This device moves data between the local PCI bus and the high-speed memory bus. It is specifically designed to move image data efficiently and at high speeds. It is a PCI device and so is accessible to the i960RP and, with the proper i960 software and bridge configuration, to the host as well.
The memory bus DMA controller function of the Image Memory Controller is not the same as the DMA controller that the i960RP includes on-chip. The i960RP DMA controller only supports transfers to or from its local memory. The Image Memory Controller only has access to PCI accessible memory, and to the memory and devices on the high speed memory bus.
The Image Memory Controller also assumes PCI arbitration tasks for the tertiary PCI bus. The arbitration function replaces that of the DEC bridge, which has its arbitration capabilities turned off, because of limitations in the arbiter in the DEC 21152.