dp83901a National Semiconductor Corporation, dp83901a Datasheet - Page 11

• Manufacturer Part Number: dp83901a
• Description: Serial Network Interface Controller
• 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-
ing a packet and is advanced when a packet is removed A
(Continued)
Received Packet Enters the Buffer Pages
Buffer Ring at Initialization
11
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 SNIC begins stor-
ing 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 corresponding to this
packet
both the Current Page Register and the Boundary Pointer Register
TL F 10469 – 8
TL F 10469 – 9