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7.0 Packet Reception
(Continued)
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
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.
Linking Receive Buffer Pages
TL/F/11157 – 12
1) Check for
e
to PSTOP
2) Check for
e
to Boundary
16
Obsolete