Pleora Technologies iPORT CL-Ten, User Manual, Page: 48 / 72

44 iPORT Advanced Features User Guide
About the Extended Chunk Mode Feature
The extended chunk mode feature allows you to append metadata to some of the payload types, such as
an image payload, as chunk data. For example, when the extended chunk feature is enabled, you can
attach the position of the conveyor belt (metadata) to the image of the product on the conveyor belt.
Metadata is attached to the data block as “chunk data”, which is also referred to simply as “chunks”.
A chunk includes the chunk data and chunk tags (CID and length fields).
The table below describes the general structure of any chunk.
There are two sources of metadata supported by Pleora’s video interfaces: metadata generated by the
camera and metadata generated by the video interface.
MetaData Generated by the Camera
Cameras can send metadata containing camera-specific information to the video interface using the
MVAL (Metadata Valid) signal, which is supplied by the camera. The MVAL signal should be connected
to the SPARE signal pin on the pixel bus of the video interface.
The MVAL signal functions in a similar manner as the LVAL signal and is only valid when the FVAL
signal is valid.
Metadata must be transmitted on the pixel bus at the end of the image data. All image lines (LVAL) will
be dropped after a first MVAL assertion.
The following timing diagram provides an example of image data combined with metadata in a single
frame. One image payload type block contains three chunks: image chunk data and two metadata chunks.
Table 11: Chunk Structure Descriptions
Position Format Size Description
0 data K Bytes The data transported by the chunk.
This section must be a multiple of 4 bytes. If it is not, the data must
be padded with zeros to a multiple of four bytes such that K is a
multiple of 4 bytes. This ensures
CID and length fields are 32-bit
aligned within the chunk.
Endianness of the chunk data itself is defined in the XML device
description file.
K CID 4 bytes The chunk identifier.
The CID tag MUST use network byte order (big-endian).
K+4 length 4 bytes The length of the data (in bytes, must be a multiple of 4).
The length tag MUST use network byte order (big-endian).