENT
SOF0
Input data is held on the JpgIn Input as JpgInRdy is low
APPn
COM
SOS
DQT
DHT
DNL
DRI
ENTROPY DECODE STATE
Application segment, n=0…F
Define quantization table(s)
Baseline frame definition
Define Huffman table(s)
Define number of lines
Define restart interval
DESCRIPTION
Start of scan
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