PLX Technology’s ExpressLane PCI Express switches not only incorporate a four-channel DMA engine that can offload memory transfer chores from the host, they also eliminate the need for DMA support on the host or its support chips (see the figure). The feature is implemented in the 16-lane/16-port PEX 8619, the 12-lane/12-port PEX 8615, and the eight-lane/eight-port PEX 8609.
The PCI Express Gen 2-compliant devices have configurable ports ranging from x1 to x4 and x8 on the PEX 8619. They support quality of service (QoS) via a pair of virtual channels per port, spread-spectrum clock isolation via dual clock domains, and end-to-end guaranteed data integrity.
The descriptor-based DMA channels can handle transfer sizes up to 128 Mbytes and 32- and 64-bit transfers between devices or memory. The 256 on-chip descriptors can be stored in memory. Each channel supports QoS. One channel alone can saturate a 4-Gbyte/s x8 link.
The PEX 8619, PEX 8615, and PEX 8609 start at $28.55, $22.25, and $14.25 respectively.