![background image](http://html.mh-extra.com/html/national-semiconductor/st-nic-dp83902a/st-nic-dp83902a_manual_710381016.webp)
7.0 Packet Reception
(Continued)
INITIALIZATION OF THE BUFFER RING
Two static registers and two working registers control the
operation of the Buffer Ring. These are the Page Start Reg-
ister, Page Stop Register (both described previously), the
Current Page Register and the Boundary Pointer Register.
The Current Page Register points to the first buffer used to
store a packet and is used to restore the DMA for writing
status to the Buffer Ring or for restoring the DMA address in
the event of a Runt packet, a CRC, or Frame Alignment
error. The Boundary Register points to the first packet in the
Ring not yet read by the host. If the local DMA address ever
reaches the Boundary, reception is aborted. The Boundary
Pointer is also used to initialize the Remote DMA for remov-
ing a packet and is advanced when a packet is removed. A
simple analogy to remember the function of these registers
is that the Current Page Register acts as a Write Pointer and
the Boundary Pointer acts as a Read Pointer.
Note:
At initialization, the Page Start Register value should be loaded into
both Current Page Register and the Boundary Pointer Register.
Note:
The Page Start Register must not be initialized to 00H.
BEGINNING OF RECEPTION
When the first packet begins arriving the ST-NIC begins
storing the packet at the location pointed to by the Current
Page Register. An offset of 4 bytes is saved in this first
buffer to allow room for storing receive status correspond-
ing to this packet.
Buffer Ring at Initialization
TL/F/11157 – 10
Received Packet Enters the Buffer Pages
TL/F/11157 – 11
15
Obsolete