mx98743 Macronix International Co., mx98743 Datasheet - Page 12

• Manufacturer Part Number: mx98743
• Description: 100 Base Fast Ethernet Management Chip
• Manufacturer: Macronix International Co.

6.2 Receive Buffer Ring
Two pointers are used to control the Receive Buffer Ring. These are the Current Page Number Pointers
and the Select Page Number Pointer. The Current Number Pointer points to the first Page that MAC will
use to update the received data, whereas the Select Page Number Pointer points to the first page in the
Ring not yet read by the CPU. Under normal operation, the CPU activates Receive Enable Bit in the
Register 3C(MAC Control Register) and the packet beings arriving. The MAC starts storing the packet at
the location pointed to be the Current Page Number Pointer. If three packets have successfully arrived the
Buffer Ring and the CPU has not read a single page from the SRAM, the values of the Current and the
Select Page Number are equal. As a result, the Receive Enable bit is disable and it remains disabled
untile the CPU has removed at least one Packet data from the Ring to advance the Select Page Number
Pointer. Each time a packet is successfully written on the SRAM, an interrupt is issued. The CPU will
acknowledge interrupt and removes a packet from the Buffer Ring where the Select Page Number Pointer
is point to. Usually the Select Page Number Pointer will advance when a packet is removed. If the values
of Select Page Number and the Current Page Number are not equal, CPU will continue reading data from
the Buffer Ring. However, if the values are equal, CPU will abort reading activity. The following
procedures better illustrates how CPU handles different Receive Buffer Ring situations:
Initial Receive Enable procedure:
Procedure During Normal Receive Operation:
Procedure For Receive Buffer Overflow:
1. Get Current Page Number from the MAC Status Register.
2. Assign Select Page Number the value of Current Page Number and set Receive Enable bit.
1. If Select Page Number dose not equal to the Current Page Number, go to step 2.
2. Read Receive Buffer Ring data.
3. Assign Select Page Number to the next page.
4. Go back to step 1.
1. Read the Receive Buffer data.
2. Assign Select Page Number to the next page.
3. Read Receive Buffer data.
4. Assign Select Page Number to the next page.
5. Read Receive Buffer data.
6. Assign the Select Page Number to the next page.
7. Re-initial receive enable procedure.
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