dp83902a National Semiconductor Corporation, dp83902a Datasheet - Page 16

• Manufacturer Part Number: dp83902a
• Description: St-nictm Serial Network Interface Controller For Twisted Pair
• Manufacturer: National Semiconductor Corporation

7 0 Packet Reception
LINKING RECEIVE BUFFER PAGES
If the length of the packet exhausts the first 256-byte buffer
the DMA performs a forward link to the next buffer to store
the remainder of the packet For a maximum length packet
the buffer logic will link six buffers to store the entire packet
Buffers cannot be skipped when linking therefore a packet
will always be stored in contiguous buffers Before the next
buffer can be linked the Buffer Management Logic per-
forms two comparisons The first comparison tests for
equality between the DMA address of the next buffer and
the contents of the Page Stop Register If the buffer ad-
dress equals the Page Stop Register the buffer manage-
ment logic will restore the DMA to the first buffer in the
1) Check for
2) Check for
e
e
to PSTOP
to Boundary
(Continued)
Linking Receive Buffer Pages
16
Receive Buffer Ring value programmed in the Page Start
Address Register The second comparison tests for equality
between the DMA address of the next buffer address and
the contents of the Boundary Pointer Register If the two
values are equal the reception is aborted The Boundary
Pointer Register can be used to protect against overwriting
any area in the receive buffer ring that has not yet been
read When linking buffers buffer management will never
cross this pointer effectively avoiding any overwrites If the
buffer address does not match either the Boundary Pointer
or Page Stop Address the link to the next buffer is per-
formed
TL F 11157 – 12