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ZR36050

JPEG IMAGE COMPRESSION PROCESSOR

Zoran Corporation 

ADVANCE INFORMATION

ZR36050

contains the marker segments that the Encoding/Decoding Unit

extracted from the compressed data.

The Internal Memory space also contains a write-only virtual

register (at address 0) by means of which the host issues the GO

command to start operation. In Slave mode Compressed Data

Transfer, the host reads the compressed data from or writes it

into, a Compressed Data Input/Output register. That is also

mapped into the Internal Memory space.

PROGRAMMING THE ZR36050

The host configures the processing units and interfaces of the

ZR36050 for the desired operation by means of the Control Reg-

isters and Marker Segments sections of the Internal Memory.

Many of the parameters that determine the proper operating con-

figuration of a JPEG encoder or decoder are embedded in the

marker segments that are included with JPEG compressed

image data. For example, the JPEG frame header specifies the

number of data units (blocks or samples) of each image compo-

nent in the MCU, and the scan header specifies the number of

image components in the scan. This information is essential for

the Encoding/Decoding Unit to perform the quantization and

Huffman coding correctly. The ZR36050 decodes these param-

eters automatically from marker segments in JPEG format. In

compression, these marker segments must be written in the

Marker Segments Section of Internal Memory by the host, before

it initiates the compression. In expansion, the marker segments

are part of the compressed data; the Encoding/Decoding Unit

copies them from the Code Buffer into Internal Memory before

decoding the parameters.

The basic operating mode and interface configuration are spec-

ified in the MODE and HARDWARE control registers. For an

image expansion operation, these and the INT_REQ registers

are the only ones that need to be initialized. Other control regis-

ters, such as the OPTIONS and MARKERS_EN registers, are

used only in compression operation or Table Preload modes.

In addition to the frame (SOFn) and scan (SOSn) header marker

segments, the Internal Memory has space allocated for the

Define Restart Interval (DRI), Define Number of Lines (DNL),

Define Quantization Tables (DQT), Define Huffman Tables

(DHT), Application (APP) and Comment (COM) marker seg-

ments, which can optionally be included with the compressed

image data in compression. The MARKERS_EN register

provides the means by which the host can specify which of the

optional marker segments are to be included in the compressed

data.

For further details on programming, refer to the section “INTER-

NAL MEMORY FORMAT.”

STATUS AND INTERRUPTS

The ZR36050 has two status registers, that are readable by the

host and provide feedback on the various events occurring

during an encoding or decoding operation. Associated with the

status registers are two interrupt enable registers, the bits of

which correspond to those of the status registers. If the host sets

an interrupt enable bit, the ZR36050 will interrupt it when the cor-

responding status bit becomes active and stops processing. The

host can then take appropriate action before commanding the

ZR36050 to continue processing (by means of the GO

command).

The STATUS_0 and INT_REQ_0 register bits correspond to the

names of JPEG marker segments. In a decoding operation, the

ZR36050 sets a STATUS_0 bit when the corresponding marker

segment has been extracted from the compressed data stream

and written in the Internal Memory. If the INT_REQ_0 bit was

also set, the host can read out the marker segment content

before continuing.

The APP and COM bits of STATUS_0 have a special mecha-

nism associated with them, that makes it possible for the host to

read out a segment of any length, even though there are only 64

bytes allocated to each of the APP and COM segments in

Internal Memory. If the corresponding interrupt is enabled, and

the segment is longer than 64 bytes, the ZR36050 stops after

writing each 64 byte portion in Internal Memory, and waits for a

GO command. The last portion may have fewer than 64 bytes.

The APP and COM bits of STATUS_0 are also used, with a

similar mechanism, to include APP or COM segments longer

than 64 bytes in the compressed data. In this case, the host

programs the APP or COM bit of the MARKERS_EN register,

writes the first 64 byte portion of the segment in the Internal

Memory, and enables the interrupt in the INT_REQ_0 register.

When the ZR36050 has transferred the portion to the Code

Buffer, it stops as before, if the length parameter indicated a

segment longer than 64 bytes. The host can then write the next

64 byte portion in the Internal Memory, and repeat the procedure

until the whole segment is transferred. The ZR36050 does not

stop after transferring the last portion of 64 or fewer bytes.

The STATUS_1 and INT_REQ_1 register bits indicate miscella-

neous conditions: readiness for data or new optional marker

segments, end of process, and overflow conditions. A special bit

in STATUS_1, consisting of the logical OR of all the bits of

STATUS_0, permits the host to determine the type of event that

caused an interrupt, by reading only the STATUS_1 register.

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