Altera 10-Gbps Ethernet MAC MegaCore Function - Manual (Page 155)

Appendix A: Frame Format A–3
Pause Frame
February 2014 Altera Corporation 10-Gbps Ethernet MAC MegaCore Function User Guide
A.3. Pause Frame
Figure A–4 shows the format of pause frames.
The length/type field has a fixed value of 0x8808, followed by a 2-byte opcode field of
0x0001. Subsequent two bytes define the pause quanta (P1 and P2); P1 is the most
significant byte. For XOFF pause frames, the MAC sets the pause quanta field to the
value of the tx_pauseframe_quanta register. For XON pause frames, the pause quanta
is 0. One pause quanta fraction is equivalent to 512 bit times, which equates to 512/64
(the width of the MAC data bus), or 8 cycles for the system clock.
The MAC sets the destination address field to the global multicast address, 01-80-C2-
00-00-01 (0x010000c28001) and the source address to the MAC primary address
configured in the tx_addrins_macaddr0 and tx_addrins_madaddr1 registers. Pause
frames have no payload length field, and is always padded with 42 bytes of 0x00.
Figure A–4. Pause Frame Format
Reserved[335:0] = 0x0
Frame Check Sequence[31:0]
Destination Address[47:0] = 0x010000c28001
Source Address[47:0] = MAC Primary Address
Pause Quanta[15:0] = 0xP1, 0xP2
(XOFF: P1,P2 = tx_pauseframe_quanta; XON: P1, P2 = 0x0)
6 Octets
6 Octets
2 Octets
42 Octets
4 Octets
Opcode[15:0] = 0x0001
Type[15:0] = 0x8808
2 Octets
2 Octets
SFD[7:0]
Preamble[47:0]
Start[7:0]
1 Octet
6 Octets
1 Octet