ax88796 ASIX Electronics Corporation, ax88796 Datasheet - Page 23

• Manufacturer Part Number: ax88796
• Description: Non-pci 8/16-bit 10/100m Fast Ethernet Controller With Embedded Phy
• Manufacturer: ASIX Electronics Corporation

INITIALIZATION OF THE BUFFER RING
Two static registers and two working registers control the operation of the Buffer Ring. These are the Page
Start Register, 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 removing 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.
BEGINNING OF RECEPTION
When the first packet begins arriving the AX88796 and begins storing the packet at the location pointed to by
the Current Page Register. An offset of 4 bytes is reserved in this first buffer to allow room for storing receive
status corresponding to this packet.
Page Start
Boundary Page
Current Page
Page Stop
AX88796 L
Physical Memory Map
Fig - 9 Receive Buffer Ring At Initialization
Buffer #1
Buffer #2
Buffer #3
Buffer #n
…
…
…
…
3-in-1 Local Bus Fast Ethernet Controller
4000h
8000h
23
n-2
n-1
Logic Receive Buffer Ring
ASIX ELECTRONICS CORPORATION
…
n
4
1
3
2