DP83902AVF datasheet(16/70 Pages) NSC

16 / 70 page

70 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

TLF11157 – 12

1) Check for e to PSTOP

2) Check for e to Boundary

DP83902AVF Datenblatt(PDF) 16 Page - National Semiconductor (TI)