dp83902a National Semiconductor Corporation, dp83902a Datasheet - Page 15

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

7 0 Packet Reception
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-
(Continued)
Received Packet Enters the Buffer Pages
Buffer Ring at Initialization
15
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
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
both Current Page Register and the Boundary Pointer Register
TL F 11157 – 10
TL F 11157 – 11