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DP83901AV 数据表(PDF) 10 Page - National Semiconductor (TI) |
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DP83901AV 数据表(HTML) 10 Page - National Semiconductor (TI) |
10 / 62 page 70 Packet Reception The Local DMA receive channel uses a Buffer Ring Struc- ture comprised of a series of contiguous fixed length 256-byte (128 word) buffers for storage of received packets The location of the Receive Buffer Ring is programmed in two registers a Page Start and a Page Stop Register Ether- net packets consist of a distribution of shorter link control packets and longer data packets the 256-byte buffer length provides a good compromise between short packets and longer packets to most efficiently use memory In addition these buffers provide memory resources for storage of back-to-back packets in loaded networks The assignment of buffers for storing packets is controlled by Buffer Man- agement Logic in the SNIC The Buffer Management Logic provides three basic functions linking receive buffers for long packets recovery of buffers when a packet is rejected and recirculation of buffer pages that have been read by the host At initialization a portion of the 64 kbyte (or 32k word) ad- dress space is reserved for the receive buffer ring Two 8-bit registers The Page Start Address Register (PSTART) and the Page Stop Address Register (PSTOP) define the physi- cal boundaries of where the buffers reside The SNIC treats the list of buffers as a logical ring whenever the DMA ad- dress reaches the Page Stop Address the DMA is reset to the Page Start Address NIC Receive Buffer Ring TLF10469 – 7 10 |
类似零件编号 - DP83901AV |
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类似说明 - DP83901AV |
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