Image Transfer

The processed and formatted image data are transferred into a surface over the PCI Express bus using a DMA engine.

Note. In the MultiCam driver, a surface is the physical memory space allocated into the host PC memory for the storage of one image.

The transferred image is stored in the destination surface in a progressive-scan order:

The first pixel (top-left corner) of the transferred image is stored at the first memory location of the surface (at 0).
The first pixels of the subsequent lines are stored at a byte address that is a multiple of the surface pitch.

Surface Pitch

The MultiCam driver establishes a default surface pitch that corresponds to the amount of bytes required to store one pixel row of the image data. You may increase this value if the application requires it.

Surface Size

The MultiCam driver establishes a default surface size that corresponds to the amount of bytes required to store all the rows of the image data. You may increase this value if its application requires it.

Extended Addressing Capabilities

This board is capable of transferring image data anywhere into the physical memory of the system.

Automatic DMA Descriptors Loading

This board implements an automatic mechanism for the loading of the DMA descriptors from the host PC memory to the DMA descriptor section of the on-board memory.

The DMA descriptors lists can then be prepared and stored into the host PC memory; the automatic loader pre-fetches the descriptors such that they are available for the DMA engine when it needs them.

Notes

The transfer of the descriptors is performed with the second DMA engine, it doesn't require any CPU work.
The transfer of the descriptors does not impact the available bandwidth on the PCI Express link for image transfer since it conveys data on the opposite direction.

Transfer Rate

Grablink Base sustains image data transfer over the PCI Express bus:

Up to 200 megabytes/s for a PCI Express payload size of 256 bytes.
Up to 180 megabytes/s for a PCI Express payload size of 128 bytes.

Note. The effective data rate depends on the performance of the PCI Express Link.