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DP83820BVUW-AB View Datasheet(PDF) - National ->Texas Instruments

Part NameDescriptionManufacturer
DP83820BVUW-AB 10/100/1000 Mb/s PCI Ethernet Network Interface Controller National-Semiconductor
National ->Texas Instruments National-Semiconductor
DP83820BVUW-AB Datasheet PDF : 87 Pages
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3.0 Functional Description (Continued)
Figure 3-7 Master Write Operation
CLK
FRAMEN
AD[31:0]
C/BEN[3:0]
Addr Data
REQN
GNTN
IRDYN
TRDYN
DEVSELN
PAR
3.3.5 Configuration Access
Configuration register accesses are similar to Target reads
and writes in that they are single data word transfers and
are initiated by the system. For the system to initiate a
Configuration access, it must also generate IDSELN as
well as the correct Command (1010b or 1011b) during the
Address phase. The DP83820 will respond as it does
during Target operations.
Note: Configuration reads must be 32-bits wide, but writes may access individual
bytes.
3.4 Packet Buffering
The DP83820 incorporates two independent FIFOs for
transferring data to/from the system interface and from/to
the network. The FIFOs, providing temporary storage of
data, free the host system from the real-time demands of
the network.
The way in which the FIFOs are emptied and filled is
controlled by the FIFO threshold values in the TXCFG and
RXCFG registers (See Sections 4.2.12 and 4.2.16). These
values determine how full or empty the FIFOs must be
before the device requests the bus. Additionally, there is a
threshold value that determines how full the transmit FIFO
must be before beginning transmission. Once the DP83820
requests the bus, it will attempt to empty or fill the FIFOs as
allowed by the respective MXDMA settings in TXCFG and
RXCFG.
3.4.1 Transmit Buffer Manager
The buffer management scheme used on the DP83820
allows quick, simple and efficient use of the frame buffer
memory. The buffer management scheme uses separate
buffers and descriptors for packet information. This allows
effective transfers of data to the transmit buffer manager by
simply transferring the descriptor information to the
transmit queue. Refer to the Buffer Management section for
complete information.
The Tx Buffer Manager DMAs packet data from PCI
memory space and places it in the 8KB transmit FIFO, and
pulls data from the FIFO to send to the Tx MAC. Multiple
packets may be present in the FIFO, allowing packets to be
transmitted with minimum interframe gap. The way in which
the FIFO is emptied and filled is controlled by the FIFO
threshold values in the TXCFG register: FLTH (Tx Fill
Threshold), and DRTH (Tx Drain Threshold). Additionally,
once the DP83820 requests the bus, it will attempt to fill the
FIFO as allowed by the MXDMA setting in the TXCFG
register.
3.4.2 Transmit Priority Queueing
The Tx Buffer Manager process also supports priority
queueing of transmit packets. It handles this by drawing
from four separate descriptor lists to fill the internal FIFO. If
packets are available in the higher priority queues, they will
be loaded into the FIFO before those of lower priority.
3.4.3 Receive Buffer Manager
The Rx Buffer Manager uses the same buffer management
scheme as used for transmits. Refer to the Buffer
Management section for complete information.
The Rx Buffer Manager retrieves packet data from the Rx
MAC and places it in the 32KB receive data FIFO, and pulls
data from the FIFO for DMA to PCI memory space. The Rx
Buffer Manager maintains a status FIFO, allowing up to 32
packets to reside in the FIFO at once. Similar to the
transmit FIFO, the receive FIFO is controlled by the FIFO
threshold value in RXCFG:DRTH (Rx Drain Threshold).
This value determines the number of long words written
into the FIFO from the MAC unit before a DMA request for
system memory occurs. Once the DP83820 gets the bus, it
will continue to transfer the long words from the FIFO until
the data in the FIFO is less than one long word, or has
reached the end of the packet, or the max DMA burst size
is reached (RXCFG register:MXDMA).
3.4.4 Receive Priority Queueing
The Rx Buffer Manager process also supports priority
queueing of receive packets. It handles this by placing
packets on up to four separate descriptor lists when
emptying the internal FIFO. The Rx Buffer Manager uses
information in a VLAN tag to determine packet priority.
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