Data Forwarding Principles
Data forwarding
A DF-capable card, such as the
The image data packets embedded in the serial bit stream on connections A, B, C, D of the CoaXPress Host connector are forwarded to the connections FA, FB, FC, FD of the CoaXPress Data Forwarding connector.
The serial bit streams are re-timed to operate always at CXP-6 speed regardless the link speed of the camera. Therefore, idle characters are, when necessary, removed or added in the bit stream. Addition or removal of idle characters doesn't affect the payload. Image data are preserved, including CRC's. For proper operation of data forwarding, it is mandatory that the camera inserts one IDLE word at least once every 100 words as required by the Coaxlink 1.1 standard §8.2.5.1.
The image data are retransmitted with a negligible latency: typically, a few periods of the 32-bit character transmission time.
Note: The Data Forwarding output port doesn't comply with the specification of a CoaXPress Device! It can only feed another
Data Forwarding Chain
A DF-chain is composed of 2 or more data-forwarding capable cards where the CoaXPress Data Forwarding connector of one card is connected to the CoaXPress Host connector of the next card using a set of 1, 2 or 4 coaxial cables named DF-bridge.
Note: There are no specified upper limit to the number of cards in a DF-chain.
The camera is attached to the CoaXPress Host connector of the first card of the DF-chain, this card is named DF-master. The other cards, of the DF-chain are named DF-slaves. The CoaXPress Data Forwarding connector of the last DF-slave card is left unconnected.
CoaXPress Link discovery and configuration
The DF-master card is responsible for the discovery and the configuration of the CoaXPress Link of the camera.
The CoaXPress Host Interface of the DF-slaves are automatically configured with the same number of connections as discovered by the DF-Master.
For instance if the camera uses two connections, only two connections are required for every DF-bridge.
Firmware variants
The firmware variant to install on the DF-master must be selected according to the camera type:
| ● | For an area-scan camera, install the 1-camera firmware variant. |
| ● | For a line-scan camera, install the 1-camera, line-scan firmware variant. |
The firmware variant to install on the DF-slaves must match the firmware variant installed on the DF-master:
| ● | When the 1-camera firmware variant is installed on the DF-master, install the 1-df-camera firmware
variant on all DF-slaves. |
| ● | When 1-camera, line-scan firmware variant is installed on the DF-master, install the 1-df-camera, line-scan
firmware variant on all DF-slaves. |
Data Acquisition Control
For correct operation of data forwarding, the application must respect the following rules:
| ● | The data acquisition must be activated on all the DF-slaves before being activated on the DF-master. |
| ● | The data acquisition must be de-activated on the DF-master before being de-activated on the DF-slaves. |
For line-scan applications only, a start-of-scan and end-of-scan synchronization mechanism is implemented to ensure that all the cards of the DF-chain can capture the same lines of image data.
Refer to Line-scan Triggers Synchronization for more info.
Camera Cycle Control
If required by the application, the DF-master card is responsible for the elaboration of the CoaXPress Host-to-Device trigger. This is achieved in the same way as for non-data-forwarding Coaxlink cards.
Refer to CoaXPress Host To Device Trigger for more details.