DP83901AV datasheet(15/62 Pages) NSC

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70 Packet Reception (Continued)

Enabling the SNIC On An Active Network

After the SNIC has been initialized the procedure for dis-

abling and then re-enabling the SNIC on the network is simi-

lar to handling Receive Buffer Ring overflow as described

previously

1 Program Command Register for page 0 (Command

2 Initialize Data Configuration Register (DCR)

3 Clear Remote Byte Count Registers (RBCR0 RBCR1)

4 Initialize Receive Configuration Register (RCR)

5 Place the SNIC in LOOPBACK mode 1 or 2 (Transmit

Configuration Register e 02H or 04H)

6 Initialize

Receive

Buffer

Ring

Boundary

Pointer

(BNDRY)

Page Start (PSTART)

and Page Stop

(PSTOP)

7 Clear Interrupt Status Register (ISR) by writing 0FFH to

8 Initialize Interrupt Mask Register (IMR)

9 Program Command Register for page 1 (Command

i) Initialize Physical Address Registers (PAR0 – PAR5)

ii) Initialize Multicast Address Registers (MAR0 – MAR7)

iii) Initialize CURRent pointer

10) Put SNIC in START mode (Command Register e 22H)

The local receive DMA is still not active since the SNIC

is in LOOPBACK

11) Initialize the Transmit Configuration for the intended val-

ue The SNIC is now ready for transmission and recep-

tion

END OF PACKET OPERATIONS

At the end of the packet the SNIC determines whether the

received packet is to be accepted or rejected It either

branches to a routine to store the Buffer Header or to anoth-

er routine that recovers the buffers used to store the packet

SUCCESSFUL RECEPTION

If the packet is successfully received the DMA is restored

to the first buffer used to store the packet (pointed to by the

Current Page Register) The DMA then stores the Receive

Status a Pointer to where the next packet will be stored

(Buffer 4) and the number of received bytes Note that the

remaining bytes in the last buffer are discarded and recep-

tion of the next packet begins on the next empty 256-byte

buffer boundary The Current Page Register is then initial-

ized to the next available buffer in the Buffer Ring (The

location of the next buffer had been previously calculated

and temporarily stored in an internal scratchpad register)

Termination of Received PacketPacket Accepted

TLF10469 – 12

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