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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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DP83902A датащи(PDF) 14 Page - National Semiconductor (TI) |
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DP83902A датащи(HTML) 14 Page - National Semiconductor (TI) |
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14 / 70 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 ST-NIC The Buffer Management Log- ic 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 ST-NIC treats the list of buffers as a logical ring whenever the DMA address reaches the Page Stop Address the DMA is reset to the Page Start Address ST-NIC Receive Buffer Ring TLF11157 – 9 14 |
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