| 摘要 |
An improved network interface card (NIC) allows received ATM cells of a protocol data unit (PDU) to be grouped by a programmable size and then sent via an efficient DMA transfer to the host computer memory. Sizes of the blocks of data transferred from the NIC to the host memory are optimized for virtual circuit type, PDU type, NIC memory constraints, bus bandwidth, maximum DMA transfer rate, etc. A destination host receives cells for multiple virtual circuits in an interleaved fashion for various PDUs. The received cells are divided up by virtual circuit; cells for one virtual circuit are stored in a linked list of slots, where each slot contains one ATM cell. Cells from each virtual circuit are linked together in a group, with a separate linked list of cells for each virtual circuit. A programmable group size parameter defines how many cells are grouped together in the linked list before the group is dispatched to system memory in the host computer. When the number of cells in a linked list reaches this programmable group size, or when the last cell of a PDU arrives, the linked list of cells is sent via DMA transfer to host memory. The DMA transfer uses buffers in the host computer memory to complete the PDU reassembly process. Groups of cells are transferred from the NIC to the host computer buffers as a single group. If a buffer fills up, or a PDU is complete, a new host computer buffer is used for additional portions of that PDU or for a subsequent PDU.
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