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поискавой системы для электроныых деталей |
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поискавой системы для электроныых деталей |
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DP83821 датащи(PDF) 25 Page - National Semiconductor (TI) |
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DP83821 датащи(HTML) 25 Page - National Semiconductor (TI) |
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25 / 86 page  3.0 Functional Description (Continued) 25 www.national.com 3.13.3 Transmit Architecture The Transmit architecture can support a single transmit queue, or can support multiple transmit queues for handling priority traffic. The following figures illustrate the transmit architecture of the DP83821 Ethernet Controller with and without Priority Queueing. Figure 3-14 Transmit Architecture without Priority Queueing Without Priority Queueing, the device will draw packets from a single Descriptor list. Only one descriptor pointer is required. When the CR:TXEN bit is set to 1 (regardless of the current state), and the DP83821 transmitter is idle, then DP83821 will read the contents of the current transmit descriptor into the TxDescCache. The DP83821’s TxDescCache can hold a single fragment pointer/count combination. Figure 3-15 Transmit Architecture with Priority Queueing With Priority Queueing, the device will draw packets from up to 4 Descriptor lists. The device has four descriptor pointers and associated control logic to keep track of when descriptors are available with valid packet information. In this case, pulsing CR:TXEN with CR:TXPRI[p] set will indicate to the DP83821 that a descriptor is available for descriptor queue of priority ‘p’. Based on the priority algorithm in use, the device will draw from the current highest priority descriptor that has packets available for transmission. There is no reordering of packets once they are queued within the internal FIFO. Transmit Descriptor Current Tx Desc Ptr Software/Memory Hardware Tx Data FIFO link bufptr cmdsts cmdsts Tx DMA bufptr Packet TxHead link Tx Desc Cache link bufptr cmdsts Packet link bufptr cmdsts Packet Transmit Descriptor Current Tx Desc Ptr Software/Memory Hardware Tx Data FIFO link bufptr cmdsts cmdsts Tx DMA bufptr TxHead link Tx Desc Cache link bufptr cmdsts link bufptr cmdsts link bufptr cmdsts link bufptr cmdsts link bufptr cmdsts link bufptr cmdsts link bufptr cmdsts link bufptr cmdsts link bufptr cmdsts link bufptr cmdsts link bufptr cmdsts TXDP1 TXDP2 TXDP3 TXDP4 Q0 Q1 Q2 Q3 |
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