DP83902A datasheet(21/70 Pages) NSC

21 / 70 page

70 Packet Reception (Continued)

REMOVING PACKETS FROM THE RING

Packets are removed from the ring using the Remote DMA

or an external device When using the Remote DMA the

Send Packet command can be used This programs the Re-

mote DMA to automatically remove the received packet

pointed to by the Boundary Pointer At the end of the trans-

fer the ST-NIC moves the Boundary Pointer freeing addi-

tional buffers for reception The Boundary Pointer can also

be moved manually by programming the Boundary Register

The ST-NIC knows the difference between an empty buffer

ring and a full buffer ring This situation is seen when the

Boundary Pointer (BNDRY) and the Current Page Pointer

(CURR) point to the same address If BNDRY caught up

with CURR the buffer is empty and if CURR caught up with

BNDRY the buffer is full

STORAGE FORMAT FOR RECEIVED PACKETS

The following diagrams describe the format for how re-

ceived packets are placed into memory by the local DMA

channel These modes are selected in the Data Configura-

tion Register

AD15

AD8 AD7

AD0

Next Packet Pointer

Receive Status

Receive Byte Count 1

Receive Byte Count 0

Byte 2

Byte 1

BOS e 0 WTS e 1 in Data Configuration Register This format is used with

Series 32xxx or 680x0 processors

AD15

AD8 AD7

AD0

Next Packet Pointer

Receive Status

Receive Byte Count 0

Receive Byte Count 1

Byte 1

Byte 2

BOS e 1 WTS e 1 in Data Configuration Register This format is used with

680x0 type processors (Note The Receive Count ordering remains the

same for BOS e 0or1 )

Receive Status

Next Packet Pointer

Receive Byte Count 0

Receive Byte Count 1

Byte 0

Byte 1

BOS e 0 WTS e 0 in Data Configuration Register This format is used with

general 8-bit processors

1st Received Packet Removed by Remote DMA

TLF11157 – 16

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