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ZR36050

JPEG IMAGE COMPRESSION PROCESSOR

Zoran Corporation 

ADVANCE INFORMATION

ZR36050

Any encoding mode operation starts in the same way, regardless

of the specific operating mode selected:

s Initially, after RESET is deactivated, the ZR36050 is in the

Idle state, awaiting the GO command, with the END and

STOP signal pins active. Alternatively, it could be in the Idle

state as a result of the completion of a previous operation.

s Before the host starts the ZR36050 by issuing a GO

command, the Control Registers must be initialized to their

appropriate states, and the Marker Segments Section of

Internal Memory must contain the JPEG marker segments

needed for the desired operation. If the registers and marker

segments are correctly configured from a previous operation,

no action is required. Otherwise, the host can write the

initialization data in the registers and marker segments at

any time while the device is in the Idle state.

s After the host issues the GO command, the ZR36050 clears

the END status bit, reads the Control Registers and initializes

itself for the selected operating mode and interface

configuration.

The continuation of the operating sequence from this point

depends on the operating mode selected.

When a status (STATUS_0 or STATUS_1) register bit becomes

active, the ZR36050 normally continues processing unless the

corresponding interrupt request enable (INT_REQ_0 or

INT_REQ_1) register bit was also set by the host. If it was set,

the ZR36050 activates the INT output signal, stops processing

and waits for the host to intervene. INT is deactivated when the

host reads the relevant status register, and the ZR36050 contin-

ues processing after the host issues a GO command. If the

TCVOVF or DATOVF status bits are set, the ZR36050 aborts

processing and goes into the Idle state. The TCVOVF and

DATOVF bits in the INT_REQ_1 register must be set to “1” at the

beginning of an encoding operation.

Compression Pass

s The ZR36050 processes the SOF marker segment and the

optional marker segments selected by the MARKERS_EN

register, and transfers them to the compressed data after the

SOI marker.

If the frame marker is SOF3, the ZR36050 switches to Loss-

less encoding operation.

s Before processing the SOS marker, the ZR36050 sets the

RFM status bit. If the corresponding interrupt request is

enabled, the ZR36050 activates INT and stops processing.

After receiving the GO command, it re-reads the

INT_REQ_(1,2) and MARKERS_EN registers and transfers

the specified marker segments to the compressed data. If

more that one scan is required, as specified in the OPTIONS

register, the ZR36050 sets RFM as above before processing

each SOS marker, and re-reads MARKERS_EN after

receiving the GO command. The host can use this

mechanism to insert optional marker segments before each

scan, if required. Also, since the Internal Memory has space

for only four SOS marker segments, the same mechanism is

used if more than four scans are required. In this case, when

the ZR36050 stops before the fifth scan, the host can update

the scan marker segments in the internal memory before

continuing.

If the MARKERS_EN register specifies an APP (or COM)

segment, and the desired segment length is more that 64

bytes, it can be transferred in 64 byte sections if the APP (or

COM) interrupt request bit is enabled in the INT_REQ_0 reg-

ister. When initializing the Internal Memory, the host writes

the first 64 bytes of the segment. Each time the Encoding

Unit has completed transfer of a 64 byte section to the Code

Buffer, the ZR36050 sets the APP (or COM) status bit, acti-

vates INT, and waits for the host to write the next section in

the Internal Memory. After transferring the last section of 64

or fewer bytes, the ZR36050 continues processing without

setting the status bit or activating the interrupt.

s When the ZR36050 processes the SOS marker for the first

scan, it calculates the number of blocks (or samples for

Lossless compression) of each component of the scan in the

MCU, and transfers the scan marker segment to the Code

Buffer. When it is ready to accept image data, it sets the RFD

status bit, and deactivates STOP. The system can then start

supplying image data for the first scan.

s The ZR36050 processes the image data and outputs the

compressed data. In JPEG Baseline compression, the DCT

Unit computes the DCT of each block, and the Encoding Unit

quantizes the transformed samples and Huffman codes the

quantized samples. In Lossless compression, the Encoding

Unit calculates the prediction for each sample, and Huffman

codes the predicted value. It writes the compressed data in

the Code Buffer, from where it is sent to the compressed data

interface or the host interface, as specified in the

HARDWARE control register.

In a Compression Pass with Bit Rate Control, the ZR36050

also computes the activity measure of each block before en-

coding it, and allocates a variable number of compressed

data bits to the block, based on the Allocation Factor but not

exceeding the number specified in the MBCV register. If the

encoded block requires more bits than the allocated number,

the ZR36050 truncates the compressed data for the block in

a manner that preserves JPEG Baseline compatibility.

If the OVF bit of the OPTIONS register is set, and the accu-

mulated code volume exceeds the limit specified by the

TCV_NET register at any time during the encoding, the En-

coding Unit stops writing compressed data into the Code

Buffer, and the ZR36050 aborts the Compression Pass com-

pletely, sets the TCVOVF status bit, and goes into the Idle

state.

s When the system activates the EOS input, indicating the last

data sample of the scan, the ZR36050 activates STOP.

s At the end of the first scan only, if the DNL bit of the

MARKERS_EN register is set, the Encoding Unit transfers

the DNL marker segment from Internal Memory to the Code

Buffer. DNL is disregarded in all other scans.

s If more that one scan is required, as indicated by the

OPTIONS register, the ZR36050 sets the RFM status bit and

compresses the second scan.

s After completing the last scan, the ZR36050 calculates a

New Scale Factor (NSF) and writes the NSF, Accumulated

Code Volume, Truncated Accumulated Code Volume (if Bit

Rate Control is used), and Total Activity in the respective

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